Lines on images? - DPChallenge Forums

Canon EF 24-70mm f/2.8L USM

07/15/2007 08:40:21 AM · #1

I've noticed on a few images at 100% crop that there are vertical bars in the image. I don't know where they come from or whether it is a problem with the camera, or something I have to live with. Here's a sample...

They seem to show up most on skin, possibly more so when slightly underexposed. I don't know if this is some sort of sensor screen that's showing up? Maybe a peculiarity of the 400D?

It's not directly related to aperture. The sample was taken at f/5.6, and I have plenty of shots at f/5.6 where it doesn't show up. It's not a major problem, but I'm curious to know what it is, and whether it is common on this camera, and on others.

dwterry

Canon EOS-1D Mark III

07/15/2007 08:47:34 AM · #2

Raw/Jpeg? If shot with raw, which converter?

At 200% magnification, you're bound to see strange things like this... it may just be an artifact of the demosaic algorithm in camera or the bayer filter on the sensor. Or it might be how your raw converter interprets that same data.

Canon RF 24-70mm f/2.8 L IS

07/15/2007 08:53:04 AM · #3

Shot JPG. Doesn't look like normal jpg artifacts. I just checked, and the darker bands are roughly every 6 pixels. Strange that it only shows up on some images... I just checked, and when they are there, they are there on the whole image, not just the skin tones. That's just where I noticed them first, because that's where I tend to be looking.

Message edited by author 2007-07-15 08:55:48.

kirbic

Canon EOS R5

07/15/2007 09:32:05 AM · #4

Banding, as this is called, is not too uncommon. You're going to see it more at high ISO, and when "pushing" exposure up in post processing (including RAW conversion).
They usually run horizontally (the long direction) and are related to the fact that the sensor data is read out row by row.
If you're seeing them vertically (the short direction) that is unusual. If they are slightly angled, it is possible that the cause is high-frequency radio interference.

Canon RF 24-70mm f/2.8 L IS

07/15/2007 09:56:20 AM · #5

Thanks kirbic. At least I know my camera isn't broken. :) Actually, the lines are 'horizontal'. The shot I took it from was a portrait shot, so it was actually my camera that was vertical, not the lines. These shots were ISO 400. I wonder what influences this. Other shots ISO 400 don't have it. I wonder if camera/sensor temperature is related?

kirbic

Canon EOS R5

07/15/2007 10:09:23 AM · #6

Yes, sensor temperature has a visible influence. Shots taken in cold weather will be less noisy.
Whether banding is noticeable on a particular shot is also dependent on the content of the shot. Shots with darker tones tend to show the banding more, and shots taken in predominantly red light (like tungsten) often show it more, because the blue and green channels get boosted by the WB compensation.
In order to minimize the visibility of banding, Expose to the Right whenever possible. This will mean pushing exposure down in post-processing, with the result that any noise, including banding, is minimized.