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DPChallenge Forums >> Tips, Tricks, and Q&A >> Scan Line Removal?
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 05/10/2006 11:40:46 PM · #1
So, I hope this isn't a repeat question. I can't find anything in the forum archives - either with the forum search or google (site:dpchallenge.com). All I found is a vague reference in the comments for a challenge submission.

At any rate, it seems like most of the time when the ISO is set higher than about 200 on my Canon digital rebel, that I get anoying scan lines, as in the photo below.

Photo

For reference, the photo above was:
1) taken in raw mode
2) converted to JPG with rawshooter pro to tiff
3) converted from tiff to jpg with photoshop
4) and finally, the original EXIF data put back in with exifer

It doesn't seem to matter if I'm in manual mode, or one of the automatic modes on the camera. Nor does it seem to matter if it's in JPG or raw mode - I still get the same problem. Usually it worse the higher the ISO, and the lower the lighting conditions.

My understanding of how the camera works, is that the ISO setting turns up the preamp gain before the image is sampled by the ADC within the camera (or something similar). I don't quite understand why a higher gain would cause the bands that I'm seeing. Maybe something to do with the camera's other settings?

Any Ideas on how to remove them in photoshop or other tools?

Thanks in advance,
Russ

Message edited by alanfreed - Editing to link to big photo.
 05/10/2006 11:49:25 PM · #2
That is odd...

question: Does the RAW straight from the camera look like this?
 05/10/2006 11:50:09 PM · #3
I'm no pro, but I think your camera is defective. I would be contacting Canon about this.
 05/10/2006 11:58:01 PM · #4
Originally posted by BakerBug:
I'm no pro, but I think your camera is defective. I would be contacting Canon about this.


I agree. There are referred to as banding, right?
I think it's a sensor problem
 05/11/2006 12:03:03 AM · #5
Yea, the raw image looks like this too.

The wierd thing is that it works fine at low ISO (100-200) with very long (5 min.) exposures.

Russ
 05/11/2006 12:11:27 AM · #6
You might want to check your firmware to see if it is up to date.

Also, which software are you using for conversion? There was a problem with DPP (supplied by Canon) and some cameras and an update to that software may be in order as well.
 05/11/2006 12:13:50 AM · #7
Originally posted by russbbrink:
Yea, the raw image looks like this too.
The wierd thing is that it works fine at low ISO (100-200) with very long (5 min.) exposures.


It doesn't matter, I mean, if it happens at ISO 400, 800... Then it's a problem already. I mean, it's a 300D we're talking about here.
 05/11/2006 12:22:49 AM · #8
Canon website says 1.1.1 is the latest, which is what the camera says too.
 05/11/2006 12:27:56 AM · #9
Anyway,

I've already got quite a few photos I'd like to fix. Anyone got photoshop or other postprocessing ideas?

Thanks,
Russ
 05/11/2006 12:34:41 AM · #10
That's gonna be a hard fix... how good are you with the clone tool?
 05/11/2006 07:49:34 AM · #11
In RAW conversion, was the exposure pushed up a lot? That will make the appearance of the banding much worse. Still, if you're seeing this level of banding, you might want to talk to Canon.
 05/12/2006 12:36:37 AM · #12
I didn't do any exposure adjustments in the example photo
05/14/2006 01:10:18 AM · #13
Obviously, you need to get your camera fixed, but for your existing photos, this *might* work. I haven't tried this trick on banding/scanlines, but it may just do the trick.

Look at the EXIF information of the image you want to fix, make a note of the ISO, shutter speed and f-stop, and any other settings you can reproduce.

Using settings as close to the original image as possible (ambient temperature could factor in as well) take a PURE WHITE shot. Use a white card and lots of light.

In Photoshop, place the white image on top of the original image in a seperate layer. Change the blending mode of the white image layer to Diference or Exclusion (I'm not sure which will produce better results). You may also need to invert the white image.

I use a technique like this to reduce sensor noise on long exposures, you're doing the inverse, but it might work.

Let me know how it goes!
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