What Causes Color Banding?
An image needs adequate bit depth to sustain various and sufficient shades of color for a smooth transition between colors. If there isn’t enough tonal range to represent, from brightest to darkest, the different colors (your bit depth is too low), it can cause color distortions rather than a smooth gradation between color shades.
The number of bits gives you the tonal range. For example, an 8-bit photograph will have 256 tonal values per color, while a 16-bit one has 65,536. Sometimes fewer bits are enough, while you’ll need more bits and tonal range at other times.
Keep in mind that today’s technology (your digital camera and monitor) works with three color channels: red, green, and blue.
Multiply 256 tones per 3 colors, and you get 16.7 million colors. While that is sufficient for a detailed image area, it might not be adequate for a seamless area with too many variations of one color. To obtain a smooth transition in that area and avoid color banding, you need a larger tonal range.
This means shooting in uncompressed RAW, which holds far more information than shooting in JPG.
If an image has a good balance of tone values, you can adjust the curves or brightness to reach its maximum and create a greater range within the gradient. However, the quality of an image matters as well. If the resolution is too low or compression has caused tonal values to be diminished, you’ll likely see some degree of color banding.
How to Test for Color Banding
You might not notice color banding until you hit save and print. However, you can check for it beforehand by doing a color banding test.
In Photoshop, open the Channel panel from the Windows menu.
It should pop up on the right side of your screen, and four channels will appear.
The first channel is RGB, which puts together the other three, allowing you to see the image in full color.
The three other channels form the picture, one for each color: red, green, and blue.
You can check for banding by activating each color individually by clicking on the eye icon next to each one.
If you’re working with a JPG, you can sometimes see color bands appear while you’re saving the file.
Try zooming into any area with a broad swath of one color, like the sky.
Save the file.
In the Preview option, begin lowering the quality of the file while watching to see if any banding shows up.