Written by Steve Patterson.
In this Photoshop photo editing tutorial, we’re going to learn how to boost the contrast and color of an image using a little-known trick to select pixels based on their luminosity (lightness) values, which is officially known as “activating the luminosity mask”. Once we have our selection, we’re going to combine it with a layer blend mode to add more life to the image and give it a bit more visual snap.
Here’s the image I’ll be using for this tutorial. At the moment, the image is looking a little flat and the colors are a bit dull:
Here’s how it will look when we’re done:
Let’s get started.
Step 1: Ctrl/Cmd-Click On The RGB Channel To Create A Luminosity-Based Selection
The first thing I’m going to do is switch over to my Channels palette, which is grouped in beside the Layers palette:
Since my image is using the RGB color mode, and yours most likely is as well, the Channels palette is showing me my Red, Green and Blue channels. It’s also showing me what appears to be a fourth channel at the top named “RGB”, but it’s not really a channel. It’s just the composite of the Red, Green and Blue channels. If all this talk of channels is beyond your current Photoshop skill level, don’t worry. You don’t need to understand them for what we’re doing here.
All you need to know is that to select pixels based on their luminosity values, simply hold down your Ctrl (Win) / Command (Mac) key and click anywhere on the RGB channel in the Channels palette. I’m going to click directly on the thumbnail, but you can click anywhere on the RGB channel:
Once you’ve clicked on the RGB channel, you’ll see a rather crazy looking selection inside your image, as I have here:
What’s happened is that Photoshop has gone through the image and selected pixels based on how bright they are. Pixels that are pure white are selected 100%. Pixels that are pure black are not selected at all, and pixels that fall somewhere between white and black are partially selected at a percentage based on how close they are to white. In other words, what we’ve just done is selected the lightest parts of the image.
Step 2: Copy The Selection Onto A New Layer
First, switch back to your Layers palette. Then with the luminosity selection created, use the keyboard shortcut Ctrl+J (Win) / Command+J (Mac) to copy the selected pixels onto a new layer above the Background layer:
To show you what I mean about pixels being only partially selected, click on Background layer’s layer visibility icon (the eyeball icon) to temporarily hide it from view so that only “Layer 1″ is showing:
With the Background layer hidden, you can see that most of the pixels on “Layer 1″ are semi-transparent, and that’s because they were only partially selected:
Click once again on the Background layer’s layer visibility icon to bring it back into view.
Step 3: Change The Blend Mode For “Layer 1″ to “Overlay”
Now that I have the brightest parts of my image on a separate layer, I’m going to use them to boost the color and contrast of my image. To do that, all I need to do is change the layer blend mode of “Layer 1″ from “Normal” to Overlay:
If you find that the Overlay blend mode is too intense with your image, try Soft Light instead.
Here’s my image after changing the blend mode of “Layer 1″ to Overlay. Both the contrast and color have been boosted:
Step 4: Duplicate “Layer 1″ If Needed To Boost The Contrast And Color Even More
To increase the contrast and color in my image even further, I’m going to duplicate “Layer 1″ using Ctrl+J (Win) / Command+J (Mac):
With “Layer 1″ duplicated, the contrast and color in the image have been increased even further.
If you think your image could use even more of a boost in contrast, simply duplicate the layer once again. Or, if after duplicating “Layer 1″, you think the contrast is now a bit too intense, simply lower the opacity value of the duplicate layer until you’re happy with the results. I think I’ve increased my contrast a bit too much at this point, so I’m going to reduce the opacity of my duplicate layer to about 50:
Here’s my image after lowering the opacity of the duplicate layer:
My image is now looking a lot better than it did when I started, but there’s a small problem. By increasing the contrast, I’ve lost all the detail in the sky at the top of the image. In fact, the sky now looks almost pure white. I could just leave it like that, since the sky isn’t the main subject of the photo anyway, but since it’s so easy to bring the sky detail back, I’m going to do that next.
Step 5: Group The Luminosity Selection Layers
The steps on this page are optional and only apply if, like me, you’ve lost detail in part of your image after increasing the contrast and you want to bring the detail back.
In my case here, I have two layers that contain the pixels I selected with my luminosity selection:
In order to bring back the detail in the sky, I’m going to use a layer mask to hide the top areas of these two layers so that the sky in my original photo on the Background layer will show through. Since there’s two layers, I’m going to group them together and then apply the mask to the group, which is easier than trying to work with each layer separately. To do that, with the top layer selected, I’m going to hold down Shift and click on “Layer 1″ to select it as well, so both layers are selected together. Then I’ll use the keyboard shortcut Ctrl+G (Win) / Command+G (Mac) to place the two layers into a Layer Group in the Layers palette, which Photoshop names "Group 1":
To twirl the layer group open and closed, click on the small triangle to the left of the word “Group” and you’ll be able to see the two layers inside the group.
Step 6: Add A Layer Mask To The Layer Group
With both of my luminosity layers inside the group, I’m going to add a mask to the group itself by clicking on the Add A Layer Mask icon at the bottom of the Layers palette. A white layer mask thumbnail will then appear on the group:
Step 7: Paint With Black On The Layer Mask To Reveal The Detail In The Original Image
Now that I have my mask on the layer group, all I need to do is grab my Brush tool from the Tools palette, or press B on my keyboard to quickly access it. Then I’m going to press D on my keyboard to reset my Foreground and Background colors so black becomes my Foreground color. Then, with the layer mask selected, all I need to do is paint over the top of my image to hide the two luminosity layers in that area and reveal the sky in the original photo underneath them:
To quickly change your brush size as needed, use the left and right bracket keys on your keyboard. Continue painting with black on the layer mask until you’ve brought back the detail.
Once you’ve brought back any lost details in the image, you’re done!
Here’s my original once again for comparison:
And here is my final result after boosting the contrast and color using the luminosity mask:
And there we have it!