keeping resolution when cropping

Discussion in 'Photography Beginners' Forum' started by onFire, Dec 14, 2011.

  1. onFire
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    onFire New Member

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    just curious if anyone can explain how to keep the GREAT resolution i have before i crop, after i've done so. i usually crop for a 4x6, but the pixel dimensions go down dramatically (thus, the picture looks more grainy when i zoom in). is 4x6 a good size to crop or should i be doing something else? i'm using photoshop 5.5. thanks for the help!
  2. Robin Usagani
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    Robin Usagani Well-Known Member

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  3. Big Mike
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    Big Mike I am Big, I am Mike Staff Member

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    Welcome to the forum.

    This is sort of like asking how to crop a printed photo, but keep the paper. :scratch:
    When you crop, you are cutting off part of the image...thus you are cutting out some of the pixels. The resolution in the rest of the image should remain the same (unless you have it set to change the resolution).

    I don't know about Photoshop 5.5 in particular (wow, that's an old version). But in modern Photoshop, the crop tool allows you to choose a size/ratio and a resolution. So if you want a 4x6 at 300 PPI, you just have to enter those numbers into the fields. If the photo has more or less resolution than that, it will automatically adjust the image...and you'll end up with a file that is 1200x1600 @ 300 PPI.

    So what size image are you starting with, and are you using the crop tool to set the new resolution or not? You don't have to, you can crop first, then use the Image>Size command to set the size/resolution.

    Also, how close are you cropping?
  4. KmH
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    KmH Helping photographers learn to fish

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    Cropping means discarding pixels. Discarding pixels lowers resolution. Don't crop to a size. Crop to an aspect ratio. Then define the size by assigning a value for the PPI.

    4000 pixels x 2666 pixels is a 4x6 if the assigned PPI is 666.66 pixels-per-inch.

    4000 pixels divided by 666.66 pixels-per-inch = 6 inches. 2666 pixels divided by 666.66 pixels-per-inch = 4 inches
    4000 pixels divided by 333.33 pixels-per-inch = 12 inches. 2666 pixels divided by 333.33 pixels-per-inch = 8 inches
    4000 pixels divided by 166.67 pixels-per-inch = 24 inches. 2666 pixels divided by 166.67 pixels-per-inch = 16 inches

    4x6, 6x9, 8x12, 10x15, 12x18, 16x24, 20x30, 24x36, etc, are all the 3:2 aspect ratio.

    Wallets (2.5x3.5), 5x7, 10x14, 20x28, etc, are all the 7:5 aspect ratio.

    4x5, 8x10, 16x20, etc, are all the 5:4 aspect ratio

    [​IMG]
  5. onFire
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    onFire New Member

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    @SchwettyLens: Thanks for the pixel tutorial :)

    @Big Mike: Sorry I didn't mention the CS in my PhotoshopCS5.1, so it's the newer version. My images start out at 9.44x14.187 @ 300 ppi (2832x4256). I usually use the crop tool to crop the image to a 4x6 since the aspect ratio of my camera is 3:2 and my resolution stays at 300 ppi. I'm not cropping it down too much, but when I zoom in @ 200% it obviously doesn't look as clean as I'd like it to. What I am worried about is when I go to enlarge these images onto something like a 16x20 canvas, will it look that bad?

    @KmH: Thanks for the aspect ration break down. When I upload the pictures into PS they automatically have a 300 ppi resolution. Should I be changing the ppi to a higher number once it's been uploaded or do I have to do that in the uploading process (or is 300ppi more than acceptable)?

    Also, in PS when I go to save the picture I have edited, it asks about JPEG image and baseline options... i've been saving my images at quality: 10 and baseline: standard; will these options change the way an image looks once it's printed? Thanks again.
  6. ph0enix
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    ph0enix TPF Supporters

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    At 200% it will never look as clean as you would like it to. It's not because it's losing quality due to cropping but because you're trying to go beyond 100% and it will never maintain the same quality at that ratio. You can't make 1 apple (100%) into two apples (200%) - similar analogy. I'm beginning to wonder if this post is for real.
  7. KmH
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    KmH Helping photographers learn to fish

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    Your camera is setting the 300 PPI, not Photoshop. It's a default PPI value. Change the PPI in Photoshop using Image > Image Size and in the Image Size dialog box set the PPI to determine size of the print you want.

    By the way. PPI only applies to a print. It does not apply to electronic display. For electronic display only the pixel dimensions have meaning.

    Your D3s delivers images by default with a native aspect ratio of 3:2 and pixel dimensions of 4,256 x 2,832 pixels, though you can change that from the 3:2 default to 5:4 or 1:2.
  8. vipgraphx
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    vipgraphx Well-Known Member

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    What I usually do is if you have PS go to Image/image size and select the size you need then make sure all boxes checked and from the drop down menu make sure you select best for reduction or if you are enlarging you would select best for enlarging.

    It has always worked for me. Not sure if I am doing it wrong or right.

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