Color balance calculated incorrectly
Posted: Thu Oct 18, 2012 11:14 am
Hello,
I have been trying to correct the color balance on photo's but the result is not what I expected. It turns out this has to do with the way the color balance sliders work.
Color balance is a very wide concept, however, it often primarily refers to white balance. This is the most important color balance parameter. When no color shifting is performed, but only R, G and B values are linearly adjusted, there are 2 parameters that can be changed: black balance and white balance. When white balance is adjusted, black remains as it is, and the color of brighter colors is adjusted. When black balance is adjusted, white stays as it is, and the color of darker colors is adjusted. White balance is used to correct for incorrect light source colors for light that shines on the subjects. Black balance can be used to correct for a camera's non-zero value for black, or for when a secondary light source is giving an addition of light over the entire image (e.g. photographing through glass or haze).
The setting on the Image->Adjust->Brightness/Contrast/Gamma/Balance called Color Balance are neither of these. They perform a shift of the color values up or down only. So if we have 2 pixels, number one has a red value of 45 and number 2 has a red value of 210, and we move the slider upwards, they will both get the same amount of red extra. For example they would now be 45 + 22 = 67 and 210 + 22 = 232. This means if you want to correct the white balance of a photo, you also change black. If you add a lot of red and the dark background also becomes red. This is not good.
If you want the most basic and useful sliders there, then these should be white balance sliders. They would perform a multiplication only. If you want more, you may also want black balance sliders.
Regards,
Joris
I have been trying to correct the color balance on photo's but the result is not what I expected. It turns out this has to do with the way the color balance sliders work.
Color balance is a very wide concept, however, it often primarily refers to white balance. This is the most important color balance parameter. When no color shifting is performed, but only R, G and B values are linearly adjusted, there are 2 parameters that can be changed: black balance and white balance. When white balance is adjusted, black remains as it is, and the color of brighter colors is adjusted. When black balance is adjusted, white stays as it is, and the color of darker colors is adjusted. White balance is used to correct for incorrect light source colors for light that shines on the subjects. Black balance can be used to correct for a camera's non-zero value for black, or for when a secondary light source is giving an addition of light over the entire image (e.g. photographing through glass or haze).
The setting on the Image->Adjust->Brightness/Contrast/Gamma/Balance called Color Balance are neither of these. They perform a shift of the color values up or down only. So if we have 2 pixels, number one has a red value of 45 and number 2 has a red value of 210, and we move the slider upwards, they will both get the same amount of red extra. For example they would now be 45 + 22 = 67 and 210 + 22 = 232. This means if you want to correct the white balance of a photo, you also change black. If you add a lot of red and the dark background also becomes red. This is not good.
If you want the most basic and useful sliders there, then these should be white balance sliders. They would perform a multiplication only. If you want more, you may also want black balance sliders.
Regards,
Joris
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