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Compressing the color channels

We need to edit both the a and b channels with the same settings so that the colors look balanced. First, we'll start with the a channel. In the channels palette, click on the a channel.

Once you have the a channel selected, your image should look like a low-contrast gray image. We can't do any color editing without seeing what the colors look like, so to solve this issue, click on the visible option on the left of the Lab channel. Once you do that, there should be four eye icons that show up beside the channels.

The secret to increasing the saturation is to increase the contrast of these color layers. By increasing the contrast, the colors will look more vivid. While increasing contrast may result in clipped details where some of the lighter or darker details may disappear, but once you open the Levels tool to compress the histogram, you'll see that there is a lot of room to adjust the colors. Press Ctrl+L or choose Image > Adjustments > Levels to open the Levels tool. In the Levels tool, move the black and white input slider towards the middle. They gray input slide should still be in the middle. As you move the two sliders, look at the image preview to gauge/measure how much saturation you are applying. The colors may look slightly off, but focus on the saturation. Once we repeat this step for the other channel, the colors will look fine. When you're done, click OK.

Now we need to repeat the same process for the other channel so that all the colors have the same vivid look. In the channels palette, select the b channel. The four eye icons should still be visible but if it isn't, simply click on the visible option located on the left of the Lab channel and the four eye icons will appear.

Now repeat the same process with the Levels tool that we did earlier. Press Ctrl+L or choose Image > Adjustments > Levels and move the black and white input slider closer towards the middle to compress the histogram. The settings should be the same as the ones you used earlier as a start. Once you have it set with the same settings as the other channel, you can adjust the sliders to alter the intensity of the colors for this layer. For example, if you don't want these certain colors to be that vivid, simply move the two input sliders further apart to reduce the compression of the colors.