Development / Contrast
Actions
- contrast/new : Creates a new contrast group for hi/lo contrast adjustment.
- contrast/lo * [l] : Converts the currently selected Adjustment Layer into a Curves Adjustment Layer that adjusts lo contrast by * levels.
- contrast/hi * [l] : Converts the currently selected Adjustment Layer into a Curves Adjustment Layer that adjusts hi contrast by * levels.
The set of contrast actions for FFDD6 provides a method to adjust photo contrast in a Linear colorspace.
How to Use
With the new Linear editing of FFDD6, under nearly all conditions an image only needs one overall contrast adjustment after all other processing is finished (so the contrast adjustment should be the top layer). To add a contrast adjustment, first select the top layer of the image, and click the contrast/new action button.
This will create a new layer group containing two adjustment layers.
Given the low contrast of an un-developed raw file such as this.
To adjust the contrast, make adjustments to the high and low contrast settings in the contrast layer group. First select the contrast/hi layer.
Then click one of the contrast/hi action buttons (which are all blue).
Which will result in the correct settings being applied to the adjustment layer.
Then do the same for the contrast/lo layer, except this time use one of the contrast/lo actions (which are all green).
And here is the result.
If your first guess on contrast is incorrect, simply individually re-select the hi and lo contrast adjustment layers and re-run the actions until the proper setting is found. Also it is a good idea to keep both the hi and lo contrast settings matched to the same number. So if using +28 for the hi setting, use +28 for the low setting as well.
Technical Details
Simply adjusting contrast using a single curves adjustment layer would seem like the ideal method to adjust contrast. However when editing in a Linear colorspace, there are some serious problems with this method.
First, when colorspace Gamma is set to 1.0 (ie Linear), perceptually the middle tone is right around level 47 (out of 256 levels). So while adjusting the highlights is easy, adjusting the darks is near impossible with Photoshop's limitation of not allowing 16-bit levels adjustments. To get around this, FFDD provides separate curve adjustment layers, using the screen and multiply blending modes to get around the 8-bit levels limitation, allowing for much more precise adjustments.
Second, small consistent contrast adjustments require adjusting all points along a curve, and are near impossible to consistently reproduce in the same way each time. The FFDD actions remove the need to do hand curve adjustments, and simply allow for 24 individual levels of contrast, which always provide the same result.
Because of the screen and multiply blending modes, these new FFDD6 Linear contrast curves do not look like standard S curves. However they function as correct S curves. Here is a shot of the curves for the most extreme high and low contrast adjustments,
