Hans D. Baumeister

Hans D. Baumeister

Bizarre phenomenon with flatbed scanner

This is really weird. I wanted to scan a picture my daughter had made. Not a problem, after all, I have my trusty old Epson Perfection 1640SU that works perfectly with Apple Image Capture (without loading a driver, mind you). I’ve been using it to scan in old photos and - since I have a lightbox for it - old negatives.

The image quality off this device is absolutely sufficient for what I’m trying to do, and the images made are very clear and clean.

Up to now.

I scanned the picture in full color and looked at the result on the screen. Weird. Bluish lines coming from the drawing. Maybe the scanner wasn’t warmed up properly, though I don’t understand why this would be the outcome from a cold lamp... usually, you get a magenta tint to the entire scan if that is the case.

So I scanned it again. Same effect.
I scanned the white background of the inside cover, to make sure something wasn’t coming through.
Nothing. A plain white JPG.

Okaaaay... so I physically turned the picture by 180° and scanned again. If it was something coming from the paper, it should produce the identical result, just turned by 180° is the JPG. While the effect was there again, the fuzzy blue lines looked different:


What you see on the left is Image Capture with the scanned image of the butterfly looking left. To the right of that is Preview with the previous scan (where the butterfly looked right) but turned 180° to make the two point in the same direction.

You can see that the odd blue lines are similar, but certainly different, between the two scans. So my first guess, that perhaps the scanner is picking up something in ultraviolet that the human eye can’t see, such as finger grease, doesn’t seem to be the case here.

I’m really confused as to what this could be... perhaps there is a static buildup within the CCD due to the high contrast between color and white that is discharging somewhere else and causing the scanner to pick up a bit that isn’t on the paper? I haven’t the faintest idea.