Well, histogram it’s a powerful tool in digital photography because it can tell you whether or not your image has been expose properly, it can tell us whether the lighting is flat or harsh.  It will not only improve your skills on editing on the computer, but as a photographer as well.

Let’s start from the beginning for a deeper and clear understanding. An image is composed from a combination of the primary colors: red, green and blue. Each color has different levels of brightness measured in values between 0 and 255. So a histogram is composed of the number of pixels on each level from 0 to 255. Here is an example on the left.

In fact the histogram represents the tonal range of an image (the black region). Every image has different tonal range so you could say that there is no ideal histogram. So you as a photographer should have to make sure that the histogram represents what’s in the picture.

Here is another example of how colors and different levels of brightness are represented in a histogram. This is just a representative example not an accurate one.

So how can we use these histograms?

Well there are 2 different types of photographs High key and Low key photographs:

1. High key images are the photos where the predominant colors are very bright and there’s a lot of white also. (for example when we photograph snow, or landscaped with a lot of snow in the frame)
2. Low key images are those images where there are a lot of shadow areas dark colors in general ( for example when you shoot  your room and the windows and outside of them are correctly exposed but the inside are pretty dark)

The ones in which we encounter the most problems are the High key photographs. Why is that? Because if you shoot the snow with your camera set on auto you will se that the snow will not look white but more of a grey. That’s because the camera tend to put all the brightness levels in the middle so that the exposure is correct. In this case all the whites from the snow will be dragged into the middle so the whites will become gray. That is why when you check you histogram in you camera you will know that on the monitor you photo will look grey so you bump up you exposure so the the picture will come overexposed a little but the white of your snow will become very beautiful.

Some examples of High Key and Low Key photos.

Increasing Brightness with any version of Photoshop until CS3 will add whatever you set the control at to every pixel in the image, shifting everything towards the right in the histogram. When are decreasing the brightness , all will be shifted equally darker. The tone of every pixel moved right or left equally with the same value, even when some parts of an image needed it more than others. The traditional version of Contrast adjustment was equally simplistic in how it operated, stretching or contracting contrast equally over the entire range of the histogram.

A photograph can contain 256 brightness levels ( from 0 which means pure black to 255 which means pure white). Let’s say that our photograph has a brightness level from 20 to 180. When we increase the brightness by let’s say 20, the new photo will have  a brightness level from 40 ( the old vale + 20) to 200 (the old value +20). So the Whole histogram is move to the right, when decreased move to the left.

So for the last two and a half years i only used Curves and/or Levels adjustments for increasing contrast and brightness. Now I saw that “Use legacy” option and started googling to see what exactly does and I found out that…

… since Photoshop CS3, they changed the algorithm of the “Brightness/Contrast” adjustment and put that option “Use legacy” so if you want you can still use the old one.

The new “Brightness/Contrast” algorithm operates proportionally, much as Levels and Curves do, rather than operating equally, in a linear way, on all pixels in the photograph. Pixels that need more of adjustment receive more of the effects of any change you make.

A simple change, but an amazing useful one since it turns a basically useless control into one that just might have a place in image editing for some people. Levels and Curves are still better since you have more control, but at least “Brightness/Contrast” won’t wreck an image if you use it. If you are in a hurry or for a casual image editing, it can in fact work quite well now.

Here’s an example with an increase of brightness by 40 on both photographs.

Here is the original photograph (Shot in Dobrogea, Romania)

Adjusted with the new Brightness/Contrast                      Adjusted with the old Brightness/contrast