[FFmpeg-devel] [Bulk] Re: [PATCH] smptebars filter

Tim Nicholson nichot20 at yahoo.com
Mon Aug 6 10:57:28 CEST 2012


On 06/08/12 09:32, Stefano Sabatini wrote:
> On date Friday 2012-08-03 16:02:53 +0200, Stefano Sabatini encoded:
>> On date Friday 2012-08-03 08:59:56 +0100, Tim Nicholson encoded:
> [...]
>>> My values are based upon:-
>>> 0 IRE units= 0; 100 IRE units= 255; RGB
>>>
>>> For the pluge section this gives
>>>
>>> black= 255*7.5/100 = 19.125    => 19
>>> black-4= 255*3.5/100 = 8.925   =>  9
>>> black+4= 255*11.5/100 = 29.325 => 29
>>>
>>> For the Q,-I sections
>>>
>>> Using the Rec 601 coefficients (ffmpegs default RGB to YUV matrix)
>>>
>>> Q:/  RGB 67,  0, 130 => YUV 46, 175, 148 (after rounding)
>>> -I:/ RGB  0, 68, 114 => YUV 61. 158.  95 (after rounding)
>>>
>>> The "correct" values being (see the avisynth page or poynton for
>>> detailed maths)
>>>
>>> Q:/  YUV 16, 175,148
>>> -I:/ YUV 16, 158, 95
>>>
>>> Which leads to my submission:-
>>>
>>>
>>> static const uint8_t white[4] = { 255, 255, 255, 255 };
>>> static const uint8_t black[4] = {  19,  19,  19, 255 };
>>>
>>> /* pluge pulses */
>>> static const uint8_t neg4ire[4] = {   9,   9,   9, 255 };
>>> static const uint8_t pos4ire[4] = {  29,  29,  29, 255 };
>>>
>>> +/* fudged Q/-I */
>>> static const uint8_t i_pixel[4] = {   0,  68, 130, 255 };
>>> static const uint8_t q_pixel[4] = {  67,   0, 130, 255 };
>>>
>>>
>>>
>>>>
>>>> (And I agree if we call it "SMPTE bars" I'd expect the pattern refers
>>>> to some standard).
>>> ...and as we are fudging some values I think we should say so as per my
>>> inline comment above...
>>
>> Patch updated against the proposed values. In order to avoid the Q/-I
>> color "fudge" we could find some hack to tell ff_draw_color() to
>> accept YUV values and convert them to RGB colorspace, but I'm not sure
>> I'm willing to do the work...
>> -- 
>> FFmpeg = Friendly and Forgiving Martial Puristic Elfic Gem
> 
>> From dadb5afd57ee0299df6dd456d2d93da4675d417e Mon Sep 17 00:00:00 2001
>> From: Paul B Mahol <onemda at gmail.com>
>> Date: Wed, 20 Jun 2012 01:54:58 +0000
>> Subject: [PATCH] lavfi: add smptebars source
>>
>> Patch readapted by Stefano Sabatini, color values proposed by Tim
>> Nicholson <nichot20 at yahoo.com>.
> [...]
> 
> I'm going to push the patch tomorrow if nobody has objections.
> Tim?
> 

Fine by me.

BTW I now have a copy of the latest SMPTE spec for the SD/HD bars, so I
will see what it will take to implement them since they will be
potentially more useful. However I am about to go on my holidays so it
will be a while and I don't want to hold things up anymore...

-- 
Tim




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