Why do White balance?

Why do White balance?
Almost all digital cameras will be able to white balance the camera quality. Provides functionality for users to adjust multiple choice. This article discusses the principles and use white balance to get the correct color images come out properly as it should be the most
Why do White balance?
Because of our human ability to adjust the color perception by changing lighting conditions such as If we look at white paper under the sun. We can see that the paper is white. When we move to look the same sheet of white paper umbrella at first we could see that the paper in a different color from the color of the sun because the light has changed. But a few minutes later. Our eyes and brain. Adjust the perceived relative to the lighting conditions to see that now. As a result, we see the white paper. This phenomenon is called chromatic adpatation but because the digital camera with CCD is a sensor (compared with the bell in the eye) can not modify the sensitivity color like the eyes when we are shooting white paper under daylight. Suppose that the RGB from the camera as R255, B255, G255 (if the RGB pixel any equal pixels that are white, black, achromatic), but if we shoot white paper the same sheet with light tungsten will. the R255 B180 G200 shows that the image white paper that will stand แdongๆ orange in order to make photo paper white becomes white Dog requires software to help make up the RGB color white from the light source with a different color. each other to be the equal of any such action is called white balance adjustment by adjusting the white balance is not made only to pixels that are part of the picture, but the white do with Every pixel of the image.
Examples of white balance.
In general, the camera will make automatic white balance (Auto WB), however, are already adjusted to such a limit. Solution is only a certain level only. Observations from the three images below. Auto WB is taken with the Canon Powershot G1 camera images under different lighting conditions, images are left. daylight (6500K) is the central image coolwhite (4800K) and the right image. tunsten (illuminant A, 2856K).

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 Can see that the color chart image taken under daylight lighting and color coolwhite correct. But the image under fire Tungsten color distortion to the red rather In order to clear up the Ying of the Auto WB, try to compare Three images below the three pictures above. Picture below was taken by the same camera but the camera is set WB to daylight.

 

We can see that the left image taken under daylight lighting for accurate color. Images taken under a light coolwhite red color to the slightly distorted. And pictures taken under tungsten light will be very distorted colors. And distortion than images shot with the Auto WB herein show that the operation of the Auto WB resolve color images with accurate colors even more. But is limited in general to Auto WB will work well in the range of 4800-7500 K, if the light source color temperature is more or Less than this. Camera will not modify the color out. The camera with a professional or semi-professional functions will allow users to manually adjust the WB (called the Custom WB) by ordering the camera configuration at the WB in black and white. Don White adjustment that is most convenient. Because if the light source has already distorted the RGB color white is the most different. Picture below shows. Comparisons when setting the custom WB image under white light of daylight coolwhite and tungsten, respectively.

 

From the image above to see the image in the gray bar. Colors are more accurate than Ying Auto WB adjustment model, however, will see that part. In orange and red. Photo Tour of the fire station also has a spring color that express poorly. This is the limit between the color of the object and the color of the light sources. And that can not be corrected. In addition to setting a custom WB, white, users may adjust the location of a gray or black optional. However, errors may have more than white. Picture below shows. Comparisons when setting the custom WB White (picture left), gray bar, third from left (middle picture) and black (right image).

 

Because the color chart is created well in color, so to make custom WB on the gray or black and white images should have the same color. But Denis' images made ​​WB the middle gray will see that the picture is distorted to the blue color. Cause of the distortion caused by such objects as targets for the WB do have other colors come from contamination. If observed from the first image on the left to see that good. Gray bar at the Three red contamination from reflections of the base paste. When Gray is not gray generous, if we set the WB to the right of all the colors of the image with distortion.

Therefore, the best WB setting is still setting a custom WB, but also cautions that the object is a target of the WB should be set as an object that is a true black and white.