What is 'color balance,' which is important in photo editing?
When editing photos, you might sometimes find that the entire screen looks bluish, or that people's skin tones appear unnatural. 'Color balance' is crucial when correcting these color imbalances.
Color balance - Wikipedia
Color Balance in Digital Imaging | Nikon's MicroscopyU
https://www.microscopyu.com/digital-imaging/color-balance-in-digital-imaging
Surprising looks with white balance - Adobe
https://www.adobe.com/creativecloud/photography/technique/white-balance.html
Color balance is a process used in photo and image processing to adjust the overall intensity of colors such as red, green, and blue. Because it particularly emphasizes accurately displaying 'neutral colors' such as white and gray, color balance is sometimes also called 'gray balance,' 'neutral balance,' or 'white balance.'
The following is an example of how color balance adjustment can change the overall color tone of a photograph. The left half is the photograph as it was output from the digital camera, while the right half is a photograph that has been manually adjusted so that the gray areas appear as neutral gray. Photoshop's Levels adjustment was used for this adjustment.
The reason color balance is necessary is that the images recorded by cameras and film do not directly match the colors seen by the human eye. Image sensors and film have different characteristics than the human eye, and the way colors are perceived changes depending on the lighting at the time of shooting and the environment in which the image is viewed, such as the monitor or paper it is displayed on.
Even when photographing the same subject, the overall color tone of the photograph changes depending on the color of the lighting. Below is an example of a photograph taken with neutral lighting.
When you photograph the same subject with warm light, the whole image tends to have a yellowish or orange tint, like this.
When photographed in cool light, the entire photo tends to have a bluish tint.
Digital cameras offer white balance settings to compensate for these differences in lighting color. In addition to automatic white balance, some cameras allow you to select presets according to the shooting environment, such as sunny, cloudy, or incandescent. It is also possible to set a color balance that matches the lighting conditions by photographing neutral colors such as gray cards or white paper.
The following is an example of how changing the camera's white balance setting can alter the colors, even under the same neutral lighting conditions. First, here's an example shot with settings optimized for cloudy weather.
If you set it to be for incandescent light, the entire photo will have a bluish tint.
While slight discrepancies in the colors of trees, grass, and the sky are often unnoticeable, unnatural skin tone discrepancies can make a person appear unhealthy or sickly, making them particularly noticeable in portraits. The images below show examples of adjusting the color balance of portraits. You can see that not only the background and leaf colors but also the facial impression has changed between the 'Before' image on the left and the 'After' image on the right.
Color balance isn't always used solely to 'restore colors to something close to reality'; it can also be used to create atmosphere or impression by altering the colors of an image. For example, in the following photograph taken at Clifton Beach in Tasmania, Australia, the white balance has been adjusted towards warmer tones, creating a warm, evening-like atmosphere.
The following is a comparison of two photos of a skyscraper taken in quick succession within one minute of each other. The image on the left has a near-normal color balance, while the image on the right has a 'vivid' color balance due to an in-camera effect.
When an image appears to have a particular color bias, it's called 'color cast.' For example, if you photograph a white piece of paper under yellowish lighting, the camera will record the yellowish light reflected from the paper, causing the entire photograph to appear yellowish. Color balance involves estimating this color bias and then adjusting the red, green, and blue components to bring the image closer to a neutral state where white and gray appear more neutral.
Digital images often have red, green, and blue values (RGB values) for each individual pixel. Color balance adjustments involve, for example, strengthening the blue component in an image that appears yellowish, or conversely, suppressing the red or green components. In other words, the adjustment target is not just a part of the color in the image, but the RGB values of each pixel themselves.
Simple color correction adjusts the color tone by applying a certain multiplier to each RGB value, but RGB values are merely the strength of red, green, and blue in the image data and do not perfectly match the color changes that the human eye perceives. For example, even a slight increase in red numerically can make skin tones or grays appear significantly different to the human eye.
Color balance can be adjusted on the camera during shooting, or afterwards using image editing software. However, a 2004
A good example of what color balance means is the image of Mars taken by NASA's Mars rover 'Curiosity.' Below are three different color representations of the same image. The left is the unprocessed color sent back from Mars, the middle is the image after being calibrated to a natural color that is estimated to be close to 'what you would see if you were standing on Mars and looking at it,' and the right is the image after white balance processing has been applied to estimate the color of the Martian terrain as it would appear under Earth-like lighting. None of the three images is the 'correct color,' but rather they demonstrate that the color of an image changes depending on the purpose for which the colors recorded by the camera are displayed.
Color balance is not simply a process to 'return to real colors,' but rather a process to adjust the overall color of an image according to the lighting conditions during shooting, the display environment, and what you want to convey to the viewer.
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