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

So I took this fabulous picture of a sunrise - only the picture on my
iPhone is better than what I got on my camera (which I REALLY need to
learn how to use!) and I want to have it enlarged on canvas to 48"
wide by 24" tall.  The only problem is I can NOT get a good enough
quality image to have a decent end product.  I am certain that somehow
someway this can be done, because a local photo shop basically
enhanced the original image in about 5 minutes just to show me it
could be done.  I really want to do this myself so the whole process
is more cost-effective.

The problem is that I have absolutely no CLUE how to use GIMP!  I
downloaded it and even watched a tutorial, but editing functions are
grayed out and when I try to follow the tutorial my image doesn't look
anything like the step-by-step example.

If 48x24 is not an option, I at least need to know realistically the
largest I can go and keep the integrity of the photo.  Attached is the

I appreciate any help.  Thanks!

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 distance.


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. https://i.imgur.com/PM20bUL.jpg

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.

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

rich404 (via www.gimpusers.com/forums)

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