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photoshop cropping help!!

smllycatsmllycat Registered Users Posts: 17 Big grins
edited August 22, 2012 in Finishing School
I don't know what I did, but somehow when I crop my photos, the dpi is changing!! I've been doing this forever and this has never happened! When I click on crop, I am not changing the resolution - I don't know what's going on? I always leave it at the 72dpi, but now after I crop it's automatically changing the dpi to something lower!! Please help with any suggestions!

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    ziggy53ziggy53 Super Moderators Posts: 23,891 moderator
    edited August 12, 2012
    Generally, the Cropping Tool is used to crop the image to a particular aspect ratio. In this case, it's best to leave the Resolution box empty. If there is an entry in the resolution box, highlight whatever it is and then use the Delete key to clear the entry.
    ziggy53
    Moderator of the Cameras and Accessories forums
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    JBHotShotsJBHotShots Registered Users Posts: 391 Major grins
    edited August 20, 2012
    ziggy53 wrote: »
    Generally, the Cropping Tool is used to crop the image to a particular aspect ratio. In this case, it's best to leave the Resolution box empty. If there is an entry in the resolution box, highlight whatever it is and then use the Delete key to clear the entry.
    I'm not so sure that makes sense to me. Leaving it empty will always crop at the native resolution of the camera, which in most cases is 240dpi. I'm not a Photoshop pro but unless I've missed something why wouldn't you want to crop it at your output dpi?
    Jamie
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    PeanoPeano Registered Users Posts: 268 Major grins
    edited August 20, 2012
    I'm not a Photoshop pro but unless I've missed something why wouldn't you want to crop it at your output dpi?

    I think it's good practice to avoid resampling unless it's necessary for printing. Especially if resampling adds pixels, you'll lose some image quality.

    The OP specified 72 ppi, which obviously isn't for printing. If you're cropping for the web, resolution is irrelevant anyway. You can set it at 72 ppi or 7200 ppi, and the image will be the same size and look exactly the same.
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    JBHotShotsJBHotShots Registered Users Posts: 391 Major grins
    edited August 20, 2012
    Cropping at 300dpi doesn't resample up.
    Jamie
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    PeanoPeano Registered Users Posts: 268 Major grins
    edited August 20, 2012
    Cropping at 300dpi doesn't resample up.

    Correct ... at least not if you leave the print dimension windows blank. But, then, if you're not cropping for a specific print size, it doesn't matter what resolution you end up with. That was my point.

    I'm not sure why the OP is worried about resolution after cropping. Maybe he'll tell us ...
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    JBHotShotsJBHotShots Registered Users Posts: 391 Major grins
    edited August 20, 2012
    If you put 72 or 720, it won't resample; it will only use available pixels. Resampling only happens when you alter the image size in the image size function. My point to the OP was to always crop at output dpi, no matter the output.
    Jamie
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    basfltbasflt Registered Users Posts: 1,882 Major grins
    edited August 21, 2012
    yes , it changes DPI

    PS always uses your last used setting

    click on the icon left of the 2 boxes where you can fill in dimensions
    from the menu that appears choose ; size & resolution ( you can make it a preset here too )
    fill in the desired values ( 72 ) ( ok )
    accept the crop by clicking the check-mark
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    digismiledigismile Registered Users Posts: 955 Major grins
    edited August 22, 2012
    If you put 72 or 720, it won't resample; it will only use available pixels. Resampling only happens when you alter the image size in the image size function. My point to the OP was to always crop at output dpi, no matter the output.

    This has been an issue since the Photoshop cropping tool has existed. The cropping tool was designed to either just crop, or crop and resample. It indeed can upsample or down sample, depending on the selections you make in the height, width, and resolution boxes. Cropping at output dpi is no guarantee that you aren't resampling.

    Ziggy was correct that in most cases, you want to simply put in your height and width as an aspect ratio and leave the resolution blank. This is just like taking scissors and cutting away the parts that you don't want and leaving the remaining pixels exactly as they were. When leaving the resolution blank you can put in 4" by 5" or 8" by 10" or any other multiple of 4 x 5 and get the EXACT same results. It simply provides an aspect ratio to the area being cropped.

    So let's get back to what happens when we fill something in the resolution box. You can try this if you want.

    Create a new image 10" by 10" at 300 dpi. It will logically result in an image size of 3000 pixels by 3000 pixels. Now lets pretend that we want to crop the upper left quadrant of the image (i.e. a 5" square). We can easily do the math in our head and know that this space is 1500 pixels by 1500 pixels. So let's imagine several possibilities of cropping this same area.

    Now, if we put 5x5 or 10x10 or 20x20 in the height/width and NO resolution and crop this area, they will all be exactly 1500 by 1500 pixels when we crop.

    If we select 5x5 @ 300 dpi and crop, the final image size will be 1500 x1500. No change.

    If we select 10x10 @ 300 dpi and crop the same area, the final image size is now 3000x3000. We've up sampled!

    If we select 10x10 @ 150 dpi, the final crop size is 1500x1500. No change.

    If we select 4x4 @ 300 dpi, the final crop size is 1200x1200. We've down sampled.

    So, if you want to crop away part of your photo and not accidently add or drop pixels in the remaining area, leave the resolution blank! You can always change the image size on output.

    BTW, in CS6, the resolution option is gone. The crop tool acts more like the crop tool in Lightroom. You entire the height width aspect ratio, and you now have a check box to either delete the cropped area or safely hide the cropped area, in case you want to come back and change the crop.

    Hope this helps clear things up :)
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