How do I read a color histogram and why is it useful?

[Morne]

Pretty much like the title says.

In VFB and also in Photoshop and I geuss any other graphics program, you can view the histogram of your image. How do I read the thing and why is it usefull? How can I use it to know what is wrong with the colors in my image and then correct it?

[pixela]

It shows you the pure black(left) and white(right) and the range of values in your image in a graphical form.
You can see all your image values from the lowest value to the highest. You can see if an image is high-key or low-key from histogram even without looking at the image itself.