Canon Line Offset Noise

Started Oct 20, 2009 | Discussions thread
JimH Forum Pro • Posts: 12,911
Re: About options

GaborSch wrote:

JimH wrote:

What if the camera had more masked pixels to work from so that this could be done on a frame-by-frame basis?

I don't think it is worth of much thinking about a non-existent sensor.

I understand what you mean, but a large portion of this thread has been directed towards what we wish Canon would do. So it may have value to think about this in terms of what we'd request Canon to do in future models if we had any input.

Maybe they read these forums, maybe they don't. But my opinion is that if they'd give us a good batch of masked pixels along the bottom as well as along one side, then we could easily write software to put those masked pixels to use even if nothing was done with them in the camera.

Many manufacturers take suggestions from their users seriously. So we can still hope, I guess.

Or what about using the masked pixels that already exist?

The 7D has the useful masked area at the left side. This means, that the corrections can be differentiated row-wise (or use the global average), but we need column-wise distinction.

Right. We don't have what we'd really like to have ... in this model.

There is a nonactive area at the top too, but it is useless for this purpose. That was the first I experienced with when seeing the banding; the result is worse than the banding.

It makes one wonder what, if anything, they're doing with that area. It almost does seem as though things have been purposely made worse over the image portion of the frame when you compare it with the area on the left edge.

Look at the masked areas (contrast enhanced):

Funny is, that the left masked area does not show the banding, which is present in the image area; following is from a black frame:

It is very odd, indeed. Suspicious, actually.

I cannot think of a reasonable explanation for why we'd see this. I do see where John's thoughts of purposeful sabotage come from. (Don't flame me, Canon shills!) (Just kidding - sort of).

I think John's test showed that a correction factor, determined from just the bottom 100 rows, was sufficient to largely "fix" the problems all the way up to the top of the frame

John used the bottom of a black frame . That works well within the same image , i.e. the banding in the black frame can be removed that way (it is demonstrable by Rawnalyze).

I understand that entirely. That, again, was my point. His test using a black frame is a "proof of concept" kind of thing. Obviously, we don't really care about what we can do with black frames. We need masked pixels so that we can apply this to real frames.

However, we do not have that good strip of masked pixels.

But if we did , then it seems to me that a lot could be done. So it seems like a reasonable thing to request from Canon in future models. But then John has been doing that for years on here, so...

The idea even comes up about masking them off ourselves somehow. But you'd need to remove the entire "stack" over the sensor, and then you'd need a steady hand with the black paint to pull it off, too. Maybe some black electrical tape would do the job

Obviously, I'm kidding. But I'll bet that some place like the ones who remove the IR filters might be able to handle this. Just think of it. For $500, you could have your camera modified to have sufficient masked pixels to allow removal of most "banding".

Or... Canon could do this for us when they manufacture the sensors. I, like John and others, wonder why they haven't done this.

I'll bet there are a bunch of Canon engineers reading these threads and biting their tongues, unable to post for various reasons. Maybe there's a simple explanation. A flaw in our thinking that would make this unworkable. But I really don't see what it would be.

I tend to think that if we did have a masked area at the top or bottom that we could make use of, then some worthwhile improvements could be made in our image quality.

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Jim H.

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