The Shadows-Highlights tool is another useful photo editing feature making its debut in GIMP 2.10. With this tool, you can recover details in the shadows of your image while toning down overblown pixels in the highlights. Originally found in other Open Source photo editing software like Darktable, this feature was integrated directly into GIMP due to its popularity in the photo editing world.
To access the tool, go to Colors>Shadows-Highlights (shown in the image above). This will bring up the Shadows-Highlights dialogue box.
You should now see three sections, including Shadows, Highlights, and Common. The very first slider, labeled “Shadows,” allows you to adjust the exposure of the shadows. If you drag the slider to the right, which increases the value, the darker pixels in your image will become brighter. Using the photo above of my dog Harper as an example, you’ll see that the darker parts of her fur now become much brighter if I turn the value of the slider all the way up to 100. This will also reveal more detail in these pixels.
On the contrary, if I turn the value of the slider down to -100, the dark parts of her fur will get even darker and will lose detail.
For now, I’ll bring the value of this slider back up to 100 as it will help demonstrate how the next slider works.
The next slider is the “Shadows color adjustment” slider, which allows you to adjust the saturation of the color in the shadows of your image. We can really see how this feature effects the image with the Shadows slider turned all the way up to 100. By default, the Shadows Color Adjustment slider is set all the way up to 100. However, if I drag this slider down to 0, you will see the colors in the dark parts of Harper’s fur will become less saturated (they now look more like a light gray rather than a bluish gray).
If I bring this value all the way up to 100 again, you’ll see that the bluish color returns to the fur. So, in essence, this slider determines how much color is retained in your shadows after you have made adjustments to the exposure of those pixels. I will click the “Reset” button at the bottom of this dialogue box to reset the values in the Shadows-Highlights tool (the Shadows slider will revert back to 0).
The next slider is the Highlight slider, which performs the same tasks as the Shadow slider, but for the brighter pixels in the image rather than the darker. So, if I turn the Highlight slider up to 100, the bright pixels in our image get brighter (as you can see in the overexposed parts of the top of the image where the sun is shining).
If I bring the value of this slider all the way down to -100, the brighter pixels in the image will now get much darker – and you’ll start to see some details in the blown-out highlights that you couldn’t see before.
The next slider is the “Highlights color adjustment” slider, which allows you to add or remove saturation in the highlights of the image. By default, it is set to 50. If I bring the slider all the way up, you’ll see that the green pixels within the highlights get much greener (denoted by the red arrow in the image above).
On the other hand, if I drag this slider all the way down, the color in the highlights is removed and looks more like a black and white image (just in the area where the highlights are).
Once again, I’ll click the reset button to bring the settings back to their defaults.
The next section is the “Common” section, and the first slider is the “White point adjustment” which allows you to shift the white point of the image. By shifting the white point, you are determining the range of value of white pixels in the overall image. So, when you shift the white point to the right (in this example, increasing the value of the slider all the way up to 10), you are adding more white pixels to the image and thus making it brighter overall.
On the other hand, when you shift the value to the left (decreasing the value of the slider down to -10), you are decreasing the number of white pixels in the image and making it darker overall.
The next slider allows you to adjust the “Radius” of your effects, or the spatial extent of the effects. In other words, you can constrain your effects to smaller areas, or allow the effects to effect larger pixel areas. If I turn my Highlights value all the way up to 100 and drag the radius slider all the way up, you’ll see that the photo is very bright and almost has a hazy look to it. This is because the brighter pixels are spilling over into other pixels in the image, since the radius has less of a constraint on it.
If we reverse the radius slider by dragging it all the way down to 0, you will see that the photo is still brighter but it looks less hazy. The pixels that have been made brighter by increasing the highlights slider have been more constrained in the image and thus do not spill over into other pixels throughout the image. They are essentially more contained.
The next slider, the “Compress” slider, performs a similar function – though it contains your adjustments in either just the highlights or the shadows in order to preserve the midtones of your image. So, if you drag the slider all the way to the right (to a value of 100), it will contain your adjustments within the brightest pixels of your image (i.e. just the brightest highlights).
With the Compress slider still set at 100, drag your highlights slider all the way down, then all the way back up. You’ll notice that only the overexposed top part of your image is affected.
If you drag the compress slider all the way down to 0, playing with the highlights slider will now effect most of the pixels in your image.
I’ll click the “Reset” button to bring all the values back to their defaults.
Now that we’ve learned how each section performs adjustments on an image, and seen the extreme of each adjustment, I’ll now perform more moderate adjustments to the image to simply improve its overall appearance. As with most image adjustments, there is no one right way to edit the image with this tool, and it ultimately comes down to your own personal preferences.
For this image, I turn the shadows up a bit to recover some of the details in the darkest parts of Harper’s fur. Since I didn’t like the bluish color that was revealed from this adjustment, I turned the saturation of the shadows down to 75 (from the default value of 100). I then wanted to tone down the highlights a bit, so I brought the slider down to around -55, and turned the saturation of the highlights up to 70 (from the default value of 50). I then increased the white point to just under 1.0 (at .848), increased the radius to 120, and decreased the compression value to 43.03.