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Accuracy of pixel counts

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Old 11-24-2008, 02:53 PM
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Doug Nelson Doug Nelson is offline
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Accuracy of pixel counts

It's been brought to my attention that different software will sometimes report slightly different pixel dimensions for the same image. I'll admit this never occurred to me before.

Have you ever run into this?
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Old 11-24-2008, 04:50 PM
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Re: Accuracy of pixel counts

No, but I can imagine it could be so. If the dimensions are not embedded in the file header, then the application must determine it. If the programmer did not know what he/she was doing, there could be rounding errors, etc. So, if application dependent, it is also programmer dependent.
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Old 11-24-2008, 05:06 PM
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Re: Accuracy of pixel counts

When specific sizing I set my settings (crop and sizing) to 1 Pixles/inch then the exact height and width. Never gone wrong.
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Old 11-24-2008, 07:25 PM
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Re: Accuracy of pixel counts

If an image is 100px wide, the prog might be handle the numbering as 0 to 99. That's the only thing I can think of. I can't imagine a prog being off by more than 1px in either dimension.

Wait, along the lines of what Tommy said, the coder might not be handling padding properly. In most cases, an error of up to 7px. Um, I think.
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Old 12-04-2008, 05:05 PM
vlasta vlasta is offline
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Re: Accuracy of pixel counts

It is hard to imagine, that any programmer would mix the 100px vs 0-99 pixels.

On the other hand, I can imagine a situation where image dimensions stored in EXIF tags are not updated when image is resized/cropped. The architecture of EXIF is pretty bad and contains redundant info like this.

Then if an application reports the size specified in EXIF, it could be off by virtually any number.
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Old 12-04-2008, 07:31 PM
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Re: Accuracy of pixel counts

i've never seen this occur. i use paint shop pro and photoshop. granted, i use psp more, but i do use ps as well. and i've used psp for quite some years now. the only time i've ever messed up image sizes was when i used percentages rather than pixels to resize and in that case it was an operator error, not the software.
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Old 12-05-2008, 12:03 AM
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Re: Accuracy of pixel counts


You can choose something called "Pixels Aspect Ratio" - when (PS) File > New -> Advanced -> Pixel Aspect Ratio.
It is well known, especially for dtp'ers that "Pixel" is something more than "Dot".
Different device have its own specification.
Old TV sets pixels was rather round, nowadays some TV sets have oblong pixels.

Now one of the most disappointing thing in photoshop - Why when using "Smart Object" Photoshop can't render rotated pixels! (After rotation, you have a render as antialiased pixels )

Pixel is only a "specific name" not a specification.

And yes... 2 years a go, I have to work on some French stock photos - and when I open it... geometry was wrong - and after some research, I have found that it was a matter of "pixel aspect ratio"
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