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Thread: Selecting Scanner File Size for Printer Resolution?

  1. #1

    Selecting Scanner File Size for Printer Resolution?

    Hello! I've read "Real World Scanning and Halftones" and I have a question.

    I scanned a 4x5 negative and I wanted to print it 8x10 on my R220 with MIS inks. The scene contained a lot of fine line detail from limb branches. I set the white/dark points and the midtones, but no sharpening or curves. Scanning at 600 spi and then printing the image showed the limbs as irregular linear blotches.

    When I scanned at 2400 spi and then printed without downsizing, the interrupted blotchiness of the limbs disappeared on the 8x10.

    1) It appeared that there was an advantage to scanning at a higher resolution than the print size required for a 2x enlargment in order to capture the fine linear detail. Could this have been due to some sharpening in the software that I wasn't aware of?

    2) What is the advantage of downsizing a file when printing? I imagine the printer driver does the interpolation down to the appropriate ppi of the printer for the size of the print. Is there an advantage of doing this in the phot editing software as opposed to letting the printer do this? Best regards.

    Mike

  2. #2

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    Re: Selecting Scanner File Size for Printer Resolution?

    when you say you scanned at 600 spi what do you think that means?

    Your scanner has a fixed hardware number of sensors per inch which cannot be changed by software. Therefore the software either has to tell the scanner to throw away scan lines from perhaps alternate sensors(depending on specified spi) or it scans at the scanners native resolution and then downsizes before passing the output to you or perhaps it does both. Which it does I cannot say and I have seen absolutely zero information on this in any scanner reviews that I have ever read.

    So if you scan at 600 spi and your scanner has a native 4800 dpi then the question is; does your scanner software do a better job of interpolating/downsizing than you can do with your image editing software? It would seem from your results that your scanner software is not doing a good job at 600 spi and you would most likely benefit from scanning at the scanners native resolution and dowsizing in PS if that is what you are using.

    This raises the question for me of how it is that so many seem to find they get optimum results whilst scanning at lower than the scanners native resolution, since if the scan software is throwing away scan lines, then it is throwing away detail and if the scan software is interpolating/downsizing, then, as we all know, you also throw away detail and soften the result. Perhaps one of the scanner experts would like to explain how it can be that optimum results will be obtained by scanning at lower than the scanners native resolution. I would have thought that simple logic should tell you that a scan at native resolution and then print at a dpi which gives the required print size without downsizing would produce the optimum output.

    (n.b. by interpolation I mean resizing within the bounds of the original scan pixel dimensions. Upsizing would be extrapolation where the resize is outside of the bounds of the original scan pixel dimensions.)

  3. #3

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    Re: Selecting Scanner File Size for Printer Resolution?

    Quote Originally Posted by Michael Heald View Post
    Hello! I've read "Real World Scanning and Halftones" and I have a question.

    I scanned a 4x5 negative and I wanted to print it 8x10 on my R220 with MIS inks. The scene contained a lot of fine line detail from limb branches. I set the white/dark points and the midtones, but no sharpening or curves. Scanning at 600 spi and then printing the image showed the limbs as irregular linear blotches.

    When I scanned at 2400 spi and then printed without downsizing, the interrupted blotchiness of the limbs disappeared on the 8x10.

    1) It appeared that there was an advantage to scanning at a higher resolution than the print size required for a 2x enlargement in order to capture the fine linear detail. Could this have been due to some sharpening in the software that I wasn't aware of?

    2) What is the advantage of downsizing a file when printing? I imagine the printer driver does the interpolation down to the appropriate ppi of the printer for the size of the print. Is there an advantage of doing this in the phot editing software as opposed to letting the printer do this? Best regards.

    Mike

    First, one advantage of downsizing is elimination of noise.

    In the above example, it is not surprising that you got better results scanning at 2400 dpi.

    In the first example, you scanned a 4X5 negative at 600 dpi but probably got no better than a real 450-500 dpi. Then you made a 2X enlargement of the negative, further reducing file resolution size to 225-250 dpi. Degradation of the image could have resulted from sharpening artifacts, but at 250 dpi you are already well below the capability of your printer. Most people agree that improvement is possible in printing up to about 360 dpi, which is the equivalent of about 7 lppm. At 450-500 dpi you are below the minimum threshold of 5 lppm.

    In the second example you scanned at 2400 dpi and probably got an effective 1800 dpi. You made a 2X enlargement but still got an effective 900 dpi at the printing size, which is more than twice as much as you actually needed to meet the maximum potential of the printer, which is about 360 dpi or 7 lppm.

    Bear in mind that the weakest link in any optical chain is the one that determines final quality. In the first case the weak link was the resolution of the scan, in the second case it was the 7 lppm limit of the printer.

    In all cases I am assuming that the viewer is interested in critical definition at viewing distance of ten inches.

    When scanning negatives for digital printing most of the same considerations which apply to regular darkroom printing apply, except for the fact that photographic papers are capable of much higher resolution in dpi than what you get with an inkjet printer. Very expensive laser and LED printers are capable of much sharper results, but at great cost.

    In the July/August and September/October issues of View Camera there are articles by Robert B Hallock on how to optimize the sharpness of photographic prints. It is very well done and quite informative and I would recommend it to anyone interested in learning more about this issue. Another excellent source is a book by John B. Williams, entitled Image Clarity: High Resolution Photography. It was published before digital photography became common but is still a good reference on the subject of maximizing the sharpness of photographs.

    Sandy King
    Last edited by sanking; 9-Oct-2006 at 07:54.

  4. #4
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    Re: Selecting Scanner File Size for Printer Resolution?

    Hooooray Sandy, I highly recommend Image Clarity to everyone interested in fine printing and the pursuit of the best image. There is no other book, IMO, that covers the subject as well or as completely.

    Micahel, I find that scanning at the maximul real world resolution of your scanner produces the best results for a "master" file that you can then manipulate as needed depending on the final image. In terms of all of the consumer scanners this will mean setting your scanner to sample at ~ 2400 spi (depending on the settings). Later, in your editing software you downsize the image while retaining all the file info (e.g. you keep all the pixels but make them smaller).

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    Re: Selecting Scanner File Size for Printer Resolution?

    Quote Originally Posted by Ted Harris View Post
    Hooooray Sandy, I highly recommend Image Clarity to everyone interested in fine printing and the pursuit of the best image. There is no other book, IMO, that covers the subject as well or as completely.

    Micahel, I find that scanning at the maximul real world resolution of your scanner produces the best results for a "master" file that you can then manipulate as needed depending on the final image. In terms of all of the consumer scanners this will mean setting your scanner to sample at ~ 2400 spi (depending on the settings).
    That's what I thought. But in a thread here about a week to two weeks ago someone who sounded knowledgeable claimed that you should scan at the maximum stated ppi (e.g. 4800 ppi in the case of the Epson 4990) even though the maximum optical resolution for that scanner is about 2100 ppi.
    Brian Ellis
    Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
    a mile away and you'll have their shoes.

  6. #6

    Re: Selecting Scanner File Size for Printer Resolution?

    Hello! Thank you for the insights. I haven't seen the Image Clarity book. I'll see if I can track it down.
    I've been confused about what happens to an image when too much information is sent to the printer. For example, I've read that, if the printer can print up to 360 ppi resolution, then sending a file that has 600 ppi resolution wouldn't yield any better printed image. That is why several books/folks recommend scanning at the resolution determined by the final printer. By this recommendation, for example, it would seem that a 2x enlargement should be scanned at 400 to 720 ppi, depending upon the printer resolution (200 to 360 ppi).
    If I'm interpreting the comments in the thread correctly, folks are saying that it is beneficial to send files to the printer that are larger than the nominal resolution of the printer. For example, for a 360ppi printer, a 2x enlargement of a 4x5 negative should be scanned well over the over 720 spi. Such a file would give a better final image (presuming minimal manipulation) than if the image was scanned at 720 spi. Is this a correct understanding?
    What happens when I send a file to the printer without downsizing? For example, if the printer can handle 360 ppi and I send the scan of 2400 spi to the printer (far above what would be needed for an 8x10), does the printer driver resampple it for me? If so, is there image degradation compared to downsizing in an image editor? If there is no difference, why downsample at all and let the driver perform the task? Best regards.

    Mike

  7. #7
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    Re: Selecting Scanner File Size for Printer Resolution?

    The number 360 comes from the idea that Epson printers deal in multiples of that number: 720, 1440, 2880, etc. At the time when 360 was publicized, Canon printers were said to deal in multiples of 300.

    Since a few years is a long time in the world of technology, and printers have gone through several subsequent generations, it might be helpful to find out if these numbers are still relevent - but considering that Epson drivers still deal in multiples of 360, that number is most probably the one to use.

  8. #8

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    Re: Selecting Scanner File Size for Printer Resolution?

    PRINT TECHNOLOGY
    6 colour inkjet photo printer, Epson Micro Piezo™ print head
    Epson Variable-sized Droplet Technology with minimum 3pl droplets
    Print head of 540 nozzles (6 x 90 per Black, Cyan, Magenta, Yellow, Light Cyan, Light Magenta)
    PRINT QUALITY Up to 5760* x 1440dpi, *optimised dpi on suitable media using RPM (Resolution Performance Management)
    The above is from the spec for your printer. That means it will print upto 1440dpi
    note that the print nozzle line is 90 nozzles so mutiples of 90 is what it will most likely do best in terms of print resolutions. So 360 is good as is 720 or 1440.

    You don't say what scanner you have but I'll assume an epson 4990 which has a native resolution of 4800. I'll also assume you are going to print at 720dpi and that the actual print area is going to be exactly 10x8 inches. So you will need an image of 7200x5760 pixels. If you scan at 2400ppi then you you will get an image of 12200x9600. The scan software will probably have done some downsampling to get those numbers and it was probably bicubic sharper but maybe not. Instead I would scan at 4800ppi which gives you an image of approx 24000x19200 pixels. Apply some very light unsharp mask to that image. Say 0.7 pixel radius by 50%. Then dowsize to a multiple of the final image dimensions. So that would be to 14400x11520. Use bicubic to do it. Then apply the same light unsharp mask (0.7 50%) and then dowsize using bicubic to 7200x5760. Then set the document dpi to 720 by first unchecking the resample check box and then set the dpi to 720 and press OK.

    now you can print at 720dpi.

    note that the final dowsize is by a factor of 2 which gives good results. You may or may not apply final sharpening before print but not much should be required if any.

    let us know how it goes.

    (note that if you were to scan at 2400dpi you would need to downsize from 12200x9600 to 7200x5760 and since that is not a factor of 2 then the final image would likely need more sharpening than doing it the other way)

    Also you could downsize by a factor of 2 again and set document dpi to 360 to print, in which case scanning at 2400 may be quicker but you don't know how the scan software is doing its image sizing. Silverfast seems to do it pretty well. Your scan software may not, so doing it in PS after scanning at scanner hardware resolution is a good option if you are uncertain about your scan softwares capabilities.
    Last edited by robc; 9-Oct-2006 at 20:51.

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