[Gimp-user] New User Need Help Enlarging/Enhancing Image

Print size? 48"x 24" is a bit of a funny size. My print co. uses 24"x
20" or 30" x 20" for laser colour printing which might be better size.

However, back to the question.

First thing, Gimp is a raster editor and works in pixels which have
little to do with physical size *until* you come to print. Then a
property pixels-per-inch (ppi aka dpi) comes into play.

The ppi to use for a poster size is not the same as a 6" x 4"
photograph. Check this chart which gives advice for ppi vs. viewing


Quite a conservative value for a large poster size might be 150 ppi.

Back to your photograph: 

I would possibly straight up the horizon first but for this example.

The aspect ratio is not 48:24 (2:1) so the image needs to be cropped.
That is a matter of preference but might look like this.

Then scale the image to the required pixel size. Image -> Scale image.

At 150 ppi the image size is 7200 x 3600 pix, but you can set units in
Gimp like this. https://i.imgur.com/oP36GhJ.jpg Use NoHalo as the
interpolation method. You get a warning about size but it is just a
warning. Some operations will a little longer just be careful.

Now is the time to tweak colours etc, but for a beginner that is a
whole different question.

The final operation is always sharpening (if required) I would use
Filters -> Enhance -> Unsharp Mask and again the amount you use
depends on preference. Too much looks very artificial. Small value
like this. https://i.imgur.com/msg2H1F.jpg

Then stand back to check. https://i.imgur.com/oHfExbT.jpg

Thank you for the indepth information.  I hung on for most of it
comprehension-wise, then you lost me.  Sorry!  The reason for the large size is
because the wall we are putting it on is 7-feet wide.

nickib (via www.gimpusers.com/forums)

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