Need help: filter pixelation and compression artefacts on upscale

[Chocobo]

Hey there,

I am doing a presentation of a painting in a realistic comic style. Unfortunatly I have to upscale the image x8 and that leaves me with ugly pixalation and compression artefacts.

Can someone suggest how I can treat the picture to hide those artefact, while taking the least invasive proceedour. I dont want to alter the original look too much. This is the problem I am dealing with:

[rich2005]

More information please.
Which operating system Windows 7 / 10 / 11 or linux or MacOS ?
Are you really using Gimp 2.8 ? That can limit options
Is your image (jpg 722 x 721 pix) a clip from the times 8 up-scaled image or is it part of the pre-scaled image ?

[Chocobo]

(04-27-2022, 11:48 AM)rich2005 Wrote: More information please.
Which operating system Windows 7 / 10 / 11 or linux or MacOS ?

Are you really using Gimp 2.8 ?  That can limit options
Is your image (jpg 722 x 721 pix) a clip from the times 8 up-scaled image or is it part of the pre-scaled image ?

Win10. Im sorry I should have checked before. It is 2.10.28. Here I provide an image of the exact scale I need. I want to display it on a large 4k screen.

[rich2005]

That is the final size ?

I can not see any pixelation. Scaling up x8 does introduce a certain fuzzyness. You can change the interpolation to LoHalo (default is Cubic) but I do not think that will make much difference.

Compression artefacts ? I can not see any of those either, try changing your format to other than jpeg.

You could try the gmic plugin http://www.gmic.eu It does contain upscaling filters, although mostly x2 There is one Upscale (diffusion) in the repair section. Sharper than a regular x8 upscale but you might not like the 'effect'

Otherwise, I do not know. There are oneline "smart / AI" but most seem to charge.

Keep looking-in, someone will have better suggestions.

edit: Just a note about exporting jpegs. The relationship between file size and quality is not linear, There is very little difference in quality between 95 and 100 but the file size will be much smaller. jpeg 100 is not lossless. You could try exporting as a webp format.

[Chocobo]

(04-27-2022, 04:06 PM)rich2005 Wrote: That is the final size ?

I can not see any pixelation.  Scaling up x8 does introduce a certain fuzzyness. You can change the interpolation to LoHalo  (default is Cubic) but I do not think that will make much difference.

Compression artefacts ? I can not see any of those either, try changing your format to other than jpeg.

You could try the gmic plugin http://www.gmic.eu It does contain upscaling filters, although mostly x2 There is one Upscale (diffusion) in the repair section. Sharper than a regular x8 upscale but you might not like the 'effect'

Otherwise, I do not know. There are oneline "smart / AI" but most seem to charge.

Keep looking-in, someone will have better suggestions.

edit: Just a note about exporting jpegs. The relationship between file size and quality is not linear, There is very little difference in quality between 95 and 100 but the file size will be much smaller. jpeg 100 is not lossless. You could try exporting as a webp format.

Well I see the image 4k on a big screen in full screen mode it is extremly muddy, and there are these cube shapes everywhere. Can't you see that?

[rich2005]

Quote:Well I see the image 4k on a big screen in full screen mode it is extremly muddy, and there are these cube shapes everywhere. Can't you see that?

Maybe, but I do not have anything to compare it to. Can you post the original small (pre-scaled) image.

[Chocobo]

(04-27-2022, 06:16 PM)rich2005 Wrote:

Quote:Well I see the image 4k on a big screen in full screen mode it is extremly muddy, and there are these cube shapes everywhere. Can't you see that?

Maybe, but I do not have anything to compare it to. Can you post the original small (pre-scaled) image.

If you want a comparison a painting would be an adquate one. The scan is unfortunatly 8 times to little resolution and was exported as jpg. It is simply not hires enough and there is jpg compression. I want a look that is more like the real item.

[rich2005]

Quote:If you want a comparison a painting would be an adquate one. The scan is unfortunatly 8 times to little resolution and was exported as jpg. It is simply not hires enough and there is jpg compression. I want a look that is more like the real item.

Sure I can do that. Using your image as an example, an image search brings up plenty of equivalent 'paintings' in small sizes.

Small size as downloaded (480x270) and zoomed in to 800% which of course shows the individual pixels. https://i.imgur.com/j4zu89K.png

If that is what you want scaled x8 (3840x2160) then using Interpolation None will keep the pixel shapes. https://i.imgur.com/my9pnfA.png but you were complaining about pixelation.

A more usual x8 upscale using LoHalo which interpolates the pixels is as expected a bit fuzzy. https://i.imgur.com/a1aXCQd.png but no pixelation.

... and this as mentioned the gmic upscale, very slightly sharper, x8 is a big jump. https://i.imgur.com/bNi5Fhr.png

Since you say it comes from a scan, nothing you can do about original quality. You would be better off getting a better scan and not using jpeg output. Most scanners will output a tiff. If that is not possible try improving the scan before upscaling, The gmic plugin again has filters JPEG smooth and Unquantize to try and repair.

Generally, a sad fact, poor image in = poor image out (trying to be polite here )

edit: This a screenshot of the gmic unquantize filter, removes artifacts but it is akin to smoothing. https://i.imgur.com/dcRRQNf.png

[Chocobo]

(04-27-2022, 07:44 PM)rich2005 Wrote:

Quote:If you want a comparison a painting would be an adquate one. The scan is unfortunatly 8 times to little resolution and was exported as jpg. It is simply not hires enough and there is jpg compression. I want a look that is more like the real item.

Sure I can do that. Using your image as an example, an image search brings up plenty of equivalent 'paintings' in small sizes.

Small size as downloaded (480x270) and zoomed in to 800% which of course shows the individual pixels. https://i.imgur.com/j4zu89K.png

If that is what you want scaled x8 (3840x2160) then using Interpolation None will keep the pixel shapes. https://i.imgur.com/my9pnfA.png but you were complaining about pixelation.

A more usual x8 upscale using LoHalo which interpolates the pixels is as expected a bit fuzzy. https://i.imgur.com/a1aXCQd.png but no pixelation.

... and this as mentioned the gmic upscale, very slightly sharper, x8 is a big jump.  https://i.imgur.com/bNi5Fhr.png

Since you say it comes from a scan, nothing you can do about original quality. You would be better off getting a better scan and not using jpeg output. Most scanners will output a tiff.  If that is not possible try improving the scan before upscaling, The gmic plugin again has filters JPEG smooth and Unquantize to try and repair.

Generally, a sad fact, poor image in = poor image out (trying to be polite here  )

edit: This a screenshot of the gmic unquantize filter, removes artifacts but it is akin to smoothing. https://i.imgur.com/dcRRQNf.png

Thank you very much. I will try to copy your steps and get gmic upscale. Thanks for the examples. Nice illustration! Looks way better.

Yes I would prefer a better scan but the artist seems to be unable or incapable of providing a better one.

If I run in any trouble I will report on that. If it works I will show the result.

[denzjos]

Maybe this free software to enlarge images can help you : https://www.reshade.net