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Cropping an image to make it larger?

Mar 12, 2012 6:27 PM

When cropping an image by using a specified W and H in the Crop options that are larger than the image, is Photoshop actually increasing the W and H of the image by stretching those pixels?

 

Thanks.

 
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  • Noel Carboni
    23,526 posts
    Dec 23, 2006
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    Mar 12, 2012 6:31 PM   in reply to media kat

    Yes, it will resample to the size you've specified after cropping off the parts you have left out of the rectangle.  It's supposed to be a time saver.  But the resampling is just using the Bicubic method Photoshop provides, so if you increase the pixel count you'll just have a bigger, fuzzier image.

     

    -Noel

     
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  • Noel Carboni
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    Mar 12, 2012 7:58 PM   in reply to media kat

    You'll want the Resample box checked (enabling resampling) if you want to change the pixel count.  An example of when you might want to do this is for downsizing an image to be published in a particular size on the web.

     

    If you're just trying to change size at which it will print, chances are very good that you would not want to resample.

     

    If you're at all shaky on the subject, it would be good to get your head completely around what pixels are and how they make up an image - that way rather than try to remember rules of thumb for when to use what checkbox you'll understand the reasons for doing things and can make the best decisions given your needs.

     

    -Noel

     
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  • Noel Carboni
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    Mar 12, 2012 8:37 PM   in reply to media kat

    I'd say as a general answer, yes, there is a downside.

     

    I've always been of the school that more resolution is better.  If you have a 4000 x 6000 pixel image and you print it at 4 x 6 inches, some would say 1000 ppi is overkill, but I say why arbitrarily limit the resolution if you've already got it?  It's possible (depending on various factors) that the print could come out looking a little better at 1000 ppi than, say, 300 ppi.

     

    My suggestion is to always keep a digital image's pixel count in mind first and foremost, then make everything else work with that.  It's hard to go wrong doing that.

     

    -Noel

     
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  • Currently Being Moderated
    Mar 12, 2012 11:42 PM   in reply to Noel Carboni

    Well yes it is. The pixel count needs to have a whole number relationship to the native dpi of the printer, if printing is what you are after. For Epson, it's 720 dpi, for Canon it's 600 dpi. So if  I scale up to print, I'm usually no larger than 720, because the printer will have to interpolate between the supplied pixel count and the printer's native count. And, AFAIK, going to say 1440PPI shows no additional quality gain, even though the printer itself may go to 1440 (2880 in one dimension for really high end printing.). But maybe this is due to camera quality. If I were using Canon, I would be in multiples of 300. Epson, multiples of 360. My RAW output is set at 360.

     

    And for cropping, I never have a number in the Resolution box. I wait until I print to decide that.

     
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  • Pierre Courtejoie
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    Jan 11, 2006
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    Mar 13, 2012 2:37 AM   in reply to Noel Carboni

    Noel, there are some cases with repeating detail where downscaling an image with too much resolution might hurt the ifinal mage. Dan Margulis  (I know he is fond of creating debatable statements, but he had an image as a proof in this case) illustrated this problem in this document: http://www.ledet.com/margulis/Makeready/MA25-Resolution.pdf page 306 (but the PDF compression makes the images useless, I remember it on the ledet website as a webpage, the difference was clear.

     
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    Mar 13, 2012 1:10 PM   in reply to media kat

    media kat wrote:

     

    Thanks for the tips. Just to understand a bit more before I do my own readings, is there any downside/con to keeping the Resample box unchecked all the time when making images smaller in size whether intended for print or on screen display?

     

    Thanks.

    For on screen display (monitors and display devices) if you don't have the Resample box  checked, changing any of the other settings makes no difference to the image - the pixel count (number of pixels per side) remain the same and thus the size of the image on monitors and display devices unchanged. The size of your image when displayed on monitors and display devices at 100% zoom will fit each pixel from your image to each pixel of the screen. Thus the size of your image in spatial units (like inches) is determined by the size of the screen pixels of the displaying device.

     

    For printing, when the Resample box is not checked, you can think that changing the size with spatial units is like determining how big the pixels should be when printed.


    When reducing pixel count, for Resample Image, try Bicubic Sharper (best for reduction)

     
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  • Trevor Dennis
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    May 24, 2010
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    Mar 13, 2012 1:19 PM   in reply to media kat

    There is also the trick of dragging the crop handles _outside_ the exisiting image limits which adds Canvas size.   Probably a wee bit quicker than using Ctrl Alt c and entering values.

     
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    Mar 13, 2012 2:12 PM   in reply to Trevor Dennis

    Hudechrome: Epson uses the large dpi count ( now 5760 horizontal) to form color cells . It is probably a good idea to send an Epson 360 ppi, though.

     
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    Mar 13, 2012 2:43 PM   in reply to Lundberg02

    Link, please?

     
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  • Noel Carboni
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    Mar 13, 2012 7:58 PM   in reply to Pierre Courtejoie

    Printer driver algorithm quality has changed a good bit in recent years.  Time was you had to use Qimage to get the very best prints.  Have you noticed that no one's recommending that any more?

     

    I suggest doing your own tests, and look at the results critically, rather than relying on what someone else did 15 years ago.  I did, and I stand by what I said.

     

    It might well be that you have a printer driver / printer hardware that prefers a specific ppi.  And it might be that your printer driver will take care of it for you very nicely indeed.  In the latter case, why put extra effort into pre-sizing your image?

     

    One needs to question rules of thumb from time to time.

     

    Perhaps I'll do some comparitive tests and photograph the results.

     

    -Noel

     
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  • Currently Being Moderated
    Mar 13, 2012 8:40 PM   in reply to Noel Carboni

    15 years is an eternity in digital.

     
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  • Currently Being Moderated
    Mar 16, 2012 5:58 AM   in reply to media kat

    There are more down sides but there are some upsides to.

     
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