Controlling Edits with Intricate Masks
In my earlier tutorial on Luminosity Masking, I introduced the use of this type of mask and briefly described using panels and sets of actions from developers to make them more accessible to us. Although I showed some screenshots of luminosity masks, I didn’t emphasize criteria when it comes to deciding when to use them. In this article I’ll take a look at sources for luminosity masks within Photoshop (free), and point to the more obvious times when you would, or likely would not, use a luminosity mask.
I’ve already discussed the luminosity mask you can make by Cmd/Ctrl-clicking on a channel thumbnail (the composite and individual color channels). This loads only a lights/darks luminosity mask, with the lightest lights by default fully selected, progressing through a range of ever darker grays until finally the blacks are fully deselected. One of the more common uses for this mask is to invert the mask when tinting a B&W photo, thus tinting the darker values the most, while leaving the lightest tones light and bright. Often tints applied to an entire image muddy the lights and reduce the full tonal range of the image—often effective when going for the aged and distressed look, but easily avoided when you want to tint a “clean” B&W.
Many people are not aware that Photoshop also includes a more precise method for generating a luminosity mask without using the Channels panel. When Photoshop updated the Color Range dialog, they added sliders to the Shadows, Midtones, and Highlights selections. The sliders now allow you to set a limit to the range of values considered Shadows, for example, and to decide how the selection will taper off. You’re targeting luminosity, not color, in your image, and generating the mask from that.
To know what tones to select, it helps to use the Info panel to read the values under your cursor before entering the Color Range dialog. After opening the dialog, select one of the three basic values and use the sliders to select the values you’d noted earlier. You can also look at the little preview in the dialog to help you visualize what is being selected. Unfortunately, I do mean “little” preview. There’s no preview in the document itself, which makes it more difficult to be precise about your selection visually. However, a Color Range mask does give you quite a lot of control over limiting adjustments to a specific tonal range.
Because choosing the right tonal range to target with a luminosity mask takes some practice, whether using Color Range, a panel such as Tony Kuyper’s, or directly using the Channels panel to create the mask manually, it helps to have a pretty good idea if your image is likely to benefit from a detailed mask. I’ve come up with three images that have a similar subject. They’re all a simple mountain range, but they vary in the distribution of values and their level of detail, as well as aesthetic considerations when editing the photos.
In the snowy mountain photo, there’s considerable detail and variation in values throughout most of the image. If I want to increase contrast through the midtones without blowing out the lights or blocking up the darks, a luminosity mask should be successful in limiting a simple Curves adjustment. No tedious hand painting is necessary.
In the photo with the bird where the mountain range is nearly all one value, it isn’t particularly useful to try to find a luminosity mask that affects only the clouds and mist, and another to affect the contrast in the mountains themselves. There’s so little contrast and detail to begin with, it’s easier to add a boost with a standard “S” curve, then broadly paint out the sky that has now been lightened more than desired. Another broad brush tones down the heavy darkening in the foreground mountain.
The third image of heavy fog weaving between the mountains is bit trickier. There’s certainly enough detail and distribution of values throughout the image to make us think of using luminosity masks. However, I think the image will be more successful, and have more depth, if the front of the range draws the eye with greater contrast, leaving the rest to recede. If I used a luminosity mask to target the midtones, all of the mountains would be affected. Since I only want to alter the lower third, it’s simpler again to apply a global contrast curve, then take a broad brush and paint out the effect on the rest of the image. You can do the same thing if you use a luminosity mask and paint on it to hide most of the effect. But why make an easy edit more complicated if you don’t need to precisely target a range of values?
Like many image editing features, luminosity masks are both easy to generate and very powerful when controlling what your adjustments affect. But also like many powerful features, it does take a bit of practice both in determining when to use them and what tonal range to use. Next time, I’ll demonstrate how using the TKActions panel helps when making those creative decisions.