It's probably a series of rounding errors when converting mm to inches and then inches to pixels. The image should have:

148mm / 25.4mmpi = 5.82677165" 5.82677165" * 300ppi = 1748.0314950000002 px

105mm / 25.4mmpi = 4.133858267716536" 4.133858267716536" * 300ppi = 1240.1574803149608 px

as you can see, not clean round number. You should have something like 1748px x 1240px which translates to roughly 148x104.99mm.

On Wed, May 12, 2010 at 6:46 PM, uluru75 wrote:

I have a problem with setting print size of images. When i set it to 148mm and 105mm, it's being set, then i save and close the image.
However, when i re-open the jpg, it often show the sizes like 148.22mm or 105.05. Basically i don't want anything after the dot, i want exact size. Does anyone has any idea how to fix it?

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On 05/12/2010 09:46 AM, uluru75 wrote:

I have a problem with setting print size of images. When i set it to 148mm and 105mm, it's being set, then i save and close the image.
However, when i re-open the jpg, it often show the sizes like 148.22mm or 105.05. Basically i don't want anything after the dot, i want exact size. Does anyone has any idea how to fix it?

Images are always saved in integer numbers of pixels.

To get exactly 148mm by 105 mm, a mm should be an exact number of pixels.

The number of pixels you mention is not exactly commensurate with a 148 x 105 mm image,
so the image (if it's really 148.22 x 105.05) will have to be scaled to be a little bit shorter.

So in the Image->Scale Image tool, select image size in mm, but don't scale it yet.

Then set the X-Y resolution to exactly number of pixels you want in a mm (10, say). This makes the specified print size come out exactly in pixels.

Then, click on the chain link on the Image Size x-y pair, so the image can be scaled to exactly the dimensions you want. Notice that 72 pixels per inch is 2.8346567 pixels/mm.

Now, enter 148 in the Width textbox and 105 in the Height textbox (the pixels/mm entry should not change). NOW, scale the image. On this user list, people have mentioned a few times that the best scaling quality seems to be Sinc (Lanczos3) interpolation, but YMMV.

Actually, when I did this with a 3872x2592 pixel image, then saved and reopened the image, it reopened with the image size default set to inches, and then when I converted that image size to mm, it said 148.01 x 105.01. Then, when I clicked in the pixels/mm box, then the height box, the .01's went away by themselves. This suggests it was a rounding error, rather than a size problem.