Author Topic: [INVALID] "Bleeding" Dual ISO between lines on Canon EOS 550D [misunderstood]  (Read 2051 times)

sinuspi

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I'm getting odd "bleeding" from the bright stripes onto the dark stripes, as seen here:


Is this a problem only with older Canons like mine? And is there anything automated I can do about it? I mean, it's sure to wreak havoc on pictures after merging the exposures...

(This is an enlarged screenshot of a 100% zoom in Lightroom after converting the image from .CR2 to .DNG, if that matters.)

Walter Schulz

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Re: "Bleeding" Dual ISO between lines on Canon EOS 550D
« Reply #1 on: January 20, 2016, 01:33:14 PM »
LR process version 2013 may mess up here. Switch to older one and try to reproduce issue. If it is still bleeding give RAWtherapee a try.
Can you link an unaltered file out-of-the-cam showing this problem?

dmilligan

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Re: "Bleeding" Dual ISO between lines on Canon EOS 550D
« Reply #2 on: January 20, 2016, 02:08:27 PM »
Your problem is that you are demosaicing the unprocessed raw image. Of course there's going to be "bleed", that's what demosaicing does. The technical term is "interpolation". Since you only have one color for each pixel in a raw bayer image, the nearby pixels are used to interpolate the missing colors. You must keep in mind that when you "view" a raw image, you are not really seeing anything like what the data that is actually there. It is already highly processed just for you to be able to see it.

You have to run your image through cr2hdr first, before you jump to conclusions or make and faulty assumptions.

sinuspi

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Re: "Bleeding" Dual ISO between lines on Canon EOS 550D
« Reply #3 on: January 20, 2016, 02:23:55 PM »
@dmilligan: As mentioned, this is a screenshot from Lightroom, I'd assume it had already done all the interpolation a raw file needs...

@Walter Schulz: Raw Therapee is worse yet:


The raw file is here.

Walter Schulz

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Re: "Bleeding" Dual ISO between lines on Canon EOS 550D
« Reply #4 on: January 20, 2016, 02:28:01 PM »
LR doesn't know what Dual-ISO is and has no method to handle it. It has to be converted. There is a LR export plug-in doing the job.
http://www.magiclantern.fm/forum/index.php?topic=11056.0
Please do read Dual-ISO thread, too. http://www.magiclantern.fm/forum/?topic=7139.0

sinuspi

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Re: "Bleeding" Dual ISO between lines on Canon EOS 550D
« Reply #5 on: January 20, 2016, 02:33:23 PM »
Hmm. I (mistakenly?) assumed a Dual ISO raw file would simply have 2 lines of brighter ISO and 2 lines of darker ISO. However, indeed taking bayer pattern interpolation into account, these might absolutely not amount to two lines of PIXELS being brighter and darker, since it's sensors playing hopscotch, not pixels in a resulting image.

Thanks for the explanation. The plugin indeed does seem to do the job of loading it, although I somehow expected it to split my image into two lower-resolution images for me to merge using Enfuse. Can this still be done, however?

dmilligan

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Well, can be done, but you definitely don't want to. The results will be much much worse. cr2hdr does a lot to persevere resolution in the midtones (where the two ISO overlap) and prevent aliasing. If you split the two and then merge them manually, you'll get half resolution everywhere and really bad aliasing. cr2hdr will only have half resolution and some aliasing in the highlights and shadows where the two exposures don't overlap.