Contrast-Stretch by Flo

An Image Magick Tute by Flo

Look under the Enhance tab to find Contrast-Stretch. This tool is very useful for increasing the contrast in a high key image which has little contrast. But this tool also gives no control over the mid-tones value. Sometimes Sigmoidal Contrast gives better results, because it allows control over the middle tone range, too.. So try both before deciding.

Mr. Cristy's instructions: "Contrast-Stretch: improve the contrast in an image by `stretching´ the range of intensity values. A good starting point is a 1% black and white point (e.g. 1%)."

So we use percents. I have used percents up to 50, but never higher. We don't want to blank out the lightest tones, nor do we want to block up (blacken) the darkest ones, if possible. In my experience, 10 percent gives great results.

When making the title image above, I used Contrast-Stretch @ 10% to make the right image from the left one. That was more than adequate.


Original	Con-Stretch @ 10%

Original	Con-Stretch @ 10%

Five ways to use to get more contrast and more color saturation in an image:

Enhance/SigmoidalContrast;

Use several Composites, one after the other, or several of the same Composite;

Enhance/Saturate;

Enhance/Contrast-Stretch (this tute);

Enhance/Level (Flo's tute coming)
- see Stranjer's Level tute
Tiger Lily's Level tute
Flame's Level tute

Each way produces different effects, so choose the way that gives you the most pleasing results.