Histogram

Histogram and digital photography

The histogram of a digital photo shows you if a photo is well balanced, if it is overexposed or if it is underexposed. But it can also help you to correct a bad balanced photo or one with a color cast.

If the curves are much higher in the left part, the photo will look rather dark. If they are much higher in the right part, the photo will look rather light. It does not always mean that it needs to be corrected. Just may be...

If one color passes over the other colors towards the right, it means that the photo may have a color cast.

A few examples of histograms:

	This histogram is well balanced. But some red color cast is visible.
	This is the histogram of an underexposed photo. The curves stick to the left edge. The right part of the histogram is nearly empty. In the underexposed area of the photo, details will be missing. They can not be brought out by making the photo lighter through some strong gamma correction or brightness correction.
	This is the histogram of an overexposed photo. The curves stick to the right edge. The left part of the histogram is nearly empty. In the overexposed area of the photo, details will be missing. They can not be brought out by making the photo darker through some strong gamma correction or brightness correction.

A bad balanced histogram does not always mean that the picture is bad! Many photos are made consciously to be underexposed (e.g. sunsets).

At the page Gamma Correction, you can read how the assistance of an histogram can help you to easily correct a bad balanced digital photo through the approach of levels adjust combined with gamma correction.

Below, you can read how the assistance of an histogram can help you to correct a color cast.

The manual RGB correction with histogram assistance

Basically, the function needed to correct color casts is some kind of RGB adjust that most photo editors implement (RGB means red green blue, the basic colors of active color synthesis). But with a simple manual RGB adjust, you will try forth and back and hardly find the right setting.

For the ease of use of a manual RGB adjust, you need an indication telling you how much one (or two) of the basic colors must be shifted. A small histogram of your photo will give you a good indication.

For example, if any part of your photo should be white or neutral grey, but it is not, you will see some red, green or blue peaks in the histogram that are close together instead of overlapping each other. Photo correction of color casts means just to shift one or two basic colors until the peaks overlap.

Photo-Brush

with its function "white balance compensation" shows such an histogram and you will see the histogram peaks sliding away as you move the color cursors.

Example:

before	after
before
after

Digital photo enhancement of color casts through a manual RGB correction with histogram assistance gave me very good results.

Nevertheless, Color Washer.

with its 5 auto modes and the possiblity to retouch slightly manually is faster and more convenient. It is faster because you will use its excellent contrast correction in the same walk. Instead of going through two successive steps and using two separate functions, you will correct a color cast and improve the exposure and contrast through one single step.

Color Washer shows also an histogram of your photo. More about Color Washer at the page Digital Photo Enhancement.