[magick-users] identify - wrong resolution

[John Culleton]

On Monday 29 June 2009 09:13:16 pm Anthony Thyssen wrote:
> On Mon, 29 Jun 2009 16:37:28 -0400
>
> John Culleton <john at wexfordpress.com> wrote:
> | On Monday 29 June 2009 12:00:30 am Anthony Thyssen wrote:
> | > On Sun, 28 Jun 2009 17:35:57 +0200
> | >
> | > Noel da Costa <noel at arc2.co.uk> wrote:
> | > | Hi,
> | > |
> | > | Thanks...  what I did was open it into Photoshop, which
> | > | reports the resolution as 300dpi.
> | > | Perhaps Gimp would do the same?
> | >
> | > BOTH would be faking it!!!
> | > Just as IM does.
> | >
> | >
> | > All of them are raster image processors.
> |
> | Therefore in Gimp one can increase or decrease the dpi figure
> | and run the dimensions up or down as you go.  The converse is
> | not true for some reason.
>
> What do you mean the converse is not true.  Of course it is true.
>
In IMageMagick perhaps. In Gimp no. The resolution remains constant 
if you adjust the  dimensions, meaning that it is doing some 
downsampling  or other conversion under the covers. It is just a 
Gimp peculiarity.   The basic rule, that size is inversely 
proportional to density holds.  But to adjust size without 
converting the raster image I have to 
adjust the density.  For example I can scan a photo at 600dpi, and 
then decrease the dpi to get a bigger image at 300 dpi. 
>    convert -density 300 file.ps  info:
>    convert -density 600 file.ps  info:
>
> would report that the 600 dpi image is twice the size (four times
> the area) as the 300 dpi version!
>
>
>   Anthony Thyssen ( System Programmer )   
> <A.Thyssen at griffith.edu.au>
> -----------------------------------------------------------------
>------------ UNIX is the spawn of the devil,
>        why he even has his deamons running the thing!    --
> Anthony Thyssen
> -----------------------------------------------------------------
>------------ Anthony's Home is his Castle    
> http://www.cit.gu.edu.au/~anthony/
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John Culleton
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