Photoshop CS changes my document size

JL
Posted By
Joanna_Lakey
Feb 14, 2004
Views
340
Replies
6
Status
Closed
This is very strange. I need to create a new document that is exactly 55.50mm x 41mm. I enter the numbers in the fields, click OK and all goes well, but when I then go to image / size, it shows the document as being 55.63mm by 40.98mm! I did this a couple of times to be sure I wasn’t entering the wrong numbers and I’m not. I also tried to "trick" photoshop to making it the right size using the crop tool but the same thing happened. I enter the size I want in the crop fields and do the crop – then again check the image / size and the document again shows the wrong size! I’m really curious if anyone else has run into this. I know this is a very unusual project to require such specific sizing, but I wouldn’t think it should be a problem for this software to do it.

Thanks in advance!
Joanna
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P
Phosphor
Feb 14, 2004
You’re creating a file using millimeter dimensions.

Photoshop, and all other raster-based graphics applications, are internally coded to base all distance measurements on units of pixels, and will convert that absolute value of pixel measurement into millimeters, inches, etc, behind the scenes and on-the-fly.

In raster-based images, the pixel unit is the smallest possible division of distance. You can’t have a fraction of a pixel.

When you enter a length value using any other unit of measurement, as you have done, Photoshop will internally convert that value into pixels, then display that length in your measurement unit of choice, rounding it off to the nearest value that defines the length without leaving a fraction of a pixel as a remainder in the result.

Want better accuracy? Start out at a higher resolution for your image, then reduce physical dimensions when you’ve finished working on the image.
JL
Joanna_Lakey
Feb 14, 2004
Thanks! That makes perfect since! I appreciate the advice on using a higher resolution to work on too.

Joanna
P
Phosphor
Feb 14, 2004
Great, Joanna.

Sometimes that’s a difficult concept to explain, and for some folks to wrap their head around. Once it sinks in, it makes simple sense.

Might be a good idea to me polish that explanation and save it as a text file so I can paste it, as needed, when anyone else asks.

::Phos finds himself a little project for a boring Saturday afternoon::
MM
Mick_Murphy
Feb 14, 2004
Please do that Phosphor. I’ve seen this many times and never understood it before. Thanks for the clear explanation.
RW
Rene_Walling
Feb 14, 2004
Want better accuracy? Start out at a higher resolution for your image, then reduce physical dimensions when you’ve finished working on the image.

Another way to get exact measurements is to work at a resolution that matches your document size (ie pixels/centimer when working with metric units and pixels/inch when working with imperial units)
JL
Joanna_Lakey
Feb 15, 2004
Thanks Rene! That should work great and I never would have thought of it.

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