When editing pictures you should first consider white balance and contrast. White balance is normally what you ought to fix first, then contrast.White balance should be addressed before contrast because color contrast can not be set properly if the image has a color cast.
White balance addresses the color of the illumination within the photograph and sets white as a goal. White balance applications attempt to correct the color of the illumination to white and to do that, the application needs some neutrals in the picture to calibrate the suitable correction tone from. The whites can for example be a white wall or a sheet of paper or a dedicated white card. The grays are more difficult to find in real life, so one can use a dedicated gray card.
White balance software comes in two varieties: automatic and manual. The manual mode usually consist of a single temperature slider for adjusting the light cool or warm. This is OK for incandescent light, but not for fluorescent light or mixed light. When converting RAW images, one usually has a temperature slider. One can also have three color sliders for red, green and blue. Color sliders can somewhat correct fluorescent light and mixed light, but the problem with using color sliders is that the black and the whites usually get a bad tone. Software with an auto option usually need neutrals in the image to work well, such as a gray-card or white-card. There are a few apps that can dispense with the neutrals, but usually neutrals are needed.
Contrast comes in three varieties: contrast of hue, brightness and saturation. Very few applications have more than a single slider for contrast, that addresses all three kinds of contrast at once. However, a single slider for all three is unsatisfactory since the result is usually over saturated and gaudy. The best software has two contrast sliders: one for luminance contrast and one for color contrast.
The standard way to manipulate contrast is simply by changing the difference between the individual red, green and blue values and the middle value (128); like this: R= (R-128) * contrast + 128; and likewise for green and blue. This method is not suitable for very dark or very pale images. What if the image is very pale or very dark? In that case you can't use 128, but have to use the average of the individual channels in the image, like this: R=(R-RAverage)*contrast+RAverage. And so on for G and B. Using 128 attempts the same and merely assumes the picture has a full range of brightness values, in which case the average will be 128.
If the darkest and brightest areas are not black and white a different situation arises. In that case one should be able to expand the brightest range to reach black and white. This is essentially what levels adjustment does. One can do this with Photoshop's levels adjustment like this: First convert the image to Lab mode, select the L channel only and run auto levels on that. Then convert back to RGB mode.
White balance addresses the color of the illumination within the photograph and sets white as a goal. White balance applications attempt to correct the color of the illumination to white and to do that, the application needs some neutrals in the picture to calibrate the suitable correction tone from. The whites can for example be a white wall or a sheet of paper or a dedicated white card. The grays are more difficult to find in real life, so one can use a dedicated gray card.
White balance software comes in two varieties: automatic and manual. The manual mode usually consist of a single temperature slider for adjusting the light cool or warm. This is OK for incandescent light, but not for fluorescent light or mixed light. When converting RAW images, one usually has a temperature slider. One can also have three color sliders for red, green and blue. Color sliders can somewhat correct fluorescent light and mixed light, but the problem with using color sliders is that the black and the whites usually get a bad tone. Software with an auto option usually need neutrals in the image to work well, such as a gray-card or white-card. There are a few apps that can dispense with the neutrals, but usually neutrals are needed.
Contrast comes in three varieties: contrast of hue, brightness and saturation. Very few applications have more than a single slider for contrast, that addresses all three kinds of contrast at once. However, a single slider for all three is unsatisfactory since the result is usually over saturated and gaudy. The best software has two contrast sliders: one for luminance contrast and one for color contrast.
The standard way to manipulate contrast is simply by changing the difference between the individual red, green and blue values and the middle value (128); like this: R= (R-128) * contrast + 128; and likewise for green and blue. This method is not suitable for very dark or very pale images. What if the image is very pale or very dark? In that case you can't use 128, but have to use the average of the individual channels in the image, like this: R=(R-RAverage)*contrast+RAverage. And so on for G and B. Using 128 attempts the same and merely assumes the picture has a full range of brightness values, in which case the average will be 128.
If the darkest and brightest areas are not black and white a different situation arises. In that case one should be able to expand the brightest range to reach black and white. This is essentially what levels adjustment does. One can do this with Photoshop's levels adjustment like this: First convert the image to Lab mode, select the L channel only and run auto levels on that. Then convert back to RGB mode.
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