Resizing Pure Luma Without Conversion

[SMurf]

Hello,

I'm not sure which sub-forum this would fit in, so I'm posting it here.

If I have a pure luma (Y) stream of a particular resolution (I can split it into individual frames if need be), is there any software out that will allow me to resize the frames without converting to/from RGB?

Bonus point for something that uses a high quality algorithm (splines?) :cool:

[paradoxical]

Does Avisynth not allow you to do that?

[SMurf]

Hmmm. It does support an ImageSource with pixel_type=Y8, but it's not clear whether that is luma or not (says "8-bit grayscale" in the manual) :confused:

Edit: Thinking about this... Y is 8-bit values range 16-235... if I tell a program that it's normal RGB grayscale, and get it to do high quality resize with gray samples, then export raw... that would do it, yes?

[J_Darnley]

Luma is greyscale (what is confusing about this?) so you could use avisynth. Another option is ffmpeg.

[SMurf]

Luma is greyscale (what is confusing about this?)
Lots of programs think grayscale is R = G = B.
Luma is 0.299 R + 0.587 G + 0.114 B.

Hence confusion. ;)

[Asmodian]

Avisynth 2.6 has the Y8 color space which it sounds like is exactly what you want.

[SMurf]

Avisynth doesn't seem to want to accept raw YUV frames, so I'm looking at the ffmpeg route.

I'm trying:-
ffmpeg -pix_fmt gray -s 704x576 -i frame2217.y -s 752x576 out.yuv

The output looks OK, but analysing the histogram shows that some pixels have luma values out of range (16-235).

Is there a way of intimating to ffmpeg that the input luma is TV scale, and the output should be too?

[Asmodian]

Avisynth doesn't seem to want to accept raw YUV frames, so I'm looking at the ffmpeg route.

http://avisynth.org/mediawiki/FAQ_loading_clips#How_do_I_load_raw_source_video_files_into_AviSynth.3F

[carla2013]

Lots of programs think grayscale is R = G = B.
Luma is 0.299 R + 0.587 G + 0.114 B.

Hence confusion. ;)

You are so right

[nevcairiel]

Lots of programs think grayscale is R = G = B.
Luma is 0.299 R + 0.587 G + 0.114 B.

Hence confusion. ;)

But it is. Anything else would get a colored tint.
If you assume it is, and then insert that into your equation there, the result is interesting.


R = G = B
Y = 0.299 R + 0.587 G + 0.114 B

R = G = B, subsitute all G/B with R, because they are equal
Y = 0.299 R + 0.587 R + 0.114 R
Y = R * (0.299 + 0.587 + 0.114)
Y = R * 1

Y = R = G = B


Easy math. ;)
Chroma isn't present, and the Luma alone defines the value of R/G/B