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[OM] Re: Stolen images for sale on eBay

Subject: [OM] Re: Stolen images for sale on eBay
From: Richard Ociepka <ociepka@xxxxxxxxxxxxxx>
Date: Thu, 17 May 2007 16:33:51 -0400
Excellent explanation Chuck.

Dick


Chuck Norcutt wrote:
> Bob, you apparently don't understand the resolution number either.  The 
> 72dpi (or any dpi number for that matter) is not something that's 
> physical until it's tied to a print size.  There may be a tag in the 
> EXIF image data that says 72dpi but that's all it is... a tag.  You can 
> change it to anything you want but it has absolutely no physical effect 
> on the image.  It's an advisory value to a display or print system 
> (should such system choose to honor it) that says print or display this 
> thing at whatever physical dimension you get by dividing the horizontal 
> and vertical pixel counts by the resolution value.
> 
> Your camera does not shoot images at 72dpi.  It shoots images at 
> whatever the native image size is... in pixels.  Assuming you've chosen 
> the full size image it shoots images that are 2592 x 1944 pixels. 
> Whether the resolution tag says 72dpi or 7200 dpi doesn't change the 
> image one bit... it's still 2592 x 1944.
> 
> That said, one needs to be careful in PhotoShop with that dpi number. 
> If you change it in the image size dialog *and if* the "resample image" 
> option is checked it will have an effect on your image.  If you enter 
> that dialog with an image that is 2592 wide with a resolution value of 
> 72dpi the print size of the image will be shown as 2592/72dpi = 36" 
> wide.  If you then change the resolution to 144dpi without changing the 
> print size and also have the "resample image" option checked you will 
> increase the size of the image to 5184 pixels.  It will double the 
> number of pixel columns by interpolation.
> 
> Just remember that the image itself is nothing but *dimensionless* 
> pixels.  Dimensions only come about when we decide at what density those 
> pixels will be diplayed or printed.  Photoshop will happily add or 
> delete pixels if you allow it to in order to meet your request for a 
> certain size image at a given resolution.
> 
> Chuck Norcutt

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