#Gamma correction
32 messages in this thread
We are currently using release 3.0 with a Truevision Targa+64
framebuffer. Using the Gamma correction feature in 3.0 we have set
the framebuffer Gamma to 1.0 with a tconfig.bat file. The on screen
set command for the framebuffer is also set at 1.0 for the closest
match on a NTSC monitor. Is this correct? What about the 2.2
recommended for output to NTSC? please help!
If your onscreen gamma in the 3DS framebuffer gamma SET dialog is
showing 1.0, it means that your Targa board is doing its own gamma
correction, and that you SHOULD LEAVE IT AT 1.0 in Studio (until you
figure out how to turn off the gamma correction on the Targa board,
of course). The problem with the Targa doing gamma correction is
that it will quantize the image (and cause banding and color
problems). I've got a message into the Truevision folks to get back
to me re this problem. When I find out how to disable gamma
correction on the T+, I'll let you know. Just remember, do NOT gamma
correct twice. That's the worst thing you could do.
Thanks for clarifying this, Gary. I've noticed the same thing with my
targa+ 16/32. The Grays match at 1.0 not 2.2. My targa+ is set for
1.0 in tconfig. as well. I take it then I should shut off the 3DS
gamma until you get a method to shut off the targa+ gamma. Maybe
Kevin Krell could jump in and add to this. I haven't had the time to
look into it closer but so far 3DSr3 is pumping out some pretty
impressive contrast ratio on a calibrated monitor across my three
peer network so I guess something's working right.
Don,
I just never got into using TCONFIG. I still use the old TMODE 11 6 0
method.
Kevin Krell – Comptuer Support Associates
Kevin,
Do you know if using tmode leaves the gamma at 1.0?
Bailey
John Ellis is suggesting an interesting way of inhibiting the T+ from
doing gamma correction. Just use the tmode 11 6 command and don't
use tconfig. Check out his message number 63782.
The bottom line is if the grays match in the 1.0 range, it means your
framebuffer is definitely gamma correcting and you shouldn't do
additional gamma correction in 3DS until you figure out how to turn
the fb gamma correction OFF. Once doing that, use the 3DS gamma
correction for much better results.
I'm using tmode 11 but not tmode 11 6. I'll try that next. I don't
know what the _6 does. So much undocumented stuff about the targa+.
Such a mystery!
Don – You need the "6" if you're using external sync, which I assume you are as
you have your own video environment. It has no effect if you aren't using
external sync as it automatically locks to internal if it doesn't get an
external signal. -JE
Thanks for the clarification on the "6" parameter. I do have a video
production suite but the CGI stuff is separate. I use the Targa+'s
sync out to genlock the diaquest DQ50P. The method described in the
diaquest manual was not as stable as the wiring I'm using. Diaquest
method produced a dropped frame about 1 in 400-500 frames. Their
engineer agreed with me that what I did was superior to their
documented method for reduction of the time delay of the sync
signal. I havn't dropped a frame since sept. 1992!
I've spent some time with this gamma thing and the jury's still out.
Seems that tmode 11 w-w/o "6" produces the same gamma level as
tconfig setting at 1.0 and 3ds on or off at 1.0. For my
understanding at this time I'll define gamma anywhere as unity
adjustment at 1.0. Meaning that 1.0 seting anywhere is as good as no
gamma delta or change. Gary is correct in that any double deviation
from the unity figure as being detrimental to the picture quality.
The targa+ manual briefly discusses gamma as "what looks good".
Rather than rely on even a calibrated monitor to determine what looks
good I've attempted to use the NTSC color bars tga file that I
uploaded to the forum some months ago. At unity gamma the color bars
produce a perfect vector image and as I adjust the gamma higher the
NTSC bars shift outside the boxes on the vector scope. This NTSC
bars file was originally created using a tektronics signal generator
and fed to the targa+ composite input with gamma set to unity for
generating a 24 bit file.
FWIW a rendering of the CHEVY.3ds produces the best looking image at
1.0 on the targa+ either using tmode or tconfig at 1.0 setting and no
gamma in 3DS3. If I turn on gamma in 3DS3 with a setting of 1.0 the
lighter colors get darker. If I adjust the gamma slider to 1.3 it
about matches the no gamma setting. I think I'll have to just
develop a self illumination NTSC color bars as real rectangle objects
for 3DS to render and evaluate with the vectorscope. I believe this
will be the only way to accurately measure this gamma thing. The
matching grays just tells me to set everything to 1.0 but I'm not
sure that produces the best looking and most legal picture.
Don,
I don't know what you mean about Targa+ info being undocumented. The
TMODE parameters are right in the manual. Where do people think I get this
stuff?
Kevin Krell – Computer Support Associates
>> I don't know what you mean about Targa+ info being undocumented.
The TMODE parameters are right in the manual.<<
Just to let you know, I can't find a single reference to
TMODE in my Targa+ 16/32 reference guide, however, it is documented
fully in a readme file in my tplus directory.
David,
Interesting. Must be a different version of the manual. Maybe it was
changed when TCONFIG shipped – my bopard is from the original release (as
dealers got the first boards shipped after the Siggraph announcement of the
Targa+).
Kevin Krell – Computer Support Associates
It seems that if you use tconfig with the 32+ the default is a gamma
1.00. The minimum value in tconfig is 0.1 However if you cold boot
your system and just use "tmode 11 6", gamma correction appears not
to be active. I have tried both configurations; using tconfig with
the batch file it creates, and cold boot alone. Using just "tmode 11
6" with a cold boot and adjusting gamma in 3DSR3, for my monitor I
get a gamma adjustment of 2.05, which I believe is correct. I also
have an old 32 which does not have gamma correction internally and on
the same monitor they appear to be adjusted equally. Hope this helps.
Thanks for that message. I was wondering about that, because although my
grey's do NOT match at 2.2 in R3, the images look WAY better. I use tmode 11
in autoexec.bat and do not use tconfig, though I did jump in and notice the
gamma slider which made me nervous.
I ended up using what I though looked best despite the grey boxes, and that was
2.2 for NTSC.
Thanks,
John Tissavary (La Luna cie)
John – I'm sure we'll learn more from Truevision, but as you say it
looks WAY better! I'm so impressed with R3. The colors POP out, I've
got Red that looks RED, nice deep and rich. The images have so much
more depth. If I find out more I'll let you know. BTW if you need to
adjust any of the other registers they can be accessed outside the
tconfig.exe manually. I'm having a blast, hope you are too 🙂 -JE
I'm so thrilled with the new renderer. It is the most outstanding
feature of 3D Studio, as far as I'm concerned. I've been comparing
Abekas/R2 output to R3/Targa+/SVO 9600, and the latter looks WAY
better! Can't wait to get to the Abekas with R3 targas! Thanks for
the word on TMODE. I don't use TCONFIG anyway, so it's no big deal.
What's the "6" for?
John – I agree it's absolutely gorgeous. I think there are a lot of
terrific new features for the animator/modeler in this new release,
but in the end IT IS the output that counts. Hmmm maybe I'll do an
ice-cream cone…. <G> -JE
Note that I found that a gamma of 1.8 worked best for Abekas output. (and the
_6_ is for turning on external genlock synching)
– G
If I understand you, will tconfig with gamma set to 1.00 do gamma
correction on a Targa+ 16/32. I use tconfig on my targa+ card with
gamma set to 1.00, and get a gamma correction at 2.10 in 3DS. As I
see it the gamma 1.0 in tconfig is the same as NO gamma correction.
When I tried to set it as low as possible, I got a BLACK screen, so
it looks like values below 1.00 produce an inverse gamma correction.
Please correct me if I'm wrong ! 🙂
Martin E. – Some people have had problems with TCONFIG, maybe for just
the reasons you mentioned, ie: they tried turning Gamma below 1.0
TMODE 11 6 works and uses the default setting. Your gamma correction
of 2.10 seems like its in the correct range for RGB, you might want
to boost it to 2.2 for NTSC output. Try using TMODE 11 6 alone and
if your rendered image looks the same with the Gamma correction
you've already set in R3, I would say you're speculation is correct.
I'm getting excellent results with whatever the default is. My
intention was to provide a working solution until there is a
definitive answer from Truevision, which I hope will be today. -JE
Martin – In answer to your question, by using tconfig.exe and setting
it for 512×486 you're putting the Targa in gamma correction mode even
though your setting is a 1.0 which is neutral (as opposed to off).
Its still going through the circuitry. Ideally you'd like to bypass
the circuitry. You'll notice that if you set your Targa 32+ to
512×400 and click on Targa32+ in the Operation mode that gamma will
go to zero. But if you click on 512×486 it automatically goes to 1.0
Which means that tconfig by default activates gamma correction even
though it is neutral. The best way is TMODE 11 6 which leaves gamma
turned off. If you need to adjust any of the other parameters you
might want like hPhase you can use Targedit instead to initialise
those functions. -JE
>Martin – In answer to your question, by using tconfig.exe and setting it for
>512×486 you're putting the Targa in gamma correction mode even though your
>setting is a 1.0 which is neutral (as opposed to off). Its still going through
>the circuitry.
I havn't tested the 512×486 resulotion as I wan't PAL not NTSC output
! I have used 512×576 (tmode 15) for my animations. I live in
Sweden, that's way I'm not a NTSC fan ! 🙂
Martin E. If you're using TMODE 15 then your board will not be setup for Gamma
Correction, which is what you want. Earlier you mentioned using tconfig with a
setting of 1.0 Most of here are not NTSC fans either <G> but its what we have
to work with for the time being 🙂 So what type of work are you doing in
Sweden? Do you have many 3DS users? Just curious. -JE
This is great news! Just the information I've been looking for.
Coincidentally, I just got through to Jamie at Truevision and he
confirmed what you said. Plus, he said that if you absolutely need
to use tconfig, you can turn off the automatic gamma correction
afterwards by doing a
targedit Byplut 1
Basically, the simplest way to not invoke automatic T+ gamma
correction is not using tconfig then… just use the tmode 11 6
parameter and all will be fine.
Fantastic! Thanks again for the info… a major Targa mystery
revealed.
Gary – You're very welcome and thank you for the new 64 bit renderer –
the colors are beautiful! -JE
I'm glad you appreciate them! <g> BTW, I made a mistake in the last
email re the targedt command line argument for bypassing the
automatic gamma if you MUST use tconfig. It's really:
targedit lutByp 1
There ya go,
Gary << BTW, I made a mistake… >> I hear the vacation Sirens
calling… Ancient Ruins, sandy beaches… quite a distraction. <G>
Two weeks and I'm outahere.
– G
The renderer is my favorite new feature in R3. I've been comparing
my R2/Abekas stuff to some R3/Targa+/SVO 9600 tests and the latter is
WAY better. Wow.
Your welcome! (the bottom line is always OUTPUT QUALITY)
– G
Gary,
My version of targedit doesn't like lutByp, but it works with lutBypass.
Bailey