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I'm trying to create a single image from using different single images I already have. I'm creating a new A4 document, but, when I try to open one of the images I want to add, it's smaller than the original one.

How can I open them as new layers and keeping their original size?

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  • Can you add more details? A4 standard template in GIMP is with 300 ppi, i.e. 2480x3508 pixels, and GIMP works at pixel level. Which are the dimensions (in pixel) of your images? Commented Oct 21, 2014 at 12:49
  • An example image has a 160x160 pixels, for 5x5 cm.
    – ludiegu
    Commented Oct 21, 2014 at 13:25
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    A 160x160 px image is 5x5 cm only when used at 81.28 ppi. As said, GIMP unit (as well as Photoshop one) is the pixel, and at 300 ppi your 160x160 px image is 1.35x1.35 cm. The formula is: SIZE_IN_CM cm / 2.54 inch/cm * PPI pixels/inch = SIZE_IN_PIXEL pixels; for example, 21x29.7 cm at 300 ppi are 2480x3508 px - or 5x5 cm at 300 ppi are 590x590 px. In conclusion, you need bigger images - you can resize them by scaling the layer. Commented Oct 21, 2014 at 14:20
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    I did find a simple solution with some trials and errors. I've opened the A4 new doc @75DPI, so my images are now the correct size! Grazie Paolo!
    – ludiegu
    Commented Oct 24, 2014 at 6:59
  • Ottimo! You can write your own answer, to share with other people your efforts ;-) Commented Oct 24, 2014 at 8:35

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As listed in the comments, the issue is the DPI. When using the A4 template the default DPI is 300. Your original images were created at a different DPI. A typical DPI is 72 (which is also the GIMP default), whereas for print it is generally 300 (which is what will be selected if you use the A4 template in GIMP).

As @Paolo Gibellini mentioned in the comments, the formula for DPI is

SIZE_IN_INCHES * DPI = SIZE_IN_PIXELS

(In your case, you would need to convert from CM to inches first). Using the dimensions that you provided (160 pixels for 5 CM), the DPI can be determined by solving the below:

(5 * 0.39370) * DPI = 160

Which comes out to DPI = 81. Setting your DPI do that should make your images import at the correct size.

Alternatively, you could also keep the 300 DPI (which might be desirable if the result is intended for printing) and scaling the images using the Scale Tool in GIMP instead.

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  • Can you change "The typical DPI for the web" to something like "A typical default dpi/ppi value" in order to not nurture the 72-dpi-myth? Thanks. Commented Jun 10, 2015 at 21:58
  • I've made that change. I didn't realize that there was a "72 DPI myth"... Commented Jun 11, 2015 at 18:34

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