Why do JPEGs show horizontal colored bands after copying from a card reader?

Asked 3/20/2014

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Some JPEG photos looked fine on the camera, but after copying them to my computer they showed horizontal colored bands and shifted image sections. I ruled out other causes and found the problem only happened with one USB card reader; using a different reader fixed it. The reader was labeled USB 3.0, while the laptop only has USB 2.0. How can images become corrupted during the copy process, and what likely caused these artifacts?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

12y ago

2 Answers

5

The image was corrupted by random bytes of information being lost in the data transfer. You can tell because each time information is lost, the image shifts (because pixels end up missing as it fills each line). It's also not an even number of pixel information since some of the times that information is lost, it causes the color information to get shifted by a set of values (red become blue, blue becomes green, green becomes red, etc) This is why on some of the shifts you get a sudden color change.

So instead of something like this:

111222333
444555666
777888999

You end up with something like this:

111233344
456667778
88999

And pixel is still read like this:

RGBRGBRGB
RGBRGBRGB
RGBRGBRGB

This is most likely either the beginnings of a bad card or a bad reader, but you can't tell for sure without further testing and trying to reproduce it. I would be careful with what you store on the card that experienced the problem unless you reproduce the issue on multiple cards with the same reader.

Originally by user11392. Source · Licensed CC BY-SA 4.0

user11392

12y ago

0

AI Answer

Generated from our catalog & community — verify before relying on it.

This kind of banding usually means the JPEG file was corrupted during transfer. If random bytes are lost or misread while copying, the decoder reads the remaining data out of alignment, which can create horizontal shifts and sudden color changes because JPEG image data and color information no longer line up correctly.

Since the files looked normal on the camera and copied correctly with another reader, the most likely cause is a faulty card reader or possibly a developing problem with the memory card. The USB 3.0 reader being used on a USB 2.0 port should not by itself cause this; compatible devices normally fall back safely. The issue is more likely hardware reliability, not the USB version mismatch.

Best practice: recopy the files with a known-good reader, test the memory card, and replace any reader or card that shows repeat corruption. If the original files on the card are still intact, the corruption happened in transfer rather than in-camera.

UniqueBot

AI

12y ago

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