GIMP Version: 2.6.11
Operating System: Mac OS
OS Version: XP - SP3
GIMP Experience: Beginner Level

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I have posted below a question that I originally placed within an existing thread but I am creating a separate thread for it here to solicit a greater response. Apologies to admin if this is not allowed.

Hi everyone, I have a further problem that I am experience that I hope some of you can solve for me.

When I open a project (FILE>NEW) I am presented with a dialogue box "Create a New Image" within which I am invited to determine the width and height of my project using different values such as millimeters, pixels etc. After inputting some values in millimeters, can someone explain to me why it is that when I view my template at 100% the template I see doesn't correspond to the size that I chose? The values that appear along both the top and the left hand side of the screen coincide with my selection but the template itself bears no resemblance.

To test this further, I elected to create two templates 50mm x 50mm and 100mm x 100mm within which I placed a dot in each corner to test what comes out when I print each one. As a side note, when I originally input the above values the system elected to change them to 50.4 and 100.8 respectively, why would it do that when I have specified a measurement in millimeters? Anyhow, when I printed out the above templates the resulting output again bore no relationship to the values I originally chose and in fact, the only difference between them was the size of the dots on the larger template were slightly smaller than those in the smaller template. Any suggestions?

I apologies for the tone of my questioning above but I am finding securing the obvious advantages of GIMP more onerous by the day and I haven't even started on the creative side yet! Unfortunately if I can't control the size of the design and the output, then it defeats the whole point of me using it. Hope someone can help dig me out of this hole.

Clear skies

James

Also remember that 100% zoom in Gimp is really one pixel of image on each pixel on the display device. Since you screen is about 100-120DPI, this make the image appear about 3 times bigger that it will be in print (@ 300DPI, 6 times @600DPI)

@ASTROMAN,

That's interesting... I tried the same test and entered a size of 50.00mm x 50.00mm @ 72ppi and it changed the size to 50.09 x 50.09...
I then changes the ppi to 64 and managed to get the size to 50.01mm x 50.01mm.

I've always created templates using pixels, so I've never encountered this issue, but I see that it look as though no matter what, the templates are broken down into pixels once you begin using it.

I really don't have an answer to this and don't know why it's occurring. If I want an image template of 50mm x 50mm that's what I should get, but this isn't the case.

A pixels to millimeters conversion calculator says that 189 pixels is equal to 50.00625mm... Not that this solves anything.

BTW... An image template entered as 50.00mm x 50.00mm is changed to 50.09mm x 50.09mm and give you an image template in Gimp of 142 x 142 pixels, so I don't know why the conversion calculator says 189 pixels, when 37.570833333mm is equal to 142 pixels and 188.976377953 pixels is equal to 50.00mm...

This seems to not make any sense to me.

Printing from Gimp is not WYSIWYG. If your final output is to print you should set your document canvas before you begin. The easiest way to do this is to start with a new A3-B5 or US Letter Template.
Image | Print Size is what's important, PPI should be 300+.
When you have your Print Size set-up a good option is to export as PDF and use the Adobe Reader print options.

@Odin,

I understand this, but for beginners this may be confusing when they can't even get the canvas size they want. I always work with pixels when sizing a canvas template, I can see why there's other ways of entering canvas size, but it's all broken down into pixels anyway.
ie... 'letter sized' 8.5 x 11 inch printer paper, if entered as a template in inches, will give you a canvas of 612 x 792 pixels which isn't actually an 8.5 x 11 inch canvas once it's broken down into pixels.

I'm not disagreeing, just trying to say that if I enter a canvas size in other then pixels... it's going to be converted into the nearest equivalent in pixels size as a canvas. Which is not necessarily the exact same size as what is entered an then converted into pixels.

When designing for print the main thing to understand is your canvas size and metric (px, in, mm, etc) is not the issue, it's the resolution. When you change the resolution your print width and height changes, your canvas size does not. This is why you should adjust your image size using Image | Print Size before you start. First select the resolution (print quality) and then the image size you require.

Many thanks for your kind replies.

I think I need to go away and have a play with the template system to see what I can do but the printing output side is going to need some further consideration.

Again many thanks for all your help.

James