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Scanners wanting huge files

  1. Sep 30, 2005 #1

    Pengwuino

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    So i got a new scanner right... and it can do up to 19200dpi... but i try to scan just to test it out and the software says it's going to create a 24 GB file with 24 bit color at that resolution. What the hell!?!??!

    What kind of resolution should I use and what file (jpg or bmp... ok well obviously jpg) should I use if i wanted to copy a real 4x6 picture and not notice any quality degradation.
     
    Last edited: Sep 30, 2005
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  3. Sep 30, 2005 #2

    russ_watters

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    19200dpi?!! What scanner is that?

    Copying a 4x6 photo, I'd probably use 300-600dpi. But try it and find out: If you zoom in and can see the grain of the photo, but not the pixellation of the digital image, you've used a high enough resolution. For scanning negatives you'd obviously need to go higher - perhaps 1200. But I couldn't imagine a need to scan something at 19200dpi.
     
  4. Sep 30, 2005 #3

    Pengwuino

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    HP Scanjet 4370

    I don't even really understand what dpi is :(
     
  5. Sep 30, 2005 #4
    dpi=dots per inch

    consider the 4"x6" photo russ mentioned.

    At 19200 dpi, 4"x6" = 76 800 x 115 200 dots (pixels) = ~8.8E9 pixels. 24 bit colour = 3 bytes/pixels, this comes out to about 26 GB to store the raw data for the image.

    But, Amazon.com says the scanner does 3600x7200 dpi, quite a bit less than the 19 200 you mentioned. If the scanner driver does go to 19 200, it's probably software interpolated.
     
  6. Sep 30, 2005 #5
    Pixels Per Inch is PPI, this is the density of images in digital medium, or in your computer.

    DPI is Dots Per Inch, and this is a printing term. So, for instance if you had a really huge image with a lot of detail, and you were printing on a very smooth paper, you would want at least 1440 DPI, most likely 2880 DPI, or more for advanced photographers.

    An image from digital to print, for great detail should have 300 PPI. Images start at 72 in the computer because that is how we look at them on screen, and that is the size they have to be to be on the web, or less. You start with a number of pixels and if you constrain the aspect ratios in images, then the image gets smaller when the pixels per inch are increased. Photo imaging programs have components that chop up the pixels and make them smaller, halving, quartering, etc. That is how you can have the same sized image in inches, but have more pixels for a smoother look.

    I have images that are greater than 500 megs, and that is not at all uncommon for photographers. Newer digital cameras shoot at 16 megs, or even more if you have the computer to handle that much, which would need about 2 gigs of ram, if not 4.

    One of the tricks of all this, is to make sure your monitor is set to the highest pixel density you are going to use in your images, so that when you repair things, you see them as they will be when you print, at least in content. Color calibration is another thing. But if you set your monitor, and your printer to the same icc profile then things should be more like what you see on the screen when you print. If your monitor is only set to 800x600 you fix a photo, and print it, and there can be large messy areas, in what you thought were blacks, but really they were dark areas with a lot of detail. I have made every mistake possible, in the learning of these few basics.

    By the way, an inexperienced printer will try to equate PPI and DPI and there is no real connection there. Your prints can be 720 dpi if you are using a very soft paper, like rag or watercolor, and sometimes that is better. But for smooth photographic images, tell the printer you want at least 1440 dpi. Other wise you will have droplet patterns in larger images.
     
    Last edited: Sep 30, 2005
  7. Sep 30, 2005 #6

    Pengwuino

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    Yah it must be software based. It says the 3600x7200 on the scanner too but it still had the option in hte software.

    I wasn't sure what DPI meant because i did that same calculation and got the gigabyte scale storage necessity and thought that I had the calculation wrong or didn't know what DPI meant.
     
  8. Sep 30, 2005 #7
    if you are doing pictures for things that will end up on billboards, you need that resolution to scale it up that size.
     
  9. Sep 30, 2005 #8

    Pengwuino

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    Man... scanning is annoying :P

    Seems like the only way to get a straight scan is putting the papers up to the border... but then for borderless photos, a bit is cut off during the scan. How can i do this better :P
     
  10. Sep 30, 2005 #9

    robphy

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    How much gets cut off? Most scanners have a preferred corner, which you should use.

    By the way, is your scanning software attempting to do any auto-cropping?
     
  11. Sep 30, 2005 #10

    Pengwuino

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    Well if you "preview" the scan during the process, it won't autocrop. The problem is with bordless 4x6's. Even with manual cropping, it doesnt get every last bit (its not really noticable... maybe 1/2mm-1mm. I assume the "preferred" corner is the top right here because theres a little diagram molded on that has an image of your paper on the top right hand side of the glass.
     
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