GNOME Bugzilla – Bug 434171
YUV pal broadcast color space
Last modified: 2008-01-15 13:26:28 UTC
The proposed patch adds the YUV pal broadcast itu-r bt.470-4 color space to the Info Window. This allows to directly verify phase and chroma of captured color bars. Useful when transferring analog video tapes to mpeg files. The calculated values are relative to the difference between blanking and peak white level, so the normalized luma is bounded by Y = [0.0 .. 1.0] = [0 .. 100] IRE and the displayed values are in milli-units or deci-IRE. The UV phasor angle notation, Magnitude Phase, allows for conversion to QI space since the normalized phasors Cp = U+j*V, Cn = Q+j*I satisfy |Cn| = |Cp|, arg(Cn) = arg(Cp)-33 degrees. Note that NTSC-M adds a b=0.075 pedestal before broadcast through [Yb] [b+(1-b)*R] [b] [Y] [Ub]= T*[b+(1-b)*G] = [0] + (1-b)[U] [Vb] [b+(1-b)*B] [0] [V] with T the RGB to YUV transformation matrix. Depending on the capture settings one may be looking at broadcast or display values. The triple (Yb,U,V) is not uncommon since chroma circuits use the burst amplitude as reference and since the ratio (burst NTSC)/(burst PAL) = 20 IRE/(300/14 IRE) = 0.933 approximates the 1-b=0.925 scaling.
Created attachment 87186 [details] [review] YUV pal: colorframe mode and RGB -> YUV transformation.
Created attachment 87187 [details] PAL test card from 704x576 analog broadcast 100/0/75/0.
Created attachment 87188 [details] NTSC smpte bars from a pal-60 vcr 77/7.5/77/7.5 pedestal inclusive.
Created attachment 87189 [details] A UV color space illustration.
Created attachment 87195 [details] itu-r bt.470-4 The UV weigts are wub wvr PAL 0.493 0.877 NTSC 0.491 0.882 but the decoder datasheet I found states the PAL weights for NTSC.
I am not sure how useful this would be for our target user base. Perhaps this would better be implemented in an optional plug-in?
(In reply to comment #6) > I am not sure how useful this would be for our target user base. Perhaps this Well, for photo editing the YUV color space is probably not too useful. On the other hand, the luma Y has its use when modifying an image intended as background for a black on white text. Keeping the luma above e.g. 90% guarantees readability on a monochrome printout. The chroma magnitude is an indication of color presence, relative to peak white, and its phase determines the hue. But yes, this is not really informative except for captured video frames. This color space just makes setting up a pvr straightforward, and the computed values from captured testcard images agree with what is to be expected. Thus the tv->pvr->mpeg->mplayer->png->gimp setup is verified. But indeed, although I am probably not the first to give this a try, its general usefulness may be limited.
In accordance with comments, I am going to resolve this as WONTFIX. If something like this is needed, a plug-in is definitely the way to go. It is far too specialized even for our the great majority of our technically oriented users.