All image-manipulation software allows you to adjust the overall colour of an image.
Most also offers Levels and Curves control.
In powerful software, such as Photoshop, you have separate tools for controlling an imaged hue and saturation, as well as others for replacing specified colours.
Color Balance control This control makes global changes to the standard primary or secondary hues in an image.
In some software, you can restrict the changes to shadows, highlights, or mid-tones.
This control is useful for making quick changes to an image that has, for example, been affected by an overall colour cast.
Levels control This can be used to alter colour balance of an image by adjusting separately the Level in each colour channel.
It is similar to the Color Balance facility, but it provides you with greater control over brightness.
The great advantage of Levels is that, in most software, settings can be saved and reapplied to other images.
Curves control This controls the tonal reproduction of image brightness values, represented by a curve running from the lightest to darkest values.
It can do everything the Levels control can, but with more precise location of where changes in tonal value occur.
By carefully manipulating the curves in separate colour channels you can change the colour balance to counteract irregularities in colour reproduction in both film-based and digital originals.
For example, you can decrease the blue content of shadows, to remove cold-looking tones, while leaving the rest of the imaged colour balance untouched.
White point A quick method of working when you wish to colour-correct an image is by deciding which part of the picture you want to be the white point - that part you want to be seen as pure white.
You then use the Highlight Dropper tool, which is commonly available in image-manipulation software as well as part of scanner drivers, to select that area.
If the white point needs to be corrected, the whole image will change in tonality (it is said to be mapped to the new white point) to reflect the fact that your selected area is now the "official" pure white point.
This, like all colour-correction methods, works only if the image has no strong colour cast.
If it has, then more drastic measures may be needed.
Most also offers Levels and Curves control.
In powerful software, such as Photoshop, you have separate tools for controlling an imaged hue and saturation, as well as others for replacing specified colours.
Color Balance control This control makes global changes to the standard primary or secondary hues in an image.
In some software, you can restrict the changes to shadows, highlights, or mid-tones.
This control is useful for making quick changes to an image that has, for example, been affected by an overall colour cast.
Levels control This can be used to alter colour balance of an image by adjusting separately the Level in each colour channel.
It is similar to the Color Balance facility, but it provides you with greater control over brightness.
The great advantage of Levels is that, in most software, settings can be saved and reapplied to other images.
Curves control This controls the tonal reproduction of image brightness values, represented by a curve running from the lightest to darkest values.
It can do everything the Levels control can, but with more precise location of where changes in tonal value occur.
By carefully manipulating the curves in separate colour channels you can change the colour balance to counteract irregularities in colour reproduction in both film-based and digital originals.
For example, you can decrease the blue content of shadows, to remove cold-looking tones, while leaving the rest of the imaged colour balance untouched.
White point A quick method of working when you wish to colour-correct an image is by deciding which part of the picture you want to be the white point - that part you want to be seen as pure white.
You then use the Highlight Dropper tool, which is commonly available in image-manipulation software as well as part of scanner drivers, to select that area.
If the white point needs to be corrected, the whole image will change in tonality (it is said to be mapped to the new white point) to reflect the fact that your selected area is now the "official" pure white point.
This, like all colour-correction methods, works only if the image has no strong colour cast.
If it has, then more drastic measures may be needed.
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