Using Levels to correct image contrast > Step 2

The Histogram, or graph portion, of the Levels dialogue shows how the picture's pixels are spread across the tonal scale.

Pixels in the center of the graph represent the image's midtones, those to the left are for darker tones, and those to the right are for lighter areas.

The three triangles below the graph represent the black, mid gray and white points of the image. These are called the input sliders.

The two triangles at the very bottom of the dialogue, under the gray scale, represent the black and white output points and so are called the output sliders.

Images with good contrast will contain a spread of pixels across the full range of tones.