The black-normalize option increases the number of black pixels in a grayscale image by a specified percentage in order to sharpen the contrast between its black and white colors. Use this option in conjunction with the white-normalize option when encoding grayscale images that contain text and backgrounds of similar hues. For example, dark gray text on a light gray background can be converted to black text on a white background, thus improving its readability.
Assign values to the black-normalize option as described in the table below.
Supporting command:
documenttodjvu
Value |
Description |
-1 |
Default. Attempts to auto-normalize the separation between an image's black and white colors. |
0 |
Does not change the separation between an image’s black and white colors. |
1-100 |
Increases the number of black pixels in the image by this percentage. For example: documenttodjvu --black-normalize=50 survey.jpeg survey.djvu This use of --black-normalize increases the number of black pixels in the output image, survey.djvu, by 50 percent. |