Resizing Pure Luma Without Conversion

SMurf · 28th January 2013, 22:59

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?)

28th January 2013, 23:01

Does Avisynth not allow you to do that?

SMurf · 28th January 2013, 23:15

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)

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 · 28th January 2013, 23:39

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

SMurf · 28th January 2013, 23:50

Quote:

Originally Posted by J_Darnley

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 · 29th January 2013, 00:11

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

SMurf · 31st January 2013, 01:38

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 · 31st January 2013, 02:10

Quote:

Originally Posted by SMurf

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

http://avisynth.org/mediawiki/FAQ_lo...to_AviSynth.3F

carla2013 · 13th February 2013, 15:51

Quote:

Originally Posted by SMurf

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 · 14th February 2013, 12:08

Quote:

Originally Posted by SMurf

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.

Code:

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

28th January 2013, 22:59	#1 \| Link
SMurf Registered User Join Date: Jun 2002 Posts: 32	Resizing Pure Luma Without Conversion 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?)

28th January 2013, 23:01	#2 \| Link
paradoxical Guest Posts: n/a	Does Avisynth not allow you to do that? Last edited by paradoxical; 28th January 2013 at 23:03.

28th January 2013, 23:15	#3 \| Link
SMurf Registered User Join Date: Jun 2002 Posts: 32	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) 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? Last edited by SMurf; 28th January 2013 at 23:33.

28th January 2013, 23:39	#4 \| Link
J_Darnley Registered User Join Date: May 2006 Posts: 957	Luma is greyscale (what is confusing about this?) so you could use avisynth. Another option is ffmpeg. __________________ x264 log explained \|\| x264 deblocking how-to preset -> tune -> user set options -> fast first pass -> profile -> level Doom10 - Of course it's better, it's one more.

29th January 2013, 00:11	#6 \| Link
Asmodian Registered User Join Date: Feb 2002 Location: San Jose, California Posts: 4,407	Avisynth 2.6 has the Y8 color space which it sounds like is exactly what you want.

31st January 2013, 01:38	#7 \| Link
SMurf Registered User Join Date: Jun 2002 Posts: 32	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?