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Thread: Epson v800 8x10 transparency vertical banding

  1. #11

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    Re: Epson v800 8x10 transparency vertical banding

    For the old V800 scanner, using the eyedropper with a 5x5 average box on the unadjusted scan, I see about 9% difference between the light and dark areas. As you can see, it is really obvious in unadjusted photos. You can't have your sky looking like this:

    Click image for larger version. 

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    For the new V850 scanner, it is a lot better. I see 4% difference between light and dark areas when looking at the unadjusted original, which is tolerable as long as I don't use dehaze or clarity:

    Click image for larger version. 

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    By scanning the maximum available area of the 8x10 with the higher-res camera that crops the edges out, the variance drops to 2%, which is nearly undetectable. This explains why I never noticed before: within the area of a 4x5 negative, the variance is just 1% and likely below that when you just look at the sky area of a photo.

    Click image for larger version. 

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    The thing is that I do often boost the clouds with "dehaze" and sharpen with "clarity." I assume that's pretty normal in a hybrid film-digital workflow? Maybe people are doing DSLR scans for 8x10? I also can't quite fit the film borders in the scan area and I see a lot of film borders in other people's 8x10 scans. Maybe those are scans of contact prints?

  2. #12

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    Re: Epson v800 8x10 transparency vertical banding

    Quote Originally Posted by sabeluc View Post
    For the old V800 scanner, using the eyedropper with a 5x5 average box on the unadjusted scan, I see about 9% difference between the light and dark areas. As you can see, it is really obvious in unadjusted photos. You can't have your sky looking like this:

    Attachment 222924

    For the new V850 scanner, it is a lot better. I see 4% difference between light and dark areas when looking at the unadjusted original, which is tolerable as long as I don't use dehaze or clarity:

    Click image for larger version. 

Name:	img20220102_20541534.jpg 
Views:	13 
Size:	7.8 KB 
ID:	222925

    By scanning the maximum available area of the 8x10 with the higher-res camera that crops the edges out, the variance drops to 2%, which is nearly undetectable. This explains why I never noticed before: within the area of a 4x5 negative, the variance is just 1% and likely below that when you just look at the sky area of a photo.

    Click image for larger version. 

Name:	img20220102_17564882.jpg 
Views:	9 
Size:	6.8 KB 
ID:	222926

    The thing is that I do often boost the clouds with "dehaze" and sharpen with "clarity." I assume that's pretty normal in a hybrid film-digital workflow? Maybe people are doing DSLR scans for 8x10? I also can't quite fit the film borders in the scan area and I see a lot of film borders in other people's 8x10 scans. Maybe those are scans of contact prints?
    I have to confess I never use the dehaze or the clarity. I feel they create halos and other artifacts that look unnatural to me. I mostly use curve adjustment and gradients and other minor adjustments such as contrast, etc. and local doge and burn. But I’m not saying you shouldn’t use them, only that I don’t.

    I don’t have a fixed, unexposed 8x10 sheet to try it out on my v850 though, but I’ve never noticed something like this, perhaps I don’t do large enough adjustments to trigger them.

    I mostly scan my 8x10’s with the “lower res” optics (just a ~15% loss), right on the scanner glass (with an ANR glass on top) using the area guide. You can definitely scan a bit more than the 8x10 sheet so you can get the holder’s cut-outs if you center the sheet precisely.

  3. #13

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    Re: Epson v800 8x10 transparency vertical banding

    So I just took a new 8x10 x ray sheet and scanned it. Did it without fixing it but the emulsion is a “flat” middle grey (well, purple-ish but in b&w a nice mid gray), so it shouldn’t make a difference wrt assessing the banding issue.

    I scanned it with Epson Scan making sure all adjustments were off, at 1200 dpi in 16 bit greyscale, as tiff.

    There is vertical banding but it’s very small, the K values go from 47 to 50, or effectively a +/-1.5 %. It’s almost invisible on my screen, and with any information overlaid it wouldn’t show unless you’re just shooting against a perfectly white background (or grossly over-blown skies).

  4. #14

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    Re: Epson v800 8x10 transparency vertical banding

    I also took the image and applied a 30 clarity and a 30 dehaze in camera raw filter in PS. It shifted the overall level but the banding remained quite the same, a +/-2 % from 56 to 60.

    Of course these filters are probably non linear so one can’t make generalized statements, but it’s probably likely that with moderate clarity and dehaze adjustments it won’t also exaggerate the effect.

  5. #15

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    Re: Epson v800 8x10 transparency vertical banding

    Thanks Kiwi!

    I had assumed that the x-ray film was more opaque than it is with the purple emulsion.

    The 3% total variation of K with your scanner is 25% better than V850 I tested (4%). I'm surprised you didn't see the banding as more pronounced at +30 dehaze. I've been looking at +50 dehaze with no clarity adjustment, which is admittedly more than I would apply to a real photo. I imagine the V800 had real problems (9%) while the new V850s are just like this. 3% or 4% falls below the threshold that most people notice or care about.

    I'll have to test some real photos with sky to see if I care.

  6. #16
    Gary Beasley's Avatar
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    Re: Epson v800 8x10 transparency vertical banding

    I know astrophotographers do a darkframe shot used to subtract uneven pixel values from the images they shoot. Is this something that can be done with a scanner as well?

  7. #17

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    Re: Epson v800 8x10 transparency vertical banding

    Quote Originally Posted by Gary Beasley View Post
    I know astrophotographers do a darkframe shot used to subtract uneven pixel values from the images they shoot. Is this something that can be done with a scanner as well?
    In theory.. scan a piece of clear film than scan the actual film. It could work..

  8. #18

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    Epson v800 8x10 transparency vertical banding

    Quote Originally Posted by Gary Beasley View Post
    I know astrophotographers do a darkframe shot used to subtract uneven pixel values from the images they shoot. Is this something that can be done with a scanner as well?
    You would need to never change the selection of the scan area, not by one pixel, or it would not cancel it by subtraction. It’s different from a background picture which always covers the entire sensor.

    Or would would have to do a background scan prior to every single scan— gets a bit tedious (and you need to keep dust away from your reference background sheet…).

    Also, we would need to make sure it’s perfectly repeatable between (even consecutive) scans. Small fluctuations in the mechanical alignment could shift the banding response.

  9. #19
    Gary Beasley's Avatar
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    Re: Epson v800 8x10 transparency vertical banding

    This sounds like a feature that someone should build into the scanner driver, kind of like the IR scan to remove dust on many machines.

  10. #20

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    Re: Epson v800 8x10 transparency vertical banding

    I suspect it is a feature of the scanner -- specifically what it's doing with its calibration area. I just think it isn't very good at it over large areas. I'm sure it's a hard problem.

    If you look at the light source in the transparency unit, you can see it's a double row of discrete LEDs. Since the light source is extremely uneven, the scanner must be doing some magic to adjust for the dark and light areas. Furthermore, LED intensity will change over time, so the scanner must be periodically adjusting. I bet this was less of an issue with the older scanners that used a tube for a light source.

    One bit of corroborating evidence is that a speck of dust in the calibration area this will result in a white vertical line down the scan (if you are scanning a positive transparency). I imagine this to be akin to the scanner detecting a dimmer LED in that area and boosting the values illuminated by it as it travels down the length of the scan area.

    There is some instruction on removing scanner artifact banding in photoshop on the web. I tried it but it does not work satisfactorily and it is really a hack to cover up bad hardware. It works by scanning a clear (but tinted) transparency and then scanning a negative without adjusting the scanning area. As above, the clear transparency will show the scanner's bias as dark and light bands. You can place the bias scan over the negative as a layer in photoshop. It will be aligned as long as you don't change the scanning area. Rather than subtracting it, it works better to invert it and use it as a semi-transparent layer with one of the various layering methods (e.g. multiply). Sounds great but it doesn't work very well. I didn't work on it very long but I could imagine heavily blurring the bias scan first and using it as a mask for an exposure adjustment layer might work better.

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