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simple question about cropping an image

May 3, 2012 5:27 PM

If I may, I'd like to know the answer to this.  For my own edification....

 

I have an image that is 16 x 24 inches.  It has a certain file size.

 

When I crop the image with the cropping tool, and set the tool to 16 inches wide by 24 inches high, the image file size increases significantly.

 

Is this what is called "resampling?"  The setting in the image size is set for Bicubic (for smooth gradients).

 

As an example, I saved the file (from a RAW conversion to jpg), and it was 14 Mb.  When I cropped it, it jumped to 19 Mb.

 

Just curious.

 

Thanks.

 

Al

 
Replies
  • Trevor Dennis
    5,942 posts
    May 24, 2010
    Currently Being Moderated
    May 3, 2012 5:33 PM   in reply to shutterdown

    Hi shutterdown (cool name)

     

    If you leave the resolution window empty, the crop tool will take on the 2:3 aspect ratio, and cut pixels rather than resample.  In fact CS6 has done away with the resolution window.  Image size can mysteriously increase after editing in Photoshop though.

     
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  • Trevor Dennis
    5,942 posts
    May 24, 2010
    Currently Being Moderated
    May 3, 2012 7:57 PM   in reply to shutterdown

    No Never resample unless you absolutely have to.  A 14Mb JPG should have more than enough pixels for most editing situations.

     

    A couple of links

    http://ftp2.bmtmicro.com/dlc/Resampling.pdf

    http://www.photoshopessentials.com/essentials/resizing-vs-resampling.p hp

     
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  • JJMack
    6,017 posts
    Jan 9, 2006
    Currently Being Moderated
    May 4, 2012 6:51 AM   in reply to shutterdown

    Though cropping is easy to understand and the cropping tool is easy to use to crop and srighten images the way the crop tool works is not fulley understood by many users.  Whey the crop tool resolution field is not empty the crop tool will resample the crop when you commit it.   Every time you resampls an image you wind up with a totally new image not a single original pixel remains intact and some image quality is lost.  Since resampling always looses some image quality you do not want to resamplae unless there is a need to.   I tell novice user not to use the crop tool till they have a good understading of basic digital image processing.  They should use the straighten tool then the  Rectangle selection tool and  menu image>crop to do cropping till then.  This will insure resampling is not being done.  I also warn them about the transform tool resamples layers to convert a layer to a smart object before transforming then. That way the can transform the layer overe and over again without accumlating image loss caused be repeatingly transforming an image.  For all transforms start from the Smart object rendered pixels not from the previous committed transform.

     
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  • Currently Being Moderated
    May 4, 2012 9:02 AM   in reply to shutterdown

    shutterdown wrote:

     

    ...

    As an example, I saved the file (from a RAW conversion to jpg), and it was 14 Mb.  When I cropped it, it jumped to 19 Mb.

     

    Just curious.

     

    ...

    Seems like your problem has nothing to to with the cropping tool or cropping at all but most likely different jpg compressions. Compressing a compressed jpg with the same level of compression will always produce larger file size than starting with a new uncompressed file.

     
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