Equalize Tab (Histogram Dialog Box)

Use this tab to maximize the details in an image that has a large percentage of pixels that are approximately the same color. Equalization changes the darkest pixels to black and the lightest pixels to white and then reassigns the remaining pixels to use all of the colors in between. This is also known as a non-linear contrast stretch.

You can equalize a grayscale image or a color image. When you equalize a color image, you have the option of selecting which color channel you want to equalize. For example, if you have an image that is composed of mostly red shades, then you can select the red channel and equalize only that channel, spreading out the red values so there is greater contrast.

Equalize Tab Options

Index

Displays the intensity of each shade on the histogram (0 to 255). For a grayscale image, all channels have the same values. If you select the Red, Green, or Blue channel when you are equalizing a color image, the index number is the intensity of that color within a pixel.

Freq

Displays the number of pixels within an image of a selected Index value.

Apply Changes To

• Entire Image. Applies the changes to the selected image.
• Sub-Region. Applies the changes to the sub-region only.

Sub-Region Options

Contains palette options for sub-regions associated with an Index Color (8-bit)

• Retain Current Palette. Applies your changes to the sub-region by mapping to the closest colors from the current palette. This option maintains the current palette and does not affect pixels outside the selected region.
• Rebuild Palette With All Colors. Creates a new palette to best accommodate all colors in the entire image. Because this image changes the palette, pixels inside and outside the sub-region may be affected by this option.
• Rebuild Palette With New Colors. Also creates a new palette, but this option guarantees that colors in the sub-region are included in the palette by giving preference to those pixels over pixels outside the sub-region. Because this image changes the palette, pixels outside the sub-region may be affected by this option.

Apply

Equalizes the image and creates a new histogram that reflects the changes.

RGB

Specifies the color image. You can select the Red, Green, or Blue channel, or the combined RGB channel. For a grayscale image, you can only select the RGB channel.

Preview

Displays a preview of the image showing the modifications.

Click an image name to view the preview for that image. Histogram changes apply to all images you have selected, not just to the image that is currently previewed.

This preview does not show any display-only adjustments you may have made to the image using the AutoCAD IMAGEADJUST command. If you apply changes to the image using the Histogram command, then all display-only adjustments are reset to the defaults.