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Can someone explain why a 72dpi that went to print looked Great?

Apr 3, 2013 11:31 AM

Tags: #72dpi

Not sure if I should post this in the Photoshop or InDesign forum.

 

I am working on laying out a book in InDesign that will be printed at one of those self publishing companies. I've done a bunch in the past. So my friend that I do a lot of work with did a book on his own that has a grayscale photo of a B-24 bomber on the cover. The image was 72dpi and the dimensions of the image were 52.389" X 35.722". In InDesign the image was scaled down to about 7 inches wide. The book came back and the cover photo looked great. What is puzzling to me is why the cover photo did not look all pixelated because it was 72dpi. Is there something about the image that it was so large in it's dimension, and then it was scaled down? Can someone explain this somehow?

 

Just a note: Self publishing companies I beleave don't print their books on an offset printing press. I think they use highend laser printers. But I could be wrong.

 

Thanks,

 

Russ

 
Replies
  • Currently Being Moderated
    Apr 3, 2013 11:47 AM   in reply to iRuss

    iRuss wrote:

    The image was 72dpi and the dimensions of the image were 52.389" X 35.722". In InDesign the image was scaled down to about 7 inches wide.

    At which point the the effective resolution became something on the order of  538.56 ppi (52.389/7 x 72). When you scale the effective resolution of an image changes in reverse proportion to the scaling factor. This is exactly the same thing as changin the image width to 7 inches in Photoshop without resampling. No pixels change, you just change the size that you choose to print them.

     
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    Apr 3, 2013 11:49 AM   in reply to iRuss

    Scaling the image down from 35" wide at 72 ppi to 7" wide changes its Effective Resolution to approximately 360 ppi. If you selected the image in InDesign and viewed it's Actual Resolution and Effective Resolution, you would see this. (Peter posted almost at the same time as me. He calculated from the Height, I from the Width. The principle is the same.)

     
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    Apr 3, 2013 11:51 AM   in reply to Steve Werner

    I guess you think the image is portait, and I think it's landscape.

     
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    Apr 3, 2013 11:56 AM   in reply to Peter Spier

    Yeah, I guessed tall since most books are. You guessed wide, maybe imagining an image of that B-24 bomber would be horizontal.

     
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    Apr 3, 2013 12:01 PM   in reply to Steve Werner

    well aside from the subject matter, Adobe products (unlike painters, I've discovered after doing some museum catalogs) list the width dimension first.

     
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    Apr 3, 2013 12:22 PM   in reply to iRuss

    Bottom line. If you have a 72dpi image with a 4" x 5" dimensions, and you print it at the same dimensions, you're screwed! I know this but my friend does not. He will think you can get away with using 72dpi image regardless of what size you print them at… LOL! I feel a teaching moment coming on…

     

    I had that very same moment this last weekend, followed immediately by a "Kids these days..." moment. He literally could not see the pixellation. I got out the magnifying glass, and the face of the teenager in question acquired its mind-blown expression.

     

    Now I'm getting multiple low-res-camera-phone pics each day, with some comment like

    "it's everywhere, bro! how did i not see this before"

     
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    Apr 3, 2013 1:43 PM   in reply to iRuss

    in photoshop it depends on resolution in document size, but InDesign can Recalculate all pixel (pixel dimensons) related to the new size

     
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