You can adjust the brightness of shadows, highlights, or midtones by using the Levels command. Brightness values range from 0 (black) to 255 (white). For colored pixels, brightness is the brightness value in each color channel.
The Levels command works with all image modes except Black & White and Indexed.
You can save Levels settings on disk to use again. For example, after correcting a scanned photo, you can save the settings and use them to correct other images scanned from the same source.
Choose an individual color channel or the composite channel.
Type values in the Input Levels boxes or drag the slider under the histogram to set the minimum input level, midtone ratio, and maximum input levels.
Type values in the Output Levels boxes or drag the sliders to set the minimum and maximum output levels.
The histogram graphs brightness levels for the selected channel.
Click Auto for Canvas X Draw to map the darkest values in the selection to black and the lightest value to white.
Click the Set White Point eyedropper tool. Click in the image to pick the values you want to assign to the lightest area in the image. Click the Set Black Point eyedropper tool. Click in the image to pick the values you want to assign to the darkest area in the image.