Start with an image on the worktable.
Click Histogram in the ribbon, and then click the Equalize tool in the palette to display the Channel Mixer dialog.
Equalize Histogram is a method of increasing the contrast in an image. You may find it useful to use in images that are over or under-exposed. Just as the name implies, it spreads out or levels off the intensities, or the spikes in the histogram, which allows the lower contrast areas to gain a higher contrast.
The weakness of this method is that it is across-the-board so it may result in producing unrealistic effects in photos. The strength of this method is that it can produce wonderful contrasts in localized parts of an image that could then be used for creating symmetries and other beautiful patterns to print on fabric.
The Equalize Histogram dialog lets you select the color space to equalize. The possible values are:
- RGB – Linearizes the number of pixels across the RGB color space. Each channel (red, green blue) is done separately.
- YUV – Linearizes the number of pixels across the YUV color space. This usually gives the best results because YUV incorporates human perception like in your color television.
- Grayscale – Linearizes the number of pixels per gray level in a gray level representation of the image.
Click IMAGE > Histogram > Adjust. Notice the histogram has severe spikes and drops off to the right indicating there are very few light pixels.
Click Equalize in the Histogram Options palette.
Open the adjustment again, by clicking Adjust in the Histogram Options palette. The equalized histogram now extends more evenly to both ends of the graph.