Using lower resolution image gives better result

[skerit]

I have some old DV footage I'm testing RealSR on. The source size is 1024x576 pixels. There are lots of artifacts and noise in it.

I first tried to upscale it to 4096px with RealSR, but there was nearly no improvement in the quality. It's almost a carbon copy of the original.

Then I tried something else: I downscaled the original to 512x288 pixels, and upscaled THAT to 2048px. And the result was amazing. No more noise, everything looks quite sharp, most halos are even gone, ... (The result in the headlight alone, wow.)

I uploaded the 4 images here, you can compare the 2 inputs to the 2 outputs: http://www.framecompare.com/image-compare/screenshotcomparison/7776WNNX

Now the question is: why is that? Why did I first have to downscale the image in order to get a better result? It's kind of strange, because some of the details did get lost in the conversion from the 1024px to the 512px image. Could I somehow get an even better result with the original 1024px source?

[jixiaozhong]

Thanks for your interesting try. I compare 4096px vs 2048px in the link. 2048px has less noise, but 4096px are sharper in detail. Downscaling removes noise/artifacts, so using a lower resolution will give a clean result. You can also first use RealSR, and then downscale the result. It probably generates a sharp and clean result.

[skerit]

Yeah, the 4096px version is a bit sharper, but it isn't that much better than doing a regular resize in the GIMP. Though it did remove some of the noise, too.

I'm just still amazed at the 512px to 2048px version. It's so amazing :)

[splinter21]

The downsampled 512x288 image is better visualized compared with the original one..... why?

[splinter21]

I downloaded the four images, but the resolutions are the same.