Tonal Adjustment Tab (Histogram Dialog Box)

Use this tab to increase the detail in one part of the contrast curve without changing the detail in other parts.

RGB

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

Vertical Scale slider

Zooms in on the histogram. As you move the slider upward, the scale is increased so that low frequency values become more visible and the highest frequency values become truncated by the top of the window.

Contrast Curve Window

Displays the contrast curve. If you are using a fitted curve or piecewise linear curve, you can click and drag the curve's points and segments to edit the curve. You can also right-click to control the appearance of the grid, import and export curves, or reset the values. You can right-click on a point to delete the point.

Select Curve Type

Specifies the contrast curve representation in three ways:

• Gamma correction curves result in an exponential curve. It is defined by either specifying the single exponent (gamma) value or using an interactive slider.
• Fitted curves are drawn smoothly through points you specify. Points can be added or removed from the curve, or dragged to modify the shape of the curve.
• Piecewise Linear curves are constructed of points you add or modify. Each segment between points is a straight line instead of a curve.

Black

Specify a value in the text box, or move the black clipping slider, to adjust the point below which color values are displayed as black.

Gamma

Specifies the gamma value for the curve. The maximum value of 10 is the equivalent of moving the Gamma slider to the far left. The minimum value of 0.1 is the equivalent of moving the Gamma slider to the far right.

White

Specify a value in the text box, or move the white clipping slider, to adjust the point above which color values are displayed as white.

Import

Imports a curve as a Gamma Point List (*.gpl) file.

Export

Exports a curve as a Gamma Point List (*.gpl) file.

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, then all display-only adjustments are reset to the defaults.

Apply

Adjusts the contrast curve for the image and creates a new histogram that reflects the changes.

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.