| Using the Histogram
I'd be willing to bet that not many of you use the Histogram, know what it is, or what to use it for. Now you are going to find out. The histograms I am using here are from Photoshop, but Paint Shop Pro has a similar function.
|  | A histogram is a graphical representation of the colors in your image. A histogram displays the number of pixels at any given value from 0 to 255. You can use the histogram to analyze the color distribution of your image. It lets you see where the reds, blues, greens, and luminosity are. Here is a histogram from a fairly well balanced image:
The histogram is a graph. This one, and most of those I am using here, is a graph of luminosity values. A histogram can also graph the red, blue, or green values. The vertical axis of the graph represents the total number of pixels, the horizontal axis represents the pixel luminance value, with black (luminance value of 0) being on the far left and white (luminance value of 255) on the far right. Just from looking at this one, you can tell certain things. This image is not a dark image, as there is little information on the leftmost third. That is where shadows show on one of these. There is some very light or white color, the small spike near the right of the graph tells you that, but not a great deal of it. Most of the information in this image is contained in the center of the graph, so we can expect a normally balanced image with most of the detail in the mid color ranges.
Lets look at two more histograms:
High Key Image |
This is a good example of what we call a High Key image. The image is very bright and light in color. Notice how the histogram's curve jumps at the right. There is a small spike at the left end. This is the dark hair and the dark valve. Overall, most of the information in this image is contained in the upper third of the histogram. When you see this kind of shape; think bright, white image.
Low Key Image |
H ere is the opposite extreme. This is a Low Key gray scale. Most of the information here is in the shadows, and the graph reflects that, as the large spike at the left of the graph shows. There is very little information in the highlights, but if you look you can see a small spike at the very right of the graph.
OK. Now you can see what a Histogram does. So what? Well, lets go on to the contrast control and I'll show you what.
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