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The TIFF standards say that Group 4 encoding should use an 0.5 aspect ratio.
Yes, a square pixel has an aspect ratio of 1.0 (1:1).
Aspect ratio is not connected to resolution.
Chris
In article ,
François Robert wrote:
Yes, a square pixel has an aspect ratio of 1.0 (1:1).
Aspect ratio is not connected to resolution.
Chris
In article ,
François Robert wrote:
Dear NewsGroup,
I am wondering about the correctness of PhotoShop CS behavior in the following scenarios (under Windows):
With Kodak Imaging, (a TIFF viewer that comes with Windows), I save a line art (bitonal) raster as a TIFF CCITT Fax Group 3 or bitonal uncompressed. PS CS opens the resulting TIFF file without complaining. If I further state in Kodak Imaging my TIFF has different horizontal and vertical resolutions, and open it in PSCS, PSCS does not complain either. Furthermore the "Pixel Aspect Ratio" reported by PS CS is "square"… I have used tiffinfo and checked that the XRes and YRes are indeed different.
Now, if I save (still with Kodak Imaging) the same raster as a TIFF Fax Group 4 (with SAME horizontal and vertical
resolutions), and open it with PSCS, it complains that "Pixel aspect ratio correction is for preview purposes only. Turn it off for maximum image quality". And indeed, PSCS reports a Pixel Aspect Ratio of 0.5…
Here are my questions :
I fully expected that a square pixel would be synonymous with having equal X and Y resolutions. Apparently that is not the case. So what is pixel aspect ratio then ? And how is it connected with resolutions ?
I also fully expected that choosing a different compression scheme would NOT impact the pixel aspect ratio. Again that does not seem to be the case. What gives ?
Any comment (and/or pointers) appreciated.
_______________________________________________________
François Robert
(to mail me, reverse character order in reply address)
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