Why is a checker board type pattern appearing in my Greyscale scan?

Question

Visioneer One Touch 6600usb scanner.

I have a black and white picture that I am attempting to scan. I have scanned others with no problem. However, this on has a checker board pattern.

I have tried various dpi and contrast settings but they just seem to make things worse than the default setting of 300 dpi.

Any ideas?

OS is Windows XP Pro, SP3.

Answer 1

Usually because the original that you are scanning uses halftoning (e.g. newspaper or magazine photos) or dithering of some sort.

When you scan such an image at a resolution and orientation that differs slightly from that used in the original you get a kind of Moiré interference effect.

The effect should disappear if you scan at a much higher or much lower resolution. Instead of 300 dpi, try 4800 dpi or 30 dpi.

See discussion in various places.

Some scanners have a descreening option to combat this.