[ajp2k14]

Is something like lanczos/spline/catmull-rom possible or are they completely different algorithms?

I think for catmull-rom you want something like:

Code:

vcgencmd scaling_kernel    0 -4 -8 -14 -18,-19,-16 -8  9 39 77 122 166 206 237 255
255 237 206 166 122  77  39   9  -8 -16 -19 -18 -14  -8  -4   0

But it's probably got too much overshoot. These kernels are operating on the [4:2:0] output of the codecs, which is encoded with gamma. So the effect is exaggerated in linear light on the monitor.
Kernels with nice mathematical or signal-processing properties don't always look best.

Interesting, thanks! I'm just trying to translate my experiences with MadVR scaling to the Pi. Catmull-rom is probably better for downscaling though, in fact I think it's the recommended method in MadVR for downscaling (in linear light).

It would be interesting to see more Lanczos variants, lanczos3 is a good compromise between sharpness and ringing I think. MadVR probably has more tricks when scaling and converting so it's probably not scaling gamma encoded video... ?

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Here's another suggested by the image scaling guy (you can just enter that while video is playing):

Code:

vcgencmd scaling_kernel   0  -4  -8 -14 -18 -19 -16  -8   9  39  77 122 166 206 237 255 255 237 206 166 122  77  39   9  -8 -16 -19 -18 -14  -8  -4   0

It's a cubic with A=-0.5.

I've tried comparing +4 (0.08, Blackmann), +7 (0.14, Mitchell Netravali), cubic with A=-0.5, and lanczos with A=2 and I'm not seeing any significant difference between them - they're all quite similar, all being sharper than the default +0/0.00. Very hard to say which is best. This is while viewing text on SD/xvid material.

I think you have to sit very close to the TV to notice the differences between some of them and concentrate on text, diagonals and textures? It would be interesting to try Lanczos with A=3 and perhaps even A=4 and perhaps Jinc with A=3 too if possible. Those ones produce very good results in video players on the PC at least. I read that Intels HD Graphics (at least 4000+) uses something like Lanczos3...

I mostly watch 720p and up though so not sure which one is best for SD...