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Click Raster menu
Image ProcessingHistogram.
The Histogram dialog box is displayed.
- Click the Threshold tab.
A preview of the image is displayed. If you selected more than one image, the histogram displays a composite of the images' values. You can view each image by clicking its name in the list.
Note: The preview reflects the image as it was read from the disk. If you have made any display-only adjustments to the image using the AutoCAD IMAGEADJUST command, then those adjustments are not displayed in the image preview. If you make adjustments to the image using the Histogram, the adjustments made with IMAGEADJUST are no longer applied to the image; instead the new settings are applied. - Drag the Threshold slider to determine which pixels are black and which pixels are white. All of the pixels to the left of the slider are black and all pixels to the right of the slider are white.
- To adjust the scale in the histogram window, move the slider up and down. Moving the slider up increases the scale such that low frequency values are more visible and the highest frequency values are truncated by the top of the window.
- Click Apply to convert the image(s) to bitonal image(s).
- Click Close to exit the Histogram dialog box.
If you are not satisfied with the results, you can use the AutoCAD UNDO command to restore the image to the original settings.
Note: When you use the Threshold command on a color image, AutoCAD Raster Design toolset first converts the image to grayscale, and then uses the grayscale value to create the bitonal image. This grayscale value is obtained by adding the values of the red, green, and blue channels in an image and dividing the value by three. If you want to have more control over which grayscale value AutoCAD Raster Design toolset uses to create the grayscale, then you can convert the color image to grayscale first, and then use the Threshold command on the grayscale image. For more information, see Converting a Color Image to Grayscale.