editing an image: display-referred workflow
This is a legacy mode which is retained to provide backward-compatibility with edits in older darktable versions, and to allows users to continue with their former way of working without forcing them to use the newer scene-referred workflow.
The display-referred workflow places more emphasis on performing image processing in the non-linear display-referred part of the pixelpipe. By default it uses the base curve module to tone map images from the linear scene-referred space into display-referred space, although other tone-mapping tools (such as the tone curve module) can also be used. Many modules are moved later in the pipeline (after this tone mapping transition) so that they work with gamma-encoded (display-referred) pixel values rather than linearly-encoded (scene-referred) pixel values.
Most of the basic steps required to develop images under the display-referred workflow are quite similar to the scene-referred workflow. The main differences lie in the choice of modules, and the order in which they appear in the pixelpipe. To see the difference in the ordering of the modules between the display-referred and scene-referred workflows, please refer to the default module order section.
Note: This section discusses a number of legacy modules that are no longer recommended for use in the scene-referred workflow, and new users are recommended to instead refer to the scene-referred section for a guide to how best to process images in darktable.
- white balance
- The white balance module works the same as in scene-referred workflow and, by default, uses the white balance coefficients provided by the camera. If this does not give acceptable results, use the camera presets or take the white balance from a neutral spot in your image. The temperature slider can be used to make the image “warmer” or “cooler”. More advanced color grading is better left to other modules, as discussed later.
- exposure correction
- The exposure module works the same as in scene-referred mode, but the way you use it is a little different. In display-referred mode, you need to make sure you don’t blow out your highlights too much, and use the base curve module to adjust the middle tones if needed.
While you can use the exposure module to tweak the black level to supply more contrast, you need to be very careful doing this as you can end up with negative RGB values. It is better to increase the contrast by adjusting the toe of the base curve, however this can be a little fiddly and it is one of the reasons why the filmic rgb module was introduced to darktable.
- noise reduction
- As with the scene-referred workflow, the best starting point for noise reduction is the denoise (profiled) module. Similarly, you may also choose to use raw denoise, surface blur, astrophoto denoise, or the contrast equalizer module.
- fixing spots
- As with the scene-referred workflow, you can use the retouch, spot removal and hot pixels modules to correct artifacts in your image.
- geometrical corrections
- As with the scene-referred workflow you can use the crop and rotate, perspective correction and lens correction modules to correct distortions and crop your image.
- bringing back detail
- Raw images often contain more information than you can see at first sight, especially in the shadows. The shadows and highlights module helps bring these details back into visible tonal values. Structural details in fully blown-out highlights, by nature of the digital sensor, can not be recovered. However, you can correct unfavorable color casts in these areas with the highlight reconstruction module. The color reconstruction module is able to fill overexposed areas with suitable colors based on their surroundings. The filmic rgb module also offers highlight reconstruction, but be sure to disable base curve first.
- adjusting tonal values
- Almost every workflow is likely to include adjusting the image’s tonal range and darktable offers several modules to assist with this. The most basic is the contrast brightness saturation module. In the tone curve module, tonal values are adjusted by constructing a curve. The levels and rgb levels modules offer a concise interface, with three markers in a histogram. And of course, there is nothing to stopping you from using the filmic rgb module in a display-referred workflow if you so wish (after disabling base curve).
- enhancing local contrast
- Local contrast enhancement can emphasize detail and clarity in your image. Carefully used, it can give your photograph the right pop. Several modules are available for this task. The local contrast module is easy to handle, with just a few parameters. A much more versatile, but also more complex, technique is offered by the contrast equalizer module. Take a look at its presets to get a feeling for how it works. The contrast equalizer is darktable’s “Swiss Army Knife” for many adjustments where spatial dimension plays a role. Note that the location of this module in the pixel pipeline differs significantly between the scene-referred and display-referred workflows.
- color adjustments
- darktable offers many modules for adjusting colors in an image. A very straightforward technique is implemented in the color correction module. Use this module to give an image an overall tint or to adjust overall color saturation. The color zones module offers a much finer control to adjust saturation, lightness and hue, in user defined zones. The tone curve module – in addition to the classical adjustment of tonal values – gives you fine control over the colors in an image. Finally, if you intend to convert an image into black & white, a good starting point, with an easy to use and intuitive user interface, is offered by the monochrome module. Alternatively, you might consider using the color calibration module.
- If you start your workflow from a raw image, your final output will need to be sharpened. The sharpen module can do this with the classical USM (unsharp mask) approach, available in most image processing software. Another very versatile way to enhance edges in an image is offered by the highpass module, in combination with darktable’s rich set of blending operators.
- artistic effects
- darktable comes with a rich set of artistic effect modules. For example you can use the watermark module to add a watermark to your image. The grain module simulates the typical noise of classical analogue footage. Use the color mapping module to transfer the look and feel of one color image onto another. The low light module allows you to simulate human vision to make lowlight pictures look closer to reality. The graduated density filter adds a neutral or colored gradient to your image for exposure and color correction.