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16 changes: 8 additions & 8 deletions content/module-reference/processing-modules/filmic-rgb.md
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Expand Up @@ -212,19 +212,19 @@ hardness (previously _target power factor function_)
: This parameter is the power function applied to the output transfer function, and it is often improperly called the _gamma_ (which can mean too many things in imaging applications, so we should stop using that term). It is used to raise or compress the mid-tones to account for display non-linearities or to avoid quantization artifacts when encoding in 8 bit 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 of 1/2.2 on top, it will result in a double-up, which would cause the middle-gray to be remapped to 76% instead of 45% as it should in display-referred space.

latitude
: The latitude is the range between the two nodes enclosing the central linear portion of the curve, expressed as a percentage of the dynamic range defined in the [_scene_](#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 advisable to keep the latitude as large as possible, while avoiding clipping. If clipping is observed, you can compensate by either decreasing the latitude, shifting the latitude interval with the _shadow ↔ highlights balance_ parameter, or decreasing the contrast.
: The latitude is the range between the two nodes enclosing the central linear portion of the curve, expressed as a percentage of the dynamic range defined in the [_scene_](#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. While it is set to 0 by default, it is usually advisable to keep the latitude as large as possible, while avoiding clipping. If clipping is observed, you can compensate by either decreasing the latitude, shifting the latitude interval with the _shadow ↔ highlights balance_ parameter, or decreasing the contrast.
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I've not reviewed all of the text in the PR but this paragraph is the reason I haven't resolved that issue so far. The recommendation (keep the latitude large) comes from the original developer. But since he is also the person who changed the default value to 0, it's hard to justify keeping that recommendation. Unfortunately since he's stopped talking to anyone involved in darktable now, it's hard to resolve this contradiction or understand his reasoning for the change.

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Maybe the least worst option might be to just remove reference to the recommendation altogether

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I don't know if this is a contradiction. I believe it makes sense to set the latitude as wide a possible to control the roll-off at the edges, but the default is set at zero so the user can decide the settings to use. At least, that's how I see it. Personally, I don't bother with latitude, so I'm ok with the change or to remove that discussion altogether.


: The latitude also defines the range of luminances that are not desaturated at the extremities of the luminance range (See _mid-tones saturation_).

shadows ↔ highlights balance
: By default, the latitude is centered in the middle of the dynamic range. If this produces clipping at one end of the curve, the balance parameter allows you to slide the latitude along the slope, 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 properties of the image demand it.

mid-tones saturation / extreme luminance saturation / highlights saturation mix
: At extreme luminances, the pixels will tend towards either white or black. Because neither white nor black have color associated with them, the saturation of these pixels must be 0%. In order to gracefully transition towards this 0% saturation point, pixels outside the mid-tone latitude range are progressively desaturated as they approach the extremes. The darker curve in the _filmic rgb_ graph indicates the amount of desaturation that is applied to pixels outside the latitude range. Moving the slider to the right pushes the point where desaturation will start to be applied towards the extremes, resulting in a steeper desaturation curve. If pushed too far, this can result in fringing around the highlights. Moving the slider to the left brings the point at which color desaturation will start to be applied closer to the center, resulting in a gentler desaturation curve. If you would like to see more color saturation in the highlights, and you have checked that the white relative exposure in the [_scene_](#scene) tab is not yet clipping those highlights, move the mid-tones saturation slider to the right to increase the saturation.
highlights saturation mix/extreme luminance saturation/midtone saturation:
At extreme luminances, the pixels will tend towards either white or black. Because neither white nor black have color associated with them, the saturation of these pixels must be 0%. In order to gracefully transition towards this 0% saturation point, pixels outside the mid-tone latitude range are progressively desaturated as they approach the extremes. The desaturation strategy employed by *filmic rgb* has evolved over time and this section describes these approaches. Note that you can revert from the current version *v7* by selecting prior versions in the color science setting under the [_options_](#options) tab.

: Please note that this desaturation strategy has changed compared to previous versions of _filmic rgb_ (which provided a different slider control labelled _extreme luminance saturation_). You can revert to the previous desaturation behaviour by selecting "v3 (2019)" in the _color science_ setting on the [_options_](#options) tab. Since _filmic_ _v6_ and _v7_ use accurate gamut mapping to the output color space, the desaturation curve is removed and the extreme luminance desaturation becomes a method to control the bleaching of highlights.
The earlier versions of *filmic rgb* have direct controls over mid-tone saturation, which are described in the following paragraph. Versions *v6* and *v7* now use accurate gamut mapping to the output color space, so desaturation curve used in *v3* – *v5* was removed and the slider now controls the bleaching of highlights. In *v7* it is called *highlights saturation mix* and is called *extreme luminance saturation* in *v6*. Their defaults are set to 0 and it is recommended that saturation is handled earlier in the pipeline. A preset “*add basic colorfulness*” was added to the *color balance rgb module* for this purpose.

: This control is set to 0 by default and it is now recommended that saturation is handled earlier in the pipeline. A preset "add basic colorfulness" has been added to the [_color balance rgb_](./color-balance-rgb.md) module for this purpose.
In versions *v3 -v5* a darker curve in the filmic rgb graph indicates the amount of desaturation that is applied to pixels outside the latitude range. Moving the slider to the right pushes the point where desaturation will start to be applied towards the extremes, resulting in a steeper desaturation curve. If pushed too far, this can result in fringing around the highlights. Moving the slider to the left brings the point at which color desaturation will start to be applied closer to the center, resulting in a gentler desaturation curve. If you would like to see more color saturation in the highlights, and you have checked that the *white relative exposure* in the *scene* tab is not yet clipping those highlights, move the *mid-tones saturation* slider to the right to increase the saturation.

## display

Expand All @@ -235,7 +235,7 @@ target black luminance

: The target black luminance parameter sets the ground-level black of the target medium. By default it is set to the minimum non-zero value that can be encoded by the available number of bits in the output color space. Reducing it to zero means that some non-zero luminances will be mapped to 0 in the output, potentially losing some detail in the very darkest parts of the shadows. Increasing this slider will produce raised, faded blacks that can provide something of a "retro" look.

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

target white luminance
Expand Down Expand Up @@ -270,10 +270,10 @@ preserve chrominance (not available with color science _v7_)
: There is no "right" choice for the norm, and the appropriate choice depends strongly on the image to which it is applied. You are advised to experiment and decide for yourself which setting gives the most pleasing result with the fewest artifacts.

contrast in highlights
: This control selects the desired curvature at the highlights end of the _filmic rgb_ spline curve. The default setting (_safe_) is guaranteed not to over- or under-shoot but has quite muted contrast near white. Selecting _hard_ places a tighter constraint on the slope of the spline, which makes the curve sharper and hence introduces more tonal compression in the highlights. Selecting _soft_ loosens this constraint, resulting in a gentler curve with less tonal compression in the highlights.
: This control selects the desired curvature at the highlights end of the filmic rgb spline curve. The default setting (*hard*) places a tighter constraint on the slope of the spline, which makes the curve sharper and hence introduces more tonal compression in the highlights. Selecting *soft* loosens this constraint, resulting in a gentler curve with less tonal compression in the highlights. The *safe* setting is guaranteed not to over- or under-shoot but has quite muted contrast near white.

contrast in shadows
: This control selects the desired curvature at the shadows end of the _filmic rgb_ spline curve. The default setting (_safe_) is guaranteed not to over- or under-shoot but has quite muted contrast near black. Selecting _hard_ places a tighter constraint on the slope of the spline, which makes the curve sharper and hence introduces more tonal compression in the shadows. Selecting _soft_ loosens this constraint, resulting in a gentler curve with less tonal compression in the shadows.
: This control selects the desired curvature at the shadows end of the filmic rgb spline curve. The default setting (*hard*) places a tighter constraint on the slope of the spline, which makes the curve sharper and hence introduces more tonal compression in the shadows. Selecting *soft* loosens this constraint, resulting in a gentler curve with less tonal compression in the shadows. The *safe* setting is guaranteed not to over- or under-shoot but has quite muted contrast near black.

use custom middle-gray values
: Enabling this setting makes the _middle-gray luminance_ slider visible on the [_scene_](#scene) tab. With the current version of _filmic rgb_, you are advised to use the _exposure_ module to set the middle-gray level, so this setting is disabled by default (and the _middle-gray luminance slider_ is hidden).
Expand Down