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Discussion Starter · #1 ·
I'm looking at the output of my Davis DLX650 clone, from the grayscale from Avia, and it's terrible. It's not gray at all, all the ramps that should be gray are quite red. I'm ecstatic!! http://www.avsforum.com/ubb/biggrin.gif The reason is I had just downloaded a gamma table to my Davis where I increased the red by 400% - and sure enough it worked!!


OK, I'll try not to be so giddy. The summary is that I've figured out how to download any gamma ramp you want to your Davis (there are 512 points for each of R/G/B, each with a value between 0 and 8191), the change is permanent, and you don't need any dongle or anything when power-cycling the projector. Currently, I've only tried it for revision 'L' for the DLX650, but it should work for any Davis that uses similar firmware (I'm pretty confident this includes at least all Davis DLPs and their clones). Probably DreamVision too, though I'm just guessing.


I was told that all of the color adjustments in the Davis are done by the system software. Hence the implication that they could not be changed by the end-user. Well, I'd tried a bunch of other things in a desperate attempt to get gamma control of my HTPC driven projector, so hacking the system software was not beneath me. I scanned the binary to see if I could get some idea of how it works, or where the gamma ramps were. I discovered that they use WindRiver's VxWorks for their projectors' RTOS. I also discovered how to say "hue" in 7 different languages... I wasn't really sure where this was going, when I pretty much by chance happened to stumble upon sets of increasing numbers. Now that I knew what to look for, I wrote some code to scan the system software, and sure enough, I found 48 sets of exactly 512 numbers - enough for 16 RGB gamma curves. I looked at revision K software (the previous for the DLX650), and I also found sets of 512 numbers - 36 of them. So K had 12 gamma curves, and L had 16. I imagine they have something to do with the different inputs (i.e. VGA, comp1, comp2). I'm guessing that there are 4 per input, so K expected 3 different inputs, and then for some reason with L there was another input.


Anyway, I only use 1 input, I don't really care what the difference was, I figured I'd replace them all. So, I wrote another program which patched the system software with replaced gamma curves. I just wrote something simple which let you increase/decrease individually the R/G/B ramps (all 16 of them) by a percent. I first tried it with R +40%, G and B -20%. I put it on my projector, and it *seemed* that the color was redder, but I actually wasn't sure. So, I tried again with R+400%, and this time it was clear - it worked!!


Hey Milori - let's talk! http://www.avsforum.com/ubb/biggrin.gif


Mike



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Mike, you are the man!!!


My DL450 is just returning from being Thumperized on Thursday, and the last piece of the puzzle was going to be gamma table conversion.


Mark, if this breakthrough means there will be a Davis version of Dillard I will be first in line to place my order :)


Thanks again Mike for sharing your work with the forum.

As someone who can program a few lines of C code now and then but is definintely a programmer, I continue to be amazed at the technical skills of many of the members of this forum.
 

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Discussion Starter · #6 ·
Thanks for all the kind words everyone!


Hopefully Mark and I can figure out a way to figure out what gamma curve should be downloaded that *doesn't* look horrible! http://www.avsforum.com/ubb/smile.gif


Mike



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Quote:
Originally posted by mflaster:
Hopefully Mark and I can figure out a way to figure out what gamma curve should be downloaded that *doesn't* look horrible! http://www.avsforum.com/ubb/smile.gif
The only reliable and general way to acomplish this is with a calibration routine like the one Mark has put into Dilard. Even though Mike and I both have thumperized Davis PJs, the optimal gamma curves would still be quite different for our two projectors. For example, the DL450 does hot have the green shift problem, and uses a different bulb than the 650.
 

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Discussion Starter · #8 ·

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Discussion Starter · #9 ·

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Wow, those curves are awfully straight near the top. Also, it's interesting that Davis didn't use the full output range. The NEC curves fall short of the maximum as well, but not by nearly as much.


My understanding is that on the Davis units, there is a way to load the gamma tables into memory and use them for the duration the projector is turned on. The master copies of the tables are of course stored in flash. Since writing the flash repeatedly will be quite slow for milori's iterative calibration process, we should probably figure out how to load the tables directly into memory as well.
 

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Discussion Starter · #11 ·
Quote:
Originally posted by Mark Fontana:
Wow, those curves are awfully straight near the top. Also, it's interesting that Davis didn't use the full output range. The NEC curves fall short of the maximum as well, but not by nearly as much.
Straight near the top? The 'L' is flat all the way at the end, but that's at like 99% IRE...


Also, when you said "falls short of the maximum", don't pay attention to the fact that my graph goes to 9000. I think 8191 *is* the maximum, which is what they top out at.

Quote:


My understanding is that on the Davis units, there is a way to load the gamma tables into memory and use them for the duration the projector is turned on. The master copies of the tables are of course stored in flash. Since writing the flash repeatedly will be quite slow for milori's iterative calibration process, we should probably figure out how to load the tables directly into memory as well.
I didn't point out yet, I meant to, what I do is *incredibly* slow! You have to download the software, which takes a couple of minutes, and then you have to power cycle the projector!


So if we could play in Flash memory, and then only at the end use my method to update the gamma, that would definitely be an improvement. But *any* way to change the gamma on a permanent basis makes me happy.


Mike



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Discussion Starter · #13 ·
That was what I hoped! My current understanding is:
  • GeForce based HTPC, any OS - no control over gamma for the overlay under any circumstances
  • WinDVD 2.64, and WinDVD 3.0 prerelease (but not 3.0 release) - if you enable HWMC, which I think is only possible on the Radeon, you can get a Gamma slider, to set a single number for your gamma curve
  • Radeon, with ATI DVD player - you can "control the gamma". I don't think this means the whole curve, I think this is also just a single number. This might only be under WinME.


Mike



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If you do the gamma control on the PC, for each color channel you're generally mapping 8-bit values to 8-bit values, whereas if you do it on the projector, you're mapping 9-bit values to 13-bit values. So it's far more accurate to do it on the projector.
 

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Mike!

I've been away on vacation, but this is the best news I could possibly come home to.

As has been said in this thread already, YOU DA MAN!


Let us know how to do this to our Davis' as soon as you get it all straightened out...



Thanks,

Robert


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http://albums.photopoint.com/j/Album...874&a=12744078
 

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Does anybody have JVC's program to adjust the D-iLA's Gamma-moung other adjustments? I'm trying to decide if I should spring for Dilard, but my wife thinks ( and I've spent excessively) I need to draw the line somewhere and quit spending! This is neat that Davis owners can share this tweak for no financial outlay". If JVC would not be so stingy and allow owners to have access to the many adjustments, which BTW anyone who spends near 10 grand deserves, I wouldn't be asking if anyone has a way of making these tweaks for no charge. Really, any person or company that has invested in high technology deserves that last little bit of something which can make such a big difference, is this agreed?
 
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