When reducing a monochrome image for display, simply using scaling algorithms like bilinear interpolation can cause the image to appear blurred, as shown below. This tendency is particularly noticeable in line drawings and document images.
Conventional scaling algorithm
To prevent blurring, it is possible to highlight the lines (foreground colors). This is a fast and effective method.
Highlighting the foreground colors
The highest quality method for displaying a monochrome image is to use grayscale. However, there were speed issues until about ten years ago. With the improvement in PC speed and increased standard memory capacity, grayscale display of monochrome reduced images now operates at a practical speed.
Monochrome grayscale conversion