How to increase dpi in photoshop

Discussion in 'Graphics Programs and Photo Gallery' started by karimmaalouf, May 17, 2012.

  1. karimmaalouf

    karimmaalouf New Member

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    Hello,

    i have a picture shot with a canon 1000D: resolution & size: 72 dpi , 3888x2592 pixels

    can i , in photoshop, increase the DPI of this picture to 300? and how do i do that...

    thanks
     
  2. Mach0

    Mach0 TPF Supporters

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    Yes. Image size. There's a section.
     
  3. karimmaalouf

    karimmaalouf New Member

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    hi Mach0, yes there is a section in image size, but when i change resolution to dpi my picture size changes from 3888x2592 to 16200x10800! is this normal? should i resize the image after changing the dpi in order not to lose quality? also, i have the check under "resample image: Bicubic (best for smooth gradients)" is this the right option?

    thanks again
     
  4. Big Mike

    Big Mike I am Big, I am Mike Staff Member

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    Firstly, DPI is a printer setting. Dots (of ink) per inch.

    What you are talking about it PPI (pixels per inch).

    In terms of quality, the PPI number is mostly meaningless. It just tells a computer how larger to display the image. You could have an image that is 3888x2592 at 72 PPI and it will be exactly the same quality as a file that is 3888x2592 at 600 PPI.

    The important part is how many pixels it has...3888x2592.

    The confusing part is that sometimes, when you go to print etc., the printer will take the size in inches (on screen at 100% zoom) as the print size. So in that case, you probably do want to change the PPI to something like 300.

    To do this, without changing the size of your image (in pixels), you go to the Image Size dialog, but before you change anything, un-check the 're-sample' box. This will allow you to change the PPI without it automatically changing the pixels.

    As far as which resample option to choose...that is for when you actually do change the number of pixels. If you add pixels (make the image larger) then you want bicubic smoother. If you make the image smaller, then you want bicubic sharper.
     
  5. Mach0

    Mach0 TPF Supporters

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    Somehow I read dpi and assumed the op meant ppi. ;)
     
  6. KmH

    KmH Helping photographers learn to fish

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    A very handy book for Photoshop user's to have on the shelf near their computer for reference is - Adobe Photoshop CS5 for Photographers: A professional image editor's guide to the creative use of Photoshop for the Macintosh and PC

    The numbers you saw "16200x10800!" are the result of the difference between 72 ppi and 300 ppi. If you do the math the difference between 16200 pixel, 3888 pixels, and 72 ppi, 300 ppi is 4.16666...

    A close look shows that Photoshop is careful to use the correct term - ppi, or pixels per inch. PPI is an input devices resolution, like digital cameras. DPI is an output device resolution, like an inkjet printer.

    The Image size dialog box normally opens with the Resample box checked. With Resample checked, when you alter one set of units all the others adjust at the same time.
    If Resample is not checked, the pixel dimensions will be grayed out and any changes you make will only not affect them.

    Resampeling to a higher resolution means new pixels have to be made up that were not actually recorded by the image sensor.

    Why do you want the ppi of the photo to be 300 ppi? PPI determines the physical size of a photo (a print).

    A photo that has pixel dimensions of 3888x2592 pixels that is assigned 300 ppi will print - 3888 pixels ÷ 300 ppi = 12.96 inches by 2592 pixels ÷ 300 ppi = 8.64 inches.

    Larger prints, like wall size prints get viewed from further away. If you want print larger than 12.96" x 8.64" you can use the above equation pixels ÷ ppi = print side length and a little algebra to calculate how many ppi you need to atain a specific print size pixels ÷ print side length = ppi

    If you want a 20" x 30" print - 3888 pixels ÷ 30" = 129.6 ppi and 2592 pixels ÷ 20" = 129.6 ppi

    129.56 ppi may be more than sufficient. It really depends on the photo. If I was wanting a 20x30 print of a persons face i would want at least 180 ppi.

    Again using the same equation and a little basic algebra we get the equation print side length x ppi = pixels or 30" x 180 ppi = 5400 pixels.

    For increasing the resolution the image has to be reinterpolated. Many Photoshop experets, Scott Kelby and Vincent Versace come immediately to mind, recommend using the Bicubic Sharper interpolation algorithm for increasing the resolution of a photo.
     
    Last edited: May 17, 2012
  7. BlueMeanieTSi

    BlueMeanieTSi New Member

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    You only want to increase the PPI to what the printer you are using needs as the minimum resolution. If your printer accepts 180-760 and your image is 72ppi, only increase it to 180.

    (This info is straight from the manufacturer.)
     
  8. karimmaalouf

    karimmaalouf New Member

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    hi to all of you.

    first i would like to thank you all for your feedback, but i have to say i am completely lost now.

    here is the thing: i entered a photo contest with the photo attached to this post.

    this photo has been selected among the 12 best pics, so now i have to send them high resolution pic. as of their specification (that you can find here: Rules & Regulations Photo Competition - The Garden Show & Spring Festival 2012 ) they want the high-res fomat: Jpeg, Png, Tiff, 3MB, 300 dpi

    if i open my picture in photoshop/image size, it tells me it's 72 dpi... $IMG_7755.jpg
     
  9. karimmaalouf

    karimmaalouf New Member

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    Hi Peano,

    " the deadline was April 27. Aren't you a bit late on this? " yes the dealing was april 27 to submit the image low res which i did, and now i am selected to the second round. they want me to send now the high res image matching their requirements.

    thanks for processing the image , but when i opened your second link (high res) in photoshop it shows still 72 pixels/inch...

    thanks again
     
    Last edited: May 17, 2012
  10. BlueMeanieTSi

    BlueMeanieTSi New Member

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    Imageshack probably reduces it. You'll have to zip or upload it somewhere else.
     
  11. BlueMeanieTSi

    BlueMeanieTSi New Member

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    I see, you gave the impression the file was already 300ppi.
     
  12. KmH

    KmH Helping photographers learn to fish

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    Many Canon camera's assign a default resolution of 72 ppi when the shutter is released.
     

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