Exporting to JPEG, 300dpi for a online book publisher

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5 comments

  • Avatar
    Bernhard Martin

    No, the quality slider does the setting of more or less compression.
    This has nothing to do with the dpi.

  • Avatar
    Mike Miles

    Dave, I asked this question also. It appears that Luminars save or export is only rudimentary compared to other software. For instance, you can't lock the DPI with a pixel dimension....say 100 @ 800x600 for screen usage, according to Skylum. That would be resizing anyway.

    First, set the slider to maximum quality. Then the rest is math. Instead, use this calculator where you just input the dimensions. Read the theory or scroll down to "Photo Size"

    https://planetcalc.com/1688/

     

    Also read this other post I made.

    https://community.skylum.com/hc/en-us/community/posts/360032811112-Resize-Change-both-width-and-hieght-keep-ppi-and-adjust-capture-for-a-8x10-print

     

  • Avatar
    Richard Huggins

    You can specify dpi in tiff. So export as a tiff then convert to jpeg outside Luminar. I had seen Skylum was going to fix this "in a future release" like they promise with everything.

  • Avatar
    Mike Miles

    I've made this simpler, since my previous deleted post was partially  wrong.

    Sizing for Print

    For example, if you want to print an image 4 x 6 inches at 300 ppi, then you need a file that has at least 4 x 300 (1200) pixels along its short side and 6 x 300 (1800) pixels on the long side. So, it needs to be at least 1200 x 1800 pixels in size.

    To print an 8 x 10 inches at 300 ppi use the same math – multiply the printed image width and height in inches each by 300 pixels. The result is 2,400 x 3,000 pixels, which is the size image you need to print an 8 x 10 at 300 ppi.

    Examples for 300 dpi/ppi

    3 x 5 = 900 x 1500
    4 x 6 = 1200 x 1800
    5 x 7 = 1500 x 2100
    8 x 8 = 2400 x 2400
    8 x 10 = 2400 x 3000
    8.5 x 11 = 2550 x 3300
    9 x 16 = 2700 x 4800
    11 x 14 = 3300 x 4200
    11 x 16 = 3300 x 4800

    If you still need a chart of values, most printing  services have them online. 

    Example:

    https://www.nationsphotolab.com/pixelchart.aspx

    So, what do you do if you don't have enough (native or beginning) resolution? Then you have to resize your image by entering the needed values.  The image software will resize, with some degrading  or loss in clarity, to achieve the new size.  Cropping works similar.  This is why you may want to sharpen after resizing.

     Sizing for Screen

    When it comes to displaying images on the screen you need far less pixels than you do for printing. This is because the density of pixels on the screen is far less than what is required for printing. So, for example if a typical monitor resolution is 1920 by 1080 pixels in size, to fill the monitor you only need an image that is 1920 by 1080 pixels in size. That’s about the same size image you need for a 4 x 6 print at 300 ppi, yet this size image displays perfectly on a 23 inch diagonal monitor.

  • Avatar
    Dave Biggs

    Thanks all , especially Mike for the list, great info.

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