To Convert a Selected Color Image to a Grayscale Image

1. On the ribbon, click Raster Tools tab Edit panel Process Image drop-down menu Histogram.

   The Histogram dialog box is displayed.

2. Select the Color to Grayscale 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.
3. Select a channel from which to apply the conversion values. You can select RGB, or you can select a single channel (Red, Green, or Blue). If you select RGB, then the values for red, green, and blue pixels in the image are added together and divided by three to achieve the grayscale value. If you select one channel, then the Color to Grayscale operation takes the value for that channel and uses it for the grayscale value.
4. 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 become more visible and the highest frequency values become truncated by the top of the window.
5. Select Apply to convert the color image(s) to grayscale.
6. Select 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 original settings.