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width
: The width of the Gaussian curve. This number is expressed in zones, with the full range being 10 zones.
tone equalizer
Dodge and burn while preserving local contrast.
When used together with [_filmic rgb_](./filmic-rgb.md), this module replaces the need for other tone-mapping modules such as the [_base curve_](./base-curve.md), [_shadows and highlights_](./shadows-and-highlights.md), [_tone curve_](./tone-curve.md) and [_zone system (deprecated)_](./zone-system.md) modules. It works in linear RGB space and utilizes a user-defined mask to guide the dodging and burning adjustments, helping to preserve local contrast within the image.
The following diagram describes how the tone equalizer works:
![tone-equalizer-mask](./tone-equalizer/tone-equalizer-overview.png#w100)
Create a monochrome [_guided mask_](#masking-tab) that divides the input image into regions of similar luminosity. The resulting mask should blur the fine details within the image so that pixels within each region are all treated similarly, preserving local contrast.
Adjust the sliders in the [_simple_](#simple-tab) tab or the equalizer graph in the [_advanced_](#advanced-tab) tab to alter the brightness of the underlying image, based on the brightness of the mask. Exposure can also be adjusted by scrolling with the mouse while hovering the cursor over the preview image (see [_cursor indicator/control_](#cursor-indicatorcontrol) for details).
In the simple tab, each slider corresponds to a single brightness zone (EV) in the mask, which can be raised or lowered to adjust the exposure of the image where the mask's brightness lies in that zone. Similarly, in the equalizer tab, the horizontal axis of the graph corresponds to the brightness level of the mask, and the vertical axis specifies the required exposure adjustment to pixels where the mask matches that brightness level.
The exposure of each pixel of the input image is adjusted using the mask and the equalizer graph. For each pixel, the module looks up the brightness of the mask at that point, finds the matching brightness on the horizontal axis of the equalizer graph, and increases or decreases the exposure accordingly (using the vertical axis of the graph).
It is important that the mask separates the image into regions of similar brightness, and that a suitable amount of blur is applied within those regions. This means that all of the pixels in each region will have their exposure adjusted similarly, without adversely affecting local contrast. Examine your image beforehand to identify which regions you wish to dodge and burn, and use the controls on the [_masking_](#masking-tab) tab to ensure that those areas are reasonably separated in tone within the final mask. This will allow those regions to be adjusted independently.
The controls of the _tone equalizer_ module are divided between three tabs.
display exposure mask
: Click on the icon to the right of this label to show/hide the module's guided mask over the top of the image. This control is available in all three tabs.
simple tab
This tab splits the brightness of the guided mask into nine zones (from --8 to 0 EV) and allows you to alter each zone independently. This is a simplified interface and is used to generate the same tone adjustment curve as shown in the [_advanced_](#advanced-tab) tab.
--8 EV ... 0 EV
: Each slider adjusts the exposure of all pixels where the _guided mask_ has the given brightness. If the mask's histogram is evenly spread over the entire tonal range, sliders towards the top generally affect the shadows, whereas sliders towards the bottom generally affect the highlights. You can check the spread of the histogram within the [_advanced_](#advanced-tab) tab.
advanced tab
This tab allows you to control the same intensity levels as in the simple tab, though here they are represented as control points on a curve. Behind the curve is a histogram representing the intensity levels of the _guided mask_ (not the underlying image). If the histogram is too bunched up, this means your mask doesn't have a good spread of intensity levels, which makes it harder to independently control the brightness of the different parts of your image. It is therefore recommended that the histogram be adjusted so that it extends the entire range, covering as many control points as possible for maximum flexibility. You can adjust the mask using the controls in the [_masking_](#masking-tab) tab.
Click+drag the control points on the curve to adjust the brightness of all pixels where the mask has the given intensity. If the mask's histogram is evenly spread over the entire tonal range, control points to the left will generally affect the shadows, and control points to the right will generally affect the highlights. Moving a single control point will also affect control points on either side to ensure the curve remains smooth. This behaviour can be adjusted using the _curve smoothing_ control.
curve smoothing
: Control how the curve is interpolated between control points. Move the slider to the right to make the transitions between the control points more gradual, but beware that going past about 0.6 can introduce some instability (oscillations) in the curve due to mathematical constraints. Move the slider to the left for a more well-behaved curve, but beware that this can result in harsher tonal transitions that may damage local contrast.
masking tab
By default, only the lenses that are directly compatible with your camera's mount are listed and automatically identified. If you are using lenses for a different mount with an adapter (for example a Four Thirds lens adapted to a Micro Four Thirds body), then you must run the [`lensfun-add-adapter`](https://lensfun.github.io/manual/v0.3.2/lensfun-add-adapter.html) tool to enable those lenses.
This tab contains controls for adjusting the guided mask.
The purpose of the guided mask is to separate out areas with different tonal ranges so that they can be independently brightened or darkened by the tone equalizer. The masking filters are designed to allow sharp edges between these areas to be preserved, while blurring details within a given tonal range, so that the brightness can be adjusted without adversely impacting local contrast. Ideally the mask histogram shown in the _advanced_ tab should be spread out across all of the control points.
To avoid having to switch back and forth between the _advanced_ and _masking_ tabs, a gray bar under the "mask post processing" label displays a representation of the middle 80% of the histogram. By using the controls in this tab to center and spread out this gray bar, you can expect to have a nicely shaped histogram when you return to the "advanced" tab. If you see orange at either end of the gray bar, this means that part of the histogram is outside of the 9 EV range of the mask, and needs to be further adjusted.
correction method
: Choose which method to use to correct distortions. Some cameras are able to embed lens correction data into the metadata of their Raw files. Where supported metadata is found, you can choose to use either the embedded correction data (choose "embedded metadata") or that provided by the lensfun project (choose "lensfun"). Additional controls will be provided depending on the option selected.
corrections
: Choose which corrections (distortion, TCA, vignetting) darktable should apply. Change this from its default "all", if your camera has already performed some internal corrections (e.g. vignetting), or if you plan to undertake some corrections with a separate program.
![tone-equalizer-mask-histogram](./tone-equalizer/tone-equalizer-mask-histogram.png#w33)
When setting up the guided mask you will need to strike a balance between obtaining a smooth blur within tonal regions (to preserve local contrast) and preservation of the boundaries between those regions. Some experimentation will be required to find the best settings. Often the key controls to adjust are the _exposure/contrast compensation_ sliders at the bottom of the module.
Displaying the guided mask while making these adjustments will help you to understand these controls and better judge the quality of the mask.
luminance estimator
: Choose the method by which the luminance of a pixel will be estimated when mapping it to a mask intensity value (default _RGB euclidean norm_).
preserve details
: Choose the smoothing algorithm used to blur the mask:
- _no:_ Do not smooth the mask (the effect is the same as using normal tone curves). When the module is used to compress dynamic range, this option can cause compression of local contrast. This can be useful when increasing (local and global) contrast.
- _guided filter:_ Use the original guided filter algorithm to blur the mask while attempting to preserve edges. One of the limitations of this algorithm is that the guided filter is exposure-sensitive, meaning that shadows tend to be blurred more than highlights. Note that this limitation can sometimes be an asset: if one wants to lighten shadows a lot, the guided filter can provide very good local contrast preservation.
- _average guided filter:_ Use this option in cases where the effect of the guided filter is too strong. In this mode, a geometric mean is taken between the output of the original _guided filter_ algorithm and the output given by the _no_ option.
- _eigf (default):_ The _exposure-independent guided filter_ solves the problem of the original _guided filter_, in that it makes the degree of blurring independent of the exposure. This means the degree of blurring applied to the highlights and the shadows regions should be about the same. This improved algorithm is now the default option.
- _averaged eigf:_ This option takes the geometric mean between the _eigf_ mask and the mask generated by the _no_ option, and is useful in cases where the degree of blurring in the mask needs to be mitigated.
filter diffusion
: By default this is set to a value of 1, meaning that the filtering algorithm is run once on the input image to produce the blurred monochrome mask.
: If you increase this to 2, the filtering algorithm will be run once on the input image to produce an intermediate mask, and then a second time on the intermediate mask. As a result, the final mask will be more blurred than when using a single iteration. Progressively higher values will diffuse the mask even further. However, because the mask filtering algorithm is run multiple times, each iteration will increase the processing time.

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Source string description
type: Plain text
Flags
md-text, no-wrap, read-only
Source string location
content/module-reference/processing-modules/tone-equalizer.md
String age
2 years ago
Last updated
2 months ago
Source string age
2 years ago
Translation file
po/content.pot, string 1470