Scanning B&W negative (why scan in RGB ?)

Discussion in 'Black and White' started by sassan_hazeghi, Oct 2, 2005.

  1. For scanning B&W (traditional silver) negatives, some people seem to
    prefer/recommend using RGB, rather than gray scale mode.
    Assuming a well calibrated scanner and a truly neutral (gray)
    negative (no purple tint and correct profile for the film base+fog)
    shouldn't all the color channels record identical reading ? If the
    dynamic range of a given channel is above that of the other two, I
    can understand the possible advantage of scanning in RGB mode and
    using that channel as the gray value (in which case, the gray scale
    scanning mode should be able to do the same on its own (use the most
    sensitive channel, rather than averaging the 3 color channels ?)

    The file size of an RGB scan is so much larger than gray scale that
    I would like to scan my negatives in gray scale if there is no clear
    advantage to an RGB scan.

    Thanks for any light that others can shed on this topic,

    Sassan.
     
  2. If you scan a b&w negative in RGB and split the channels into separate red, green and blue, you'll immediately see the difference. Not only is overall tonality dramatically different, so are noise and grain.

    Scanning in RGB gives you more options to finesse the final output.

    For example, you can selectively use noise reduction or grain reduction techniques, as well as sharpening and other adjustments, on just one channel rather than all three.

    In other cases you may find that printing from just one channel produces the results you want.

    Even if you decide to reduce the final image to grayscale, you will still get some benefits from making adjustments on the RGB scan.
     
  3. jtk

    jtk

    I'm not convinced that RGB offers any advantage when you use Vuescan combined with printing "black only" with an Epson or using a proper B&W printer driver (as opposed to posting online or printing via minilab or printing directly from Photoshop). There seem to be only two proper printer drivers for B&W, and the only one that seems to make sense (according to people who report comparisons online) is QTR...quadtone.

    One has tremendous controls in Photoshop with greyscale scans, more control than one has in a wet darkroom. However if a person loves digital tweaking, scanning RGB offers even more control...the value of the additional control is subjective..."more" isn't necessarily "better."
     
  4. Greyscale offers up to 256 shades of grey per scanned pixel. 256 levels between pure black and pure white. RGB offers potentially 16.7 million variations of colour per pixel. Therefore, potentially, you can store more information of your scanned image using RGB scanning. By the way, I scan the finished photograph, not the negative.

    I think of my scanned photographs as digital negatives - for archiving my work to DVD. I want to store as much information about the scanned image as possible in my 'negative' and so always scan RGB. This captures every nuance of the picture inc. paper base colour... as well as the digital information of the greyscale of the image.

    As software improves so will the ability of the program to use this digital information. I recommend saving as much info about the picture as possible and therefore using RGB.

    John

    www.pictorialplanet.com
     
  5. This is a very good question. I use vuescan and Minolta film scanners. Vuescan seems very capable of producing a low noise, full scale grayscale scan. In fact, I have noticed more noise and grain in my RGB scans of B&W negs. This is not to say that every negative will be better in grayscale. It very much depends on the film type, and output resolution whether grayscale or RGB is better. However lately I find myself scanning grayscale and adding color via Photoshop's Duotone function.
    00DjwC-25900584.jpg
     
  6. I scan b&w as 16 bit grey scale. This gives many more than 256 levels, in fact it gives the same number as desaturated 48 bit RGB.

    Steve
     
  7. This is a good question, as we're ultimately talking about shades of gray. However many distinct shades of gray you theoretically create in scanning, a only small fraction will be distinguishable in a finished print. I've tried scanning the same images in grayscale and in RGB and have not seen a discernable difference in final output. I would note that I cannot apply PhotoKit Sharpener to a grayscale image. Then again, I cannot print using Quad Tone RIP unless an image is in grayscale. So, I've been scanning and editing B&W images in Nikon's "Adobe" RGB. Then, I've been converting images to grayscale for printing and web use. This seems to be working pretty good.
    00Dk0A-25901784.jpg
     
  8. Eric, I use the Photokit sharpener too. I scan in greyscale to save space and then convert to RGB before sharpening.
     
  9. You have to remember that when you scan in color, the image will be build in pixels at the
    rate of one third each chanel (RGB) So, if the final image is 9 MB then each chanel will take 3
    MB. When you convert from RGB to gray scale or b&w, you eliminate 2 of the 3 chanels
    (usually leaves the red one) and you finish with an image with 3MB. The best solution is to
    only desaturate the image, the result will be a file that has the 9 MB and still will be an RGB
    file, with lots of info on it.
    In silver-based negatives, the original image is also a color one.
     
  10. Steve, you're right. I've converted some images to grayscale before final PKS output sharpening, then switched back into RGB for output sharpening without incident.


    pericles, the question is whether all that excess data will ultimately be represented on a computer screen or in a print. Will your 9 desaturated MB of information produce an image that's sharper or richer in tones than a 3 MB grayscale image of the same scene? So far, I haven't seen any difference.


    And again, the endgame for me is prints. If I started with an RGB scan and finish with a print from a desaturated RGB print, I'm nowhere, as my Epson 2200 produces suck-ass B&W prints without a RIP. With Quad Tone RIP, I'm getting some swell prints, but I have to print in grayscale.
     
  11. I think it depends on your scanner and workflow. 90% of my scanning is from conventional B&W film, using a Minolta Scan Dual II 35mm film scanner with Vuescan. I used to scan in RGB mode, but then realized that there was basically no difference in grain or tonality between the individual channels in my scans, meaning that the extra "bit depth" was being wasted. I now scan all my B&W work as 16-bit grayscale, which generates 19-MB files. I do what I can in PS to the 16-bit file and then switch to 8-bit for finer manipulation.
     
  12. With vuescan the 16b grayscale option works the best for me. Not so large files and you got the data from the negative.<br>Scanning in RGB then desaturating only gives you a 3 times bigger file. The fact the file is 3 times larger has nothing to do with the amount of information it holds. The data are split over 3 channels instead of one, and in the end you just lose diskspace.<br>
    I think we all have your own workflow, but sometimes we should try by ourselves, compare the results of different suggestions and get rid of some myths once and for all.<br>
    I'll probably shock a couple of people here, but usually the next step in my workflow is to convert in Lab mode and only keep the lightness channel. This is something that suits me because I can get closer to the final look I want for my prints by easily getting rid of the greyish "cast" from my vuescanned negs. I would not recommend people to implement this in their own workflow unless they like the look, but greyscale scanning is a no-brainer for me.
     
  13. jtk

    jtk

    I think a lot of this has to do with the merit of the original image.

    If it's seen better as "a print," more than as photograph, then I'd accept that scanning an original print as part of work flow might be defensible, but as an eccentric approach with a certain character.

    If instead the image itself is strong there seems little credible argument for intruding a wet print into the otherwise superior digital workflow (if RGB digital's good enough for posterity, it's good enough for 2005).
     
  14. I scan my B&W as a grayscale, let the scanner software handle inversion after selecting the levels manually, and scan as 16 bit, then adjust levels again in PS5 LE before demoting to 8 bit for other editing and eventual storage. With my Agfa Arcus 1200, this works very well and produces better results than I've had when trying to scan as RGB.

    Different scanners and different software produce different results, though, and different negatives can make a big difference, too.
     
  15. I recently discovered that my venerable PhotoSmart 35 mm scanner was not resolving color slides well. The R, G and B images of a BW negative or positive are not coinciding. When I separate the color channels into 3 BW images, the resolution in any of the three is better than the resolution of the sum. Close examination of the original image shows that displacement of the three subimages is a greater cause of loss of resolution than difference in size. This displacement also cause a color shift, so that an original that looks neutral make a greenish scanned image, probably because the eye is most sensitive to the displaced green image.

    It may be possible to correct my scanner, but I have lost the original software. It may be the only one that has this defect, but it is something to be on the lookout for.
     

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