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Chapter 6. Understanding Curves > The Idea Behind Curves

The Idea Behind Curves

Because the Curves dialog box allows you to adjust every shade of gray in an image independently of the others (256 in all), it works quite a bit differently from the other adjustment tools. To get a clearer picture of what Curves does, let's construct our own Curves dialog box from scratch, using something you're already familiar with: the plain old vanilla bar chart. You know what I'm talking about—those wretched bar charts that can't be avoided in magazines, brochures, television, and pretty much everywhere you look. Now we can finally put one to good use by using it to help us understand Curves.

What if you create a bar chart that indicates how much light your monitor uses to display each color in an image? This bar chart would be just like any other that you've seen, where taller bars mean more light and shorter bars mean less. You could show the shade of gray you are using below each bar, and then draw a line from the top of each bar over to the left so you could label how much light is being used for each shade. I think you'd end up with something that looks like Figure 6.12. Or you could just as easily change the chart to indicate how much ink your ink- jet printer would use to reproduce the image. Now that we're talking about ink, short bars would mean less ink, which would produce a light shade of gray, and tall bars would mean a lot of ink and would produce a dark shade of gray. To make the change, all we'd have to do is flip all the shades at the bottom of the graph so the dark ones are below the tall bars and the bright ones are below the short bars. The result would look like Figure 6.13, right?


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