#NTSC Legal Colors
18 messages in this thread
I'm curious, is there a formula or rule for mixing NTSC colors using RGB or
HLS? If not, then is there some way without expensive test equipment to get
close. Maybe I'm all wet when it comes to understanding NTSC colors, someone
please straighten me out, I'm feeling alittle warpped <grin>.
Regards…….Rick (Technical Animations)
Rick:
>> I'm curious, is there a formula or rule for mixing NTSC colors using RGB
>> or HLS? If not, then is there some way without expensive test equipment
>> to get close.
The cheapest test equipment available works quite well – it is called a TV
set! Just hook your Targa or Vista to one and take a look! <g>
In terms of a formula, find a color that doesn't look right, like a shade of
red, and reduce the saturation to 50% and see how that works. It's quick,
it's real dirty, but it can get you by for most situations…
Black levels can be tougher – it's hard to visually see when pure black
exists. Try picking it up to 7,7,7 or so for the backgrounds.
Greg Pyros
Greg:
I've tried reducing the saturation levels with no significant help. Those dots
that go running around my objects, is that called chroma crawl? Will NTSC legal
colors help this problem or am I looking in the wrong place?
You lost me when you started talking about "black levels". How does this relate
to my question about NTSC legal colors?
Regards……..Rick (Technical Animations)
Rick:
>> You lost me when you started talking about "black levels". How does this
>> relate to my question about NTSC legal colors?
0,0,0 black is an illegal NTSC color. It actually falls below the bottom
threshold, and starts to conflict with other information required by NTSC
that is stored in that area…
The technical way of putting it is that a black video signal is defined at
a level of 7.5IRE (0.05V) above the blanking level. This value, also called
the pedestal, must be above the range containing the synchronizing
information, or your system will get seriously confused!
Greg Pyros
Greg:
>>The technical way of putting it is that a black video signal is defined at a
level of 7.5IRE (0.05V) above the blanking level.
It can't be as easy as keeping the material of any one object above 7.5IRE,
right? IRE must me some kind of average or mixture of any one frame that
determines this level for the video signal.
You would have to consider not only the material, but also the lighting to stay
above the 7.5 IRE, right?
If 0,0,0 is illegal, then 1,1,1 may also be illegal. If this is true, then is
there some level that you would start feeling comfortable?
If a material has say 20,30,100 one could say this material has black at a
level of 20,20,20 being that there is atleast 20 units of each color?
Am I lost in deep space, I feel as thou I'm slipping away <grin>. Do you know
if the book "Desktop Computer Animation" would explain what I'm trying to ask?
Regards…….Rick (Technical Animations)
Rick:
See if this helps: /\
/\ / \
/\ / \ / \ /
video / \ / \ /\ / \ /
signal / \ /\ / \ / \ / \/
/ \ / \/ \ / \/
/ \/ \ /
\ /
blanking —————————\–/———————-
level /\ /\ /\ /\ \/ /\ /\ /\ /\
/ \ / \ / \ / \ / \ / \ / \ / \ / \
synchronizing \/ \/ \/ \/ \/ \/ \/ \/
information ^
|
\—- trouble here!
Black Level: The level of the video signal that corresponds to the maximum
limits of the black areas of the picture.
Blanking Level: The level of a video signal which separates the range that
contains the picture information from the range that contains the
synchronizing information. The level of the front and back porches. Zero
IEEE units.
That's why you don't want your blacks too black!
Greg Pyros
Wow! Fantastic graphics! Could you do a picture of C3PO for us? Or how about
the Last Supper in Xs and Os? <g>
– Jack
Jack:
>> Wow! Fantastic graphics! Could you do a picture of C3PO for us?
>> Or how about the Last Supper in Xs and Os? <g>
Wait until you see how I animate it! <g>
Greg Pyros
Greg:
Did your experience with 3DS help the graphics <grin>. Seriouly thanks for the
help, I beginning to see some light or black as it maybe. Sounds like I need to
do some reading on this subject.
Did I read the time of your reply right 2:58 AM…..get some rest!!!!!
Regards…………Rick (Technical Animations)
<< The technical way of putting it is that a black video signal is defined at a
level of 7.5IRE (0.05V) above the blanking level. This value, also called the
pedestal, must be above the range containing the synchronizing information, or
your system will get seriously confused! >>
Any good books out there on NTSC, etc.
DannO
DannO:
>> Any good books out there on NTSC, etc.
Haven't read any yet – but the magazine AV-Video has some good information
every month…
Greg Pyros
Rick,
>>Formula for NTSC colors?
I've been looking for the answer to this one too. The closest I've come is in
my PrimeTime character generator manual:
"If you are outputting text to video, be
sure to keep your Saturation levels
below 75%, as a general rule-of-thumb;
higher levels can create NTSC illegal
colors, which will smear and bleed in
composite video."
This software works in a Hue, Value, Saturation color space, which I assume is
equivalent to HLS.
JKJ (trying to stay legal)
John:
Thanks for the info, I will try keeping the saturation level below 75%. It
looks soo… gooood in RGB, its hard to cut back <grin>. Why can't VTRs have an
RGB input, darn it.
Regards……..Rick (Technical Animations)
Rick,
If you have a Targa+, try going out to an S-V deck … the "crawl" will be
reduced almost as much as in RGB. Also, be aware that the composite encoder on
the Targa+ isn't the best out there (the ones inside the S-V decks are a lot
better). So you would end up with a much better picture if you were to copy to
a higher format and then dub down to composite.
Ang
Angelo:
I'm sending TGA images out to a Panasonic AG7750 using S-VHS, but I still can
see chroma crawl. This is even when watching the S-VHS tape, but monitoring the
VHS signal out of the AG7750. You are right thou, the chroma crawl is almost
entirely gone in S-VHS. I alway create the master tape in S-VHS, then copy to
VHS for my clients.
Thanks for the feedback, its just a matter of time before I will know
everthing….If I live to be 200 years old <grin>.
Regards…….Rick (Technical Animations)
Rick: I read your message about illegal NTSC colors and it reminded me that
I've seen an article about that subject recently …….<searching bookshelf>
….. Ok, there is an article about it in:
Graphics Gems II
Edited by James Arvo
Academic Press,Inc. 1991
ISBN 0-12-064480-0
III.6
"Television Color Encoding and "Hot" Broadcast Colors"
David Martindale and Alan W. Paeth
pp 147-158
They talk about the problems of converting RGB <-> luminance and color
difference signals and give an algorithm for detecting hot colors. It seems to
be a pretty good article.
Chris
Chris:
Would it be possible to get a copy of those articles, I suspect it would take
some time to hunt down those magazines? I would be more than happy to pay for
your coping costs. Be careful how you reply, there maybe many people that would
like to have copies <grin>.
Regards……..Rick (Technical Animations)
Rick: The article on hot broadcast colors is from the Graphics Gems II book. I
can probably arrange to connect you with this article one way or another. EMAIL
me an address.
Chris