Modules

This combobox sets the dithering method. Floyd-Steinberg error diffusion – with some typical output bit depths – and random noise dithering are both supported. Floyd-Steinberg systematically distributes quantization errors over neighboring pixels, whereas random dithering just adds some level of randomness to break sharp tonal value bands. The default setting is “floyd-steinberg auto”, which automatically adapts to the desired output format.

This slider is only displayed if you choose method “random”. It controls the level of added random noise expressed as a damping factor in a 10*log ₂ basis. A value of -80 is a good fit for 8-bit output formats and -160 for 16-bit ones.

Sets the rendering intent for output/export. For more details see Section 3.2.6.3, “Rendering intent”).

Only rendering with LittleCMS2 gives you a choice of rendering intent. The option is hidden, if darktable's internal rendering routines are used. Rendering with LittleCMS2 is activated in the preferences dialog (see Section 8.6, “Processing”).

Sets the color profile for output/export, causing darktable to render colors with this profile. darktable embeds the profile data into the output file if supported by the file format – this allows other applications reading the file to correctly interpret its colors.

As not all applications, e.g. image viewers, are aware of color profiles, a general recommendation is to stick to sRGB as the default output profile. You should only deviate from sRGB if this is really required and if you know what you are doing.

The color reconstruction module replaces the color of all target pixels characterized by luminance values above this threshold. Inversely, only pixels with luminance values below this threshold are taken as valid source pixels for replacement colors. Too high settings of this parameter will cause the module to have no effect on any pixels. Too low values will minimize the “pool” of replacement colors – if no suited ones are available the original colors are maintained. Therefore, this parameter exhibits a “sweet spot” characteristic with an optimum setting depending on the individual image.

Defines the spatial distance (x,y-coordinates) that source pixels may have from a target pixel in order for them to contribute to color replacement. Higher values cause ever more distant pixels to contribute; this increases the chance to find a replacement color but makes that color more undefined and less clear.

Defines the range distance (difference in luminance values) that source pixels may have from target pixels in order for them to contribute to color replacement. Higher values cause more pixels to contribute even if their luminance differs more strongly from the target pixels; this again increases the chance to find a replacement color but at the same time increases the risk of unfitting colors creeping in.

This combobox defines if certain replacement colors shall take precedence over others. In its default setting “off ” all pixels contribute equally. Setting it to “saturated colors” makes pixels contribute according to their chromaticity – the higher saturated a color the more it contributes. By selecting “hue” you get a choice of giving precedence to a specific hue.

This slider is visible if you set the preference combobox to “hue”. It allows you to select a preferred hue of replacement colors. This only has an effect if the preferred hue is actually present within the selected spatial and range distance of the target pixels (see above). A typical use case is repairing highlights on human skin in situations where diverging colors are in close proximity (e.g. textiles or hair with a luminance close to skin). Setting a hue preference on skin tones avoids these other colors from creeping in.

The middle-grey luminance is the luminance in RGB space of the scene referred 18% grey. Its color picker tool reads the average luminance over the drawn area. If you happen to have a grey card or a color chart (IT8 chart or colorchecker) shot in the scene lighting conditions, then the grey color picker tool can be used to quickly sample the luminance of the grey patch on the picture. In other situations, the color picker can be used to sample the average luminance of the subject.

This setting has an effect on the picture that is analogous to a lightness correction. Values close to 100% do not compress the highlights but fail to recover shadows. Values close to 0% recover greatly the shadows but compress the highlights more harshly and result in local-contrast losses. The standard middle-grey value for linearly encoded camera RGB is 18%. Good values of grey are usually the average luminance of the whole picture or of the subject. In studio and indoors (low dynamic range scenes), proper grey values are found between 15-18%. In high dynamic range scenes (landscapes, back-lit portraits), proper grey values lie between 1.25 and 9%.

When modifying the middle-grey luminance, the white and black exposures are automatically slid accordingly, to preserve the dynamic range from clipping and to help you set the right parameter faster. If you are not happy with the auto adjustment performed by the grey slider, you can correct again the white and black exposure parameters afterwards.

The white relative exposure is the number of stops (EV) between pure white and the middle grey. It is the right bound of the dynamic range. It should be adjusted to avoid highlight clipping. The white exposure color picker tool reads the maximum luminance in RGB space over the drawn area, assumes it is pure white, and sets the white exposure parameter to remap the reading to 100% luminance.

When the grey is set at 18%, the white exposure will always be around 2.45EV. When the grey is set at 100%, the white exposure should be set at 0EV.

The black relative exposure is the number of stops (EV) between pure black and the middle grey. It is the left bound of the dynamic range. The black exposure color-picker tool reads the minimum luminance in RGB space over the drawn area, assumes it is pure black, and sets the black exposure parameter to remap the minimum reading to 0% luminance. The black color picker measurement is very sensitive to noise, and cannot identify if the minimum luminance is pure black (actual data) or just noise. It works better on low ISO pictures and with high quality demosaicing. When the color picker puts the black exposure at -16EV, it is a sign that the measure failed and you need to adjust it manually.

The black relative exposure allows you to choose how far you want to recover lowlights. Contrarily to the white exposure, it is not always possible to completely avoid clipping blacks. Every camera sensor has a maximum physical dynamic range for each ISO value (you can find them measured on DXOmark or DPreview), the software dynamic range in filmic rgb (dynamic range = white exposure - black exposure) should generally not be greater than the physical dynamic range of the sensor (10-14EV in most cases). Note that the dynamic range of the scene can be lower than the camera's one, especially indoors.

The auto-tune color picker combines all three color pickers above, and allows to set the grey, white and black exposures all at once, using the average of the drawn region as the grey estimation, the maximum as the white, and the minimum as the black. This gives good results in landscape photography but usually fails for portraits and indoor scenes.

When no true white and no true black are available on the scene, the maximum and minimum RGB values read on the image are not valid assumptions anymore, so the dynamic range scaling symmetrically shrinks or enlarges the detected dynamic range and the current parameters. This works with all color pickers, and adjusts the current values of white and black relative exposures.

The filmic rgb S-curve is created from the user parameters, by computing the position of virtual nodes and interpolating them, similarly to the tone curve module (but here, the nodes cannot be moved manually). The filmic rgb S-curve is split into three parts: a middle linear part, and two extremities that transition smoothly from the slope of the middle part to the ends of the exposure range.

The contrast slider controls the slope of the middle part of the curve, as illustrated in the graph display.

The contrast parameter drives the slope of the central part of the curve. The larger the dynamic range is, the greater the contrast should be set. This parameter mostly affects mid-tones.

When the contrast is set to 1, this disables the S-curve.

The latitude is the range between the 2 nodes enclosing the central linear portion of the curve, expressed as a percentage of the dynamic range defined in the scene tab (white-relative exposure minus black-relative-exposure). It is the luminance range that is remapped in priority, and it is remapped to the luminance interval defined by the Contrast parameter. It is usually advised to keep the latitude as large as possible, while avoiding clipping. If clipping is observed, you can compensate the effects by either decreasing the latitude, shifting the latitude interval with the shadow/highlights balance parameter, or by decreasing the contrast.

The latitude also defines the range of luminances that is not desaturated at the extremities of the luminance range (see the section called “Extreme luminance saturation (Look tab)”).

By default, the latitude is centered in the middle of the dynamic range. If this produces clipping in one part of the other of the curve, the balance parameter allows to slide the latitude along the slopes, towards the shadows or towards the highlights. This allows more room to be given to one extremity of the dynamic range than to the other, if the image properties demand it.

The darker curve in the graph of the module shows the desaturation of the extremities of the luminance range (black and white): since black and white do not have a color, they should normally be associated to 0% saturation. The default saturation is set to 100% in the range defined by the latitude, and decreases down to 0% outside of that range. One of the advantages of this operations is that, since color components do not clip at the same rate in the image, desaturating them avoids fringes around the high exposures.

If the bright colors feel too desaturated, you should check that the white-relative exposure setting does not clip the high luminance spots, and if not, increase the extreme luminance saturation parameter.

The preserve chrominance setting indicates how the chrominance should be handled by filmic rgb: either not at all, or using one of the provided three norms.

When applying the S-curve transformation independently on each color, the proportions of the colors get modified, which modifies the properties of the underlying spectrum, and ultimately the chrominance of the image. This is what happens if you choose no in the preserve chrominance parameter. This value may yield seemingly “better” results than the other values, but it may negatively impact later parts of the pipeline, when it comes to global saturation for example.

The other values of this parameter all work in a similar way. Instead of applying the S-curve to the channels R, G and B independently, filmic rgb uses a norm N, divides all the three components by that norm, and applies the S-curve to N. This way, the relationship between the channels is preserved.

The different values of the preserve chrominance parameter indicate which norm is used (the value used for N):

There is no "right" choice for the norm, depending on the picture to which it applies - you should experiment and decide for yourself on case by case basis.

The destination parameters set the target luminance values used to remap the tones through filmic rgb. The default parameters will work 99% of the times, the remaining 1% being when you output in linear RGB space (REC709, REC2020) for media handling log-encoded data. These settings are then to be used with caution because darktable does not allow separate pipelines for display preview and for file output.

The target black luminance parameter allows to set the ground-level black of the target medium. Set it greater than 0% if you want raised, faded blacks to achieve a retro look.

This is the middle-grey of the output medium, that is used as a target for the filmic rgb S curve central node. On gamma corrected media, the actual grey is computed with the gamma correction (middle-grey^(1/gamma)), so a middle-grey parameter of 18% with a gamma of 2.2 gives an actual middle-grey target of 45.87%.

The target white luminance parameter allows to set the ceiling level white of the target medium. Set it lower than 100% if you want dampened, muted whites to achieve a retro look.

The power of the output transfer function, often improperly called the gamma (only screen have a gamma), is the parameter used to raise or compress the mid-tones to account for the display non-linearities or to avoid quantization artifacts when encoding in 8 bits file formats. This is a common operation when applying ICC color profiles (except for linear RGB spaces, like REC 709 or REC 2020, which have a linear “gamma” of 1.0). However, at the output of filmic rgb, the signal is logarithmically encoded, which is not something ICC color profiles know to handle. As a consequence, if we let them apply a gamma 1/2.2 on top, it will result in a double up, and the middle-grey will be remapped to 76% instead of 45% as it should.

To avoid double ups and washed pictures, filmic rgb applies a “gamma” compression reverting the output ICC gamma correction, so the middle-grey is correctly remapped at the end. To remove this compression, set the destination power factor to 1.0 and the middle-grey destination to 45%.

This combobox toggles between “linear” and “logarithmic” view. In the logarithmic view more space is given to the lower values allowing a more fine-grained adjustment of the shadows.

This control triggers the exposure fusion feature. You can choose to merge the image with one or two copies of itself after applying the current base curve and boosting its exposure by a selectable number of ev units. The resulting image is thus a combination of two or three different exposures of the original image. Use this to compress dynamic range for extremely underexposed images or for true HDR input. For best results, use the exposure module (see Section 3.4.1.12, “Exposure”) to apply a suitable adjustment for correctly exposed highlights.

This slider is only visible if the exposure fusion feature is activated. It allows you to set the exposure difference between the merged images in ev units (default 1).

This slider is only visible if the exposure fusion feature is activated. It allows you to chose how the multiple exposures are computed. With a bias of 1 (the default), the image is fused with overexposed copies of itself. With a bias of -1, it is fused with underexposed copies. A bias of 0 tries to preserve the overall lightness of the image by combining both over and under-exposed copies of the image.

File selection is inactive as long as the 3D LUT folder (where you have stored your LUT files) is not defined in 3D LUT root folder under preferences/core options/miscellaneous.

A 3D LUT is relative to a specific color space. You have to select the one for which it has been built. Cube files are usually related to REC.709 while most of others are related to sRGB.

The interpolation method defines how to calculate output colors when input colors are not exactly on a node of the RGB cube (described by the 3D LUT). There are three interpolation methods available: tetrahedral (the default one), trilinear and pyramid. Usually you won't see any difference between the interpolation methods except with small size LUTs.

Set the operation mode for detecting fringes. “global average” is usually the fastest but might show slightly incorrect previews in high magnification. It might also protect the wrong regions of color too much or too little by comparison with local averaging. “local average” is slower because it computes local color references for every pixel, which might protect color better than global average and allows for rebuilding color where actually required. The “static” method does not use a color reference but directly uses the threshold as given by the user.

Set the spatial extent of the gaussian blur used for an edge detection. The algorithm uses the difference of gaussian-blurred and original image as an indicator for edges (a special case of the “difference of gaussians” edge detection). Try increasing this value if you either want a stronger detection of the fringes or the thickness of the fringe edges is too high.

Sets the threshold over which the edge of a pixel is counted as a “fringe”. The colors of the affected pixels will be rebuild from neighboring pixels. Try lowering this value if there is not enough fringe detected and try increasing this value if too many pixels are desaturated. You may additionally want to play around with the edge detection radius.

When you select the module in darkroom mode, it should look something like the image above (configurations with more than 24 patches are shown in a 7x7 grid instead). By default, it will load the 24 patches of a color checker classic and initialise the mapping to identity (no change to the image).

The grid shows a list of colored patches. The colors of the patches are the source points. The target color of the selected patch is shown as offsets controlled by sliders in the GUI under the grid of patches. An outline is drawn around patches that have been altered, i.e. the source and target colors differ.

The selected patch is marked with a white square, and its number is displayed in the combo box below. Select a patch by left clicking on it, or using the combo box, or using the color picker.

To modify the color mapping, you can change source as well as target colors.

The main use case is to change the target colors. You start with an appropriate palette of source colors (either from the presets menu or from a style you download). You can then change lightness (L), green-red (a), blue-yellow (b), or saturation (C) of the patches' target values via sliders.

To change the source color of a patch you select a new color from your image by using the color picker, and Shift+click on the patch you want to replace. You can switch between point and area sampling mode from within the global color picker panel (see Section 3.3.6, “Global color picker”).

To reset a patch, double-click it. Right-click a patch to delete it. Shift+click on empty space to add a new patch (with the currently picked color as source color).

The radius of the patch for similarity evaluation.

The strength of the denoise. Higher values lead to a stronger effect.

Amount of denoise to apply to luma. Select carefully in order not to lose too much structure.

Amount of denoise to apply to chroma. You can be much more aggressive with this parameter compared to luma.

The “Colour of the film base” section allows you to sample an area from your scan which comprises the base film stock. This is the area just outside of the image (IE. an unexposed part of the film). When working with black and white negatives, you can leave this at its default value of white. If working on color film, click the eye dropper to the right of the color bar. This will create a bounding box which covers about 98% of your image. Then, left-click and drag across an area of your negative which only has unexposed film stock in it. This will automatically calculate values for the “D min red component”, “D min green component” and “D min blue component” sliders. At this point, it is likely that your image will still look too dark.

Next we move to the D Max slider in the “Dynamic range of the film” section. This slider effectively sets our white point. Dragging this to the left will make the neg brighter. Dragging to the right will make the neg darker. If adjusting manually, it's a good idea to watch your histogram and ensure that you don't push the highlights into clipping (where the histogram is pushed off the right hand side of the graph). Again, you can use the eye dropper (on the right) to allow Negadoctor to automatically calculate this value to ensure maximal use of the histogram without clipping. If using the eye dropper, left-click and drag to draw a rectangle across only the exposed parts of the neg. Don't include the unexposed film stock in the rectangle, as this will skew the result.

Then, the “Scan exposure bias” slider under “Scanner exposure settings” allows us to set a black point. Dragging this to the left will make the neg brighter. Dragging to the right will make the neg darker. If adjusting manually, it's a good idea to watch your histogram and ensure that you don't push the shadows into clipping (where the histogram is pushed off the left hand side of the graph). Again, you can use the eye dropper to allow Negadoctor to automatically calculate any needed offset.

By now, your neg should be looking pretty close to what you were expecting to see. However, for color negs, you might need an extra step.

Moving to the “Corrections” tab, we have sliders which allow for corrections within both the shadows regions, and the highlight regions. Again, there are eye droppers to allow for automatic definition of shadow color casts, and/or highlight color casts. For shadows, select the eye dropper, and left-click and drag a large rectangle across the majority of your image. Negadoctor will calculate appropriate values, and these will be displayed under “shadows red offset”, “shadows green offset”,and “shadows blue offset”.

This settings should not be needed for most well-preserved negatives and will mostly be useful for old and poorly-preserved negatives having a decayed film base that induces undesirable color casts. Be aware that the shadows color cast setting will have no effect if the “scan exposure bias” setting, in the “film” tab, is set to a non-zero value.

It's important to understand that the Highlights white balance should always be calculated after shadows color cast, as the values of the shadows color cast sliders play a role in the values chosen for Highlights white balance (if using the eye dropper to have Negadoctor calculate those values). For highlight color casts, select the eye dropper and click and drag a rectangle across the brightest area of your image.

This setting should not be needed if your film has been exposed with a light source close to the one for which it was balanced, for example if you shot a scene lit by daylight on a daylight-balanced film.

On the “Print Properties” tab, we have sliders for “paper black”, “paper grade”, “paper gloss”, and “print exposure” adjustment.

These settings will mimic the tonal effect of photochemical papers that will finally create the real image, in the analog process.

For the “paper black”, select the eye dropper, and click and drag across only the exposed part of the negative. If you can see unexposed film stock around the edges of your image, ensure that these areas are excluded from the drawn rectangle for calculating the Paper black value.

Paper black represents the density of the blackest silver-halide cristal available on the virtual paper. Since that black density always results in non-zero luminance in the analog process, but the digital pipeline usually expects black encoded at zero (RGB value), this setting lets you remap paper black to pipeline black with an offset.

“Paper grade” is your gamma (contrast) control, and defaults to a value of 4. If all has gone well, this value (4) minus the value of D max (from the “Film Properties” tab) should leave you with a value between 2 and 3.

“Paper gloss” is essentially a highlights compression tool. As you drag this slider to the left, you will see in the histogram that the highlight values are being compressed (pushed to the left). Adjust this accordingly, so that your highlights are not clipped in the histogram or to simulate a mat printing with low-contrast highlights.

The “Print exposure adjustment” slider is to correct any last minute clipping of highlights, although if you have followed all prior instructions, you shouldn't need it. It is also possible to increate print exposure while deccreasing the paper gloss to brighten midtones without losing highlights.

Choose the profile or color matrix to apply, darktable offers many widespread matrices along with an enhanced matrix for some camera models. The enhanced matrices were processed by the darktable team in order to provide a look closer to the manufacturer's.

You can also supply your own input ICC profiles and put them into $DARKTABLE/share/darktable/color/in or $HOME/.config/darktable/color/in. $DARKTABLE is used here to represent darktable's installation directory and $HOME your home directory. One common source of ICC profiles is the software that is shipped with your camera; it often contains profiles specific to your camera model. You may need to activate module unbreak input profile (see Section 3.4.1.17, “Unbreak input profile”) to use your extra profiles.

If your input image is a low dynamic range file like JPEG, or a raw in DNG format, it might already contain an embedded ICC profile which darktable will use as a default. You can always overrule darktable and select a different profile. Select “embedded icc profile” to restore the default.

This combobox lets you activate a color clipping mechanism. In most cases you can leave it at its default “off” state. However, if your image shows some specific features like highly saturated blue light sources, gamut clipping might be useful to avoid black pixel artifacts. See Section 3.2.6.6, “Possible color artifacts” for more background information.

You can select from a list of RGB profiles. Input colors with a saturation that exceeds the permissible range of the selected profile get clipped to a maximum value. “linear Rec2020 RGB” and “Adobe RGB (compatible)” allow for a broader range of unclipped colors, while “sRGB” and “linear Rec709 RGB” produce a tighter clipping. You should select the profile that prevents artifacts while still maintaining highest color dynamics.

Defines the mode of operation. Defaults to “manual”.

Automatically remove the camera exposure bias (only available in “manual” mode). The camera exposure bias is the EV compensation of the camera lightmeter, commonly used to prevent highlight clipping, for photographers who expose to the right of the histogram. This feature relies on reading the EXIF field

ExposureBiasValue

which must be correctly filled in the RAW file by the camera for it to work.

Note: for Fuji RAWs, it will be necessary to add aditional +0.75 EV, for an overall correction of +1.25 EV, to compensate for their native underexposure.

Adjust the exposure correction [EV] (only available in “manual” mode).

darktable can calculate correct black level and exposure values for your image based on the content of a rectangular area. The adjustment slider lets you define what percentage of bright values are to be clipped out in the calculation. Pressing the icon starts the calculation and lets you draw a rectangular area of your choice using your mouse. This feature is only available in “manual” mode.

Adjust the black level in both “manual” and “automatic” mode.

Defines a location in the histogram for automatic exposure correction. A percentile of 50% denotes a position in the histogram where 50% of pixel values are below and 50% of pixel values are above. For more details see percentile . Only available in “automatic” mode.

Defines the target level for automatic exposure correction in terms of [EV] relative to the white point of the camera. The white point is camera specific and defines the highest lightness value that the camera sensor can detect. Only available in “automatic” mode.

This tool is used to flip the image on the horizontal,vertical or both axis.

This tool corrects the rotation angle helping you level an image. You can either set a numerical value or use your mouse directly on the image. To use your mouse, right-click, hold it down and draw a line along a suited horizontal or vertical feature; as soon as you release the mouse button the image is rotated so the line you drew matches the horizontal/vertical axis.

This tool is used to correct perspective distortions in your image. Useful for example when you shoot a high building from ground with a short focal length, aiming upwards with your camera. The combobox lets you select the type of correction you want to use :

Depending on the selected correction type you will see two or four straight adjustment lines overlaid to your image. Two red circles on every line let you modify the line positions with your mouse. Each line additionally carries a “symmetry” button. If activated (and highlighted in red) all movements of the affected line will be mirrored by the opposite line. In order to correct perspective distortions, you need to find suitable horizontal and/or vertical features in your image and align the adjustment lines with them. When done, press the “OK” button, which is located close to the center of your image. The image will be corrected immediately. You can at any time come back and refine your corrections by selecting “correction applied” in combobox keystone.

Use this options to avoid black edges on the image borders. Useful when you rotate the image.

Here you can change what aspect ratio you want to have on the result, thus constraining the proportion of width and height of the crop rectangle to the aspect ratio of your choice. Many common numerical ratios are pre-defined. A few special aspect ratios deserve explanation:

You can also select any other ratio after opening the combobox and typing it in the form of “x:y”. If you want a certain aspect ratio to be added to the pre-defined ones you can do so by including a line of the form

plugins/darkroom/clipping/extra_aspect_ratios/foo=x:y
	

into darktable's configuration file $HOME/.config/darktable/darktablerc. Here “foo” defines the name of the new aspect ratio and “x” and “y” the corresponding numerical values.

Many self-explaining guides are available to help you compose your image.

In case the chosen guidelines are not symmetrical relative to the image frame, you can flip them on the horizontal,vertical or both axis.

In the margins tab, you can directly set the distance between the border of the uncropped image and the crop rectangle for the four margins. The values are specified in percent of the width/height of the uncropped image. These values will be updated if you move or resize the crop rectangle with the mouse.

Clicking on one of the buttons causes a counter-clockwise or clockwise rotation in steps of 90 degrees.

This parameter controls a rotation of the image around its center and can correct for a skewed horizon.

This parameter corrects converging lines horizontally.

This parameter corrects converging lines vertically. In some cases you get a more naturally looking image if you correct vertical distortions not to their full extent but rather at an 80 to 90% level. If desired just reduce the value after having performed the automatic correction.

This parameter shears the image along one of its diagonals and is needed when correcting vertical and horizontal perspective distortions simultaneously.

If activated a number of guide lines is laid over the image to help you judge the quality of the correction.

When activated the automatic cropping feature clips the image to get rid of any black corners. At your choice you can either clip to the “largest area” or to the largest rectangle maintaining the original aspect ratio (“original format”). In the latter case you can manually adjust the automatic cropping result: left click into to clip region and move it around. The size of the region gets modified automatically excluding any black corners.

This parameter controls how lens and camera specifics are taken into account. If set to “generic” a focal length of 28mm on a full-format camera is assumed. If set to “specific”, focal length and crop factor can be set manually.

The focal length of the lens used. The default value is taken from the Exif data of your image. This parameter is only effective and visible if the “specific” lens model has been selected.

The crop factor of the camera used. You will typically need to set this value manually. This parameter is only effective and visible if the “specific” lens model has been selected.

If the “specific” lens model has been selected this parameter allows for a free manual adjustment of the image's aspect ratio.

Clicking on one of the icons starts an automatic fitting of the module parameters based on the selected vertical and/or horizontal lines. You can choose to correct only vertical distortions ( ), only horizontal distortions ( ), or both types of distortions simultaneously ( ). Ctrl+clicking on either icon only fits rotation. Shift+clicking on either icon only fits vertical and/or horizontal lens shift.

Clicking on the icon causes the image to be (re-)analyzed for suitable line segments. Shift+clicking applies a prior contrast enhancement step, Ctrl+clicking applies an edge enhancement step. Both variations can be used alone or in combination if the default is not able to detect a sufficient number of lines. Clicking on the icon discards all collected structural data. By clicking on the icon you can switch the overlay display of line segments on and off.

The strength parameter controls the amount of haze removal. Setting it to unity, the module removes 100 percent of the detected haze between the camera and up to the specified distance; see below. Negative values for the strength increase the amount of haze in the image.

This parameter limits the distance up to which haze is removed. For small values, haze removal is restricted to the foreground of the image. Haze is removed from the foreground to the far background if the distance parameter is set to unity. In case of a negative strength the distance control has no effect.

Set the upper limit for the region counted as shadows and where no gamma correction is performed. Typically values between 0.0 and 0.1 are required by the profile.

Set the gamma value to compensate your input profile. Often the required value is 0.45 (the reciprocal of 2.2 gamma used by some manufacturer's profile).

The camera make and model as determined by Exif data. You can override this manually and select your camera from a hierarchical menu.

Only lenses with correction profiles matching the selected camera will be shown.

The lens make and model as determined by Exif data. You can override this manually and select your lens from a hierarchical menu. This is mainly needed for pure mechanical lenses, but may also be needed for off-brand / third party lenses.

Corrections additionally depend on certain photometric parameters that are read from Exif data: focal length (needed for distortion, TCA, vignetting), aperture (needed for TCA, vignetting) and focal distance (needed for vignetting). Many cameras do not record focal distance in their Exif data; most likely you need to set this manually.

You can manually override all automatically selected parameters. Either take one of the predefined values from the pull-down menu; or – with the pull-down menu still open – just type in your own value.

If your system's lensfun library has no correction profile for the automatically identified camera/lens combination the controls for the three photometric parameters are not displayed, and you get a warning message instead. You may try to find the right profile yourself by searching for it in the menu. If you can't find your lens, check if it is in the list of currently supported lenses, and refer to the lensfun-update-data tool. If there is no matching profile for your lens, please visit this lens calibration service offered by Torsten Bronger, one of darktable's users. Alternatively you may go to lensfun's home page and learn how to generate your own set of correction parameters. Don't forget to share your profile with the lensfun team!

This combobox gives you a choice about which corrections (out of distortion, TCA and vignetting) darktable shall apply. Change this from its default “all”, if your camera has already done some internal corrections (e.g. of vignetting), or if you plan to do certain corrections with a separate program.

In addition to the correction of lens flaws, this module can change the projection type of your image. Set this combobox to the aimed projection type, like “rectilinear”, “fish-eye”, “panoramic”, “equirectangular”, “orthographic”, “stereographic”, “equisolid angle”, “thoby fish-eye”.

This slider allows you to adjust the scaling factor of your image. Pressing the auto scale button (right to the slider) will let darktable find the best fit to avoid black corners.

The default behavior of this module is to correct lens flaws. Switch this combobox to “distort” in order to simulate the behavior of a specific lens (inverted effect).

This slider allows to override the correction parameter for TCA. You can also use this slider to manually set the parameter in case the lens profile does not contain TCA correction. Look out for colored seams at features with high contrast edges and adjust this parameter and the following one to minimize those seams.

This slider allows to override the correction parameter for TCA. You can also use this slider to manually set the parameter in case the lens profile does not contain TCA correction.

You will sometimes observe that for a given camera/lens combination only part of the possible corrections (distortion, TCA, vignetting) are supported by lensfun's profiles. This message box will tell you what corrections have actually been applied.

Set the spatial extent of the gaussian blur.

Blur intensity for red channel.

Blur intensity for green channel.

Blur intensity for blue channel.

Based on Exif data of your raw file, darktable will automatically determine the camera model and ISO setting. If found in its database, the corresponding noise profile will be used. If your image has an intermediate ISO value, the statistical properties will be interpolated between the two closest datasets in the database, and this interpolated setting will show up as the first line in the combo box. You also have the option to manually overwrite this selection to suit your personal preferences better. The top-most entry in the combo box brings you back to the profile darktable deems most suited.

This module can eliminate noise by two different core algorithms. Both “non-local means” and “wavelet” can tackle efficiently luma (lightness) noise and chroma (color) noise. “wavelet” mode also lets you adjust the force of the denoising depending on the noise coarseness. If needed you can apply two instances of this module (see Section 3.2.4, “Multiple instances”): one instance to tackle luma noise with blend mode “lightness” or “HSV lightness”, and another one to tackle chroma noise with blend mode “color” or “HSV color ”. An example of the use of two instances with blending modes is available within the presets of this module. For more information on blend modes have a look at Section 3.2.5.4, “Blending operators”. The module also offers an automatic mode for each algorithm. Automatic modes allow to set module's parameters in an easier way, as it guesses several parameters from the profile. All sliders of this module can take values higher than their bounds if needed using Right-click.

As white-balance amplifies the RGB channels differently, they exhibit different noise levels. This checkbox makes the algorithm adaptive to white balance. This option should be disabled on the second instance if you use a first instance with a color blend mode.

This slider is only available if mode “non-local means” is selected. It controls the size of the patches being matched when deciding which pixels to average (see also Section 3.4.1.9, “Denoise – non local means”). Set this to higher values as the noise gets higher. Beware that high values may smooth out small edges though. Processing time will stay about the same.

This slider is only available if mode “non-local means” is selected. It controls how far from a pixel the algorithm will try to find similar patches. Increasing the value can give better results for very noisy images when coarse grain noise is visible, but you should better use the scattering slider instead. The processing time is hugely impacted by this parameter: it depends on the square of the parameter. A lower value will make execution faster, a higher value will make it slower.

This slider is only available if mode “non-local means” is selected. Like the search radius, it controls how far from a pixel the algorithm will try to find similar patches, but does this without increasing the number of patches considered. As such, processing time will stay about the same. Increasing the value will reduce coarse grain noise, but may smooth local contrast. This slider is particularly effective to reduce chroma noise.

This slider is only available if mode “non-local means” or “non-local means auto” is selected. It controls the amount of details which should be preserved by the algorithm. It can be used as a way to control the amount of luma noise smoothing: giving a big value to this slider will result mostly in chroma noise smoothing with little smoothing of luma noise. This slider has no effect if patch-size is set to 0.

These curves are only available if mode “wavelet” is selected. The noise of an image is usually not only fine grain, but also more or less coarse grain. These curves allow to denoise more or less depending on the coarseness of the visible noise. The left of the curve will act on very coarse grain noise, while the right of the curve will act on very fine grain noise. Pushing up the curve will result in more smoothing, pulling it down will result in less smoothing. As an example, you can preserve very-fine grain noise by pulling down the rightest point of the curve until the minimum value. As another example, if you are tackling chroma noise with a blend mode, you can push up the right part of the curve, as colors are not supposed to change a lot on fine grain scales: this will help especially if you see some isolated pixel left undenoised.

Considering R, G, and B curves, the best way to use them is to look at one of the channel using the channel mixer module in gray mode, denoise this particular channel, and then do the same for the other channels. This way, you can take into account the fact that some channel may be noisier than others into your denoising. Be aware that guessing which channel is noisy without actually seeing the channels individually is not straightforward and can be counterintuitive: a pixel which is completely red may not be caused by noise on the R channel, but actually by noise on B and G channels.

This parameter is here to fine-tune the strength of the denoise effect. The default value has been chosen to maximize the peak signal to noise ratio. It's mostly a matter of taste if you prefer a rather low noise level at the costs of a higher loss of detail, or if you accept more remaining noise in order to have finer structures better preserved within your image.

This option is available in “wavelets” and “non local means” modes. It allows to denoise more agressively the shadows or the highlights. Lower the value to denoise more the shadows than the highlights. Usually, as noise increases, you will need to lower this value.

This option is available in “wavelets” and “non local means” modes. It allows to correct the color cast that may appear in the shadows. Increase this value if dark shadows appear too greenish, decrease it if they appear purple-ish.

This option is available in “auto” modes. In these modes, darktable tries to derive denoising parameters from the camera profile. Depending on your image the automatically derived parameters may not be optimal. E.g. if your image is heavily underexposed and you lifted the exposure, you will have to increase this parameter to get a proper denoising. This parameter should reflect the amplification you add to your image: if you add 1EV of exposure, the signal is multiplied by 2, so this parameter should be set to 2.

Set the demosaic method. darktable currently supports PPG, AMAZE, and VNG4 for Bayer sensors. For X-Trans sensors darktable supports VNG, Markesteijn 1-pass, and Markesteijn 3-pass.

Set the threshold for an additional median pass. Defaults to “0” which disables median filtering. This option is not shown for X-Trans sensors.

Activates a number of additional color smoothing passes. Defaults to “off”.

In some cameras the green filters have slightly varying properties. This parameter adds an additional equalization step to suppress artifacts. Available options are “disabled”, “local average”, “full average” and “full and local average”. This option is not shown for X-Trans sensors.

Set the threshold for noise detection. Higher values lead to stronger noise removal and higher loss of image detail.

The noise of an image is usually not only fine grain, but also more or less coarse grain. These curves allow to denoise more or less depending on the coarseness of the visible noise. The left of the curve will act on very coarse grain noise, while the right of the curve will act on very fine grain noise. Pushing up the curve will result in more smoothing, pulling it down will result in less smoothing. As an example, you can preserve very-fine grain noise by pulling down the rightest point of the curve until the minimum value. As another example, if you are tackling chroma noise with a blend mode, you can push up the right part of the curve, as colors are not supposed to change a lot on fine grain scales: this will help especially if you see some isolated pixel left undenoised. Considering R, G, and B curves, the best way to use them is to look at one of the channel using the channel mixer module in gray mode, denoise this particular channel, and then do the same for the other channels. This way, you can take into account the fact that some channel may be noisier than others into your denoising. Be aware that guessing which channel is noisy without actually seeing the channels individually is not straightforward and can be counterintuitive: a pixel which is completely red may not be caused by noise on the R channel, but actually by noise on B and G channels.

The threshold of the detection, i.e. how strong a pixel's value needs to deviate from its neighbors to be regarded as a hotpixel.

The strength of blending hotpixels with their surrounding.

This will extend the detection of hotpixels, it will even regard a pixel as hot if a minimum of only three (instead of four) neighbor pixels deviate by more than the threshold level.

This options will mark the pixels that have been corrected. It also displays the count of detected and fixed pixels.

Choose the method for highlight reconstruction.

Manually adjust the clipping threshold against magenta highlights. The default is usually satisfactory without any need for additional adjustments.

The only control element of this module is a color selector which allows to adjust for different colors of your film material. Clicking on the colored field will open a color selector dialog which offers you a choice of commonly used colors, or allows to define a color in RGB color space. You can also activate a color picker by pressing and take a color probe from your image – preferably from the unexposed border of your negative.

The camera specific black level of the four pixels in the RGGB Bayer pattern. Pixels with values lower than that level are considered to contain no valid data.

The camera specific white level. All pixels with values above are likely to be clipped and handled accordingly in the highlight reconstruction module (see Section 3.4.1.27, “Highlight reconstruction”). Pixels with values equal to the white level are considered to be white.