enlarge without pixels showing for print

[mand71]

Hi,
I have an image I would like to print in big format.
This image is not sharp and shows pixels.
Which tool can I use to sharpen this image so that it looks good on a 61 x 91 cm.
Any help would be appreciated.
Kind regards,
Mandy

[PixLab]

Bare in mind that Scaling up an image would never be good... enough.
Having said that:

Image > Scale Image to your liking
Duplicate Layer
the top layer > Filters > Blur > Median Blur, around 5-7
Now, Bring the bottom layer above the one you blurred > Mode "Linear Light"
Right click on it > New from Visible > put this new layer in Mode "LCh Lightness"
Click on second layer > Duplicate > Mode "Luma Darken" or "Darken Only" (move it in the stack where you think it's best > play opacity)
Now you should have well blended pixels with sharp edges, but colors are off, at least it's a working base

Play with Opacity and visibility (the eye in front of layer) with the 3 upper layers, once you've mitigated between off colors and pixels > New from Visible > Filters > Hue Saturation > Adjust each colors independently (lightness/saturation/hue)
Then Filter > Enhance > Sharpen (Unsharp Mask)...
You can have a "map" of those those edges by putting the second layer in Mode " Difference" > then new from Visible > Put back the second layer in linear light > that new black layer put it on top of the stack and use it if you selecting the edges by selecting the black color > then invert, once selected tick the eye of that layer (no need anymore), you can use this selection in a mask (although I'll go with Threshold)

[rich2005]

Asking a lot for a bitmap editor (Gimp) to up-scale that jpeg, maybe by 7, to get an image for printing. Too many jpeg artifacts and anti-aliasing for a good result.

Another way is convert the image to a scale-able vector graphic (SVG). Still not straight forward, You need some time improving the image prior to conversion. You can use the vector editor inkscape or on-line sites for this. I used up twenty minutes but really a couple of hours would be better.

I got the attached, but it did involve a deal of pre-processing, index to reduce colors / upscale to make editing easier / at a pixel level painting out speckles / all sorts.....to  keep  the art-deco style. A note about the background color, I retained the original but for printing it should really be white. White is not printed and takes the colour of the paper, which would be that cream colour. (otherwise you use a lot of ink   )

You can import it into Gimp at any size you like, this for printing 61 cm wide (note the original proportions do not match 61 x 91).  For a printing company they should take an svg.

   

[denzjos]

Also a nice result with :
Image / Scale Image (to 61 cm x ..)
Image / Mode / Indexed / 5
Image / Mode / RGB
G'Mic-Qt / Repair / Smooth (Antilias) - play with the sliders
That's it.

[mand71]

Wow, A lot of thanks to all of you for the detailed tips en effort. I'm going to try them all. Have a great day/ evening.
Best regards,
Mandy