Shadow detail/gamma enhancement for the analog sources - Page 4 - AVS Forum
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post #91 of 492 Old 09-10-2005, 07:01 AM
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Yup, now you're spot on :)

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post #92 of 492 Old 09-10-2005, 07:10 AM
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post #93 of 492 Old 09-12-2005, 11:15 AM
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Quote:
Originally Posted by tse
The green channel and the DC restore stuff is together.

A few pictures.

A stairstep pattern with the top trace being the input, the bottom is the output.
Thanks. I'm a little bit confused about these. What range are they showing? If it is from 0%stim to 100%stim then these are different than I was expecting. I thought these were going to affect just things under 5%stim (or so) as much as possible and try to leave the rest of the gamma curve mostly intact. If it is raising up the curve even up to 40% stim or so then this is different and I think it would lower the 3-Dimensionality in many mixed scenes. But then it may just be that I'm not understanding what this is showing, as I mentioned.

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post #94 of 492 Old 09-12-2005, 05:53 PM - Thread Starter
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The images do show 0 to 100%. So far it looks pretty good but I am going to move the "expansion" down a bit lower and increase the amount of gain. A couple of resistor value changes.

The TL082 opamps proved to be a poor choice. I lucked out on the green channel but the red and blue had a bit of an offset error that led to the video being clamped at about 50mV above zero volts. LT1213 would be a better choice.
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post #95 of 492 Old 09-16-2005, 09:37 AM - Thread Starter
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I'm going to drag it out one more time and then I'll leave it alone. If you are not using HTPC or other sources that allow gamma adjustment, this circuit will make a significant difference. It has always been necessary to turn up the brightness level with your CRT projector to see the details in shadows and dark scenes. Then when a "black" scene comes along you notice a gray raster up on your screen. I've been watching my 480P DVD for about a week now with the gamma circuit working and with the projector brightness adjusted so the shadow detail is present the projector goes completely black on black scenes. There is a noticable improvement in dynamic range.
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post #96 of 492 Old 09-16-2005, 09:53 AM
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post #97 of 492 Old 09-16-2005, 11:13 AM
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Hi tse,

Sounds like it working like you expected. Did you redo the values to move the expansion down and change the gain, what values are you using now.

What opamp are you using now instead of the TL082, maybe try the TLE2082, its the newest version of the old TL0 series.

Walter

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post #98 of 492 Old 09-16-2005, 01:39 PM - Thread Starter
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Quote:
Originally Posted by WTS
Hi tse,

Sounds like it working like you expected. Did you redo the values to move the expansion down and change the gain, what values are you using now.

What opamp are you using now instead of the TL082, maybe try the TLE2082, its the newest version of the old TL0 series.

Walter
Walter,

The original values are still there. It looks good like it is but I'll probably play around with it before all is said and done. The opamps that control the DC restore level (TL082) were a poor choice because their input offset voltage could be 10 or 13mV! Any dual op-amp with input offset less than 1.0mV and a slew rate better than about 4V/uS should work just fine. For best results pin 5 of those opamps should be connected directly to ground and eliminate the two 10K resistors that go between +/-5V. There was one mistake on the circuit board. I missed connecting pin 1 of the LM311 comparator to ground.

Person99,

All the information except the parts list is at the start of this thread. I'll be happy to help if you would like to build one for yourself.

Scott


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post #99 of 492 Old 09-16-2005, 01:45 PM
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Hi Scott,

I thought there was mention made that the values were alittle hot, too much correction and thats why you were going to knock them down abit. So how does this differ from an actual gamma circuit in what it gives you at the end of the day so to speak.

Ouch, 10 - 13mV of input offset, thats terrible for a fet input opamp, I can't remember the last time I looked at the specs for that series but I wouldn't have guessed that bad. Yeah you don't need a super performer for that app but one thing you do want is good dc specs.

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post #100 of 492 Old 09-16-2005, 01:57 PM
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Quote:
Originally Posted by tse

Person99,

All the information except the parts list is at the start of this thread. I'll be happy to help if you would like to build one for yourself.
Thanks, I was hoping we could co-ordinate the run of boards here or if someone wanted to build them and plop them in a case and sell the (in other words, you--to make some money to reimburse the time spent).

If not, I'll just order boards and stuff them myself.

Dave
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post #101 of 492 Old 09-16-2005, 02:05 PM
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I think MP has an interest in this. Whether that interest is building a MPtse unit, I don't know. CJ is close by. Maybe tse and CJ could hook up and build some units.

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post #102 of 492 Old 09-16-2005, 08:05 PM
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G'day :)

I mentioned in an earlier post about the progress my mate was making with his solution to this gamma problem and he has now finalised the design. He's incorporated all 3 colour circuits onto the one board and it will be powered by a standard powerpack that is universally available in any country.

Below is a diagram depicting the range of adjustments available via the internal pots. The blue line is the maximum you can get out of it and one of the adjustment pots allows a curve anywhere between this blue one and the straight line to be created. The green is a curve of 2.0 for example. The point where the curves meet at the top (which is 1.0V on this diagram) can be adjusted as well to being it down to the correct 100IRE level (0.7V for example ). This will benefit some projectors which like a slightly higher input signal.

It should be obvious that this is a true gamma correction circuit and should be of particular benefit to those not running a HTPC. It will still be of significant value to those using a HTPC as the curve is infinately variable and exhibits less noise at the bottom end.

This project is a labour of love essentially but he has indicated he is prepared to run off a small batch of these and assemble them into a small case if numbers are sufficient to warrant it. He has access to an automated SMD assembly machine and can produce these for minimal cost. The pricing would depend upon the interest shown so if you are considering something like this shoot me a PM or indicate on this thread. He's not out to make a profit from this venture but wants to cover his costs. Initial thoughts are that he can produce the whole assembly for under US$200.

When I next catch up with him i'll take a piccie of the final circuit board and some CRO traces. For those who don't know one end of a soldering iron from another this will provide an alternative to TSE's design.

Cheers

Russ

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post #103 of 492 Old 09-16-2005, 08:56 PM
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I'd be interested in either design. Though I don't full understand gamma or the technical details, I'm all for better details in the shadows with cranking the brightness. :) I know which end of the soldering iron to hold :eek: but I'm more the toaster repairer than the electronics builder. :o I'm sure I could find some one to build tse's design but a turn key product is more my style. ;)

I'd also like to see a few reviews of tse's and benny's mate's designs. Not that I don't trust either of you guys. I just value other opinions before I lay down my hard earned cash.

Russ - what's the input and output of your mate's design (RGBHV, component, VGA. etc.)? OK! I reviewed the thread from the beginning and found the test bench pics. Looks like input & outputs are BNC for RBG. I assume the H & V are handled also?

tse - I'd ask the same question. I see 4 BNC connectors and plug in connector.

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post #104 of 492 Old 09-16-2005, 09:22 PM - Thread Starter
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Quote:
Originally Posted by PAW
I'd be interested in either design. Though I don't full understand gamma or the technical details, I'm all for better details in the shadows with cranking the brightness. :) I know which end of the soldering iron to hold :eek: but I'm more the toaster repairer than the electronics builder. :o I'm sure I could find some one to build tse's design but a turn key product is more my style. ;)

I'd also like to see a few reviews of tse's and benny's mate's designs. Not that I don't trust either of you guys. I just value other opinions before I lay down my hard earned cash.

Russ - what's the input and output of your mate's design (RGBHV, component, VGA. etc.)?

tse - I'd ask the same question. I see 4 BNC connectors and plug in connector.
My board has RGB and Hsync inputs. There are RGB and Hsync outputs. I think both projects are attacking the same problem. Low shadow detail without elevating the black level to a "gray' level. This is something that has been missing from the very beginning of CRT projectors. Wish I had thought this up five years ago when I could have made major bucks from it.
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post #105 of 492 Old 09-16-2005, 09:55 PM
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I'm still a bit unclear why this is a fundamental issue with CRTs. Is the gamma on CRTs just basically wrong for proper shadow detail? Due to the physics of the phosphors or whatever? If that was the case, I don't understand why at least some CRT manufacturers didn't incorporate a gamma correction circuit in their projectors. Guess they weren't really aiming them at the video market, and the target market didn't worry too much about shadow detail?
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post #106 of 492 Old 09-16-2005, 10:56 PM
 
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In my case it is not using an HTPC or a scaler per say with gamma adjustments . Put me down for one when a universal working unit is available ! :)
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post #107 of 492 Old 09-17-2005, 02:07 PM - Thread Starter
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Quote:
Originally Posted by garyfritz
I'm still a bit unclear why this is a fundamental issue with CRTs. Is the gamma on CRTs just basically wrong for proper shadow detail? Due to the physics of the phosphors or whatever? If that was the case, I don't understand why at least some CRT manufacturers didn't incorporate a gamma correction circuit in their projectors. Guess they weren't really aiming them at the video market, and the target market didn't worry too much about shadow detail?

The CRT is not a linear device. A certain drive level will produce a certain light output but doubleing the drive does not necessarily double the light output. CRTs are most non-linear at the lower light output end. I'm not sure why the CRT projector seems to aggravate this situation but it has always been thus. A little boost in the shadow detail part of the video helps.
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post #108 of 492 Old 09-17-2005, 02:34 PM
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There are a few HTPC experts on this forum and I would think they have this issue nailed using the newest Radeon or nVidia 6600GT forceware drivers.
The gerneral concensus so far is to leave video card levels alone and do all the tweeking in Theater Tek.

From what you all said, this electronic device can fix the signal levels in such a way that the HTPC video card cannot? Right now I switch my VGA output from the video card to an Extron which converts it to 5BNC cables. What would you do in this configuration?

Oops. The answer to my question was also answered above. Sorry :)

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post #109 of 492 Old 09-17-2005, 02:50 PM
 
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Quote:
From what you all said, this electronic device can fix the signal levels in such a way that the HTPC video card cannot? Right now I switch my VGA output from the video card to an Extron which converts it to 5BNC cables. What would you do in this configuration?
No, this card is for users who don't have other means of gamma adjustment in their system, i.e. they are using HD boxes, upconverting players etc etc that don't have high quality(if at all) gamma adjustments. If you are using an HTPC, you can tweak gamma in the video card quite easily and implemented well.
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post #110 of 492 Old 09-17-2005, 03:28 PM
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Quote:
Originally Posted by stylinlp
There are a few HTPC experts on this forum and I would think they have this issue nailed using the newest Radeon or nVidia 6600GT forceware drivers.
The gerneral concensus so far is to leave video card levels alone and do all the tweeking in Theater Tek.
My TheaterTek with 6600GT doesn't have gamma adjustment. TT2 had gamma control when I was using a 9700 Pro video card, but when I installed the 6600GT, that feature disappeared. :confused:

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post #111 of 492 Old 09-17-2005, 05:00 PM
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Phil do you have Gamma in the display properties? If not, try Powerstrip.

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post #112 of 492 Old 09-18-2005, 10:31 AM
 
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Indeed Phil, it should be on the card, adjust there.
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post #113 of 492 Old 09-18-2005, 12:01 PM
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Benny's diagram shows that his particular device affects the entire gamma curve, much like adjusting gamma in TT or with a HTPC's video card - no? Does TSE's device affect the entire gamma curve or does it key in on the lower part only? Denon has some DVD players that allows one to adjust 10 points along the gamma curve for a very precise adjustment. Panasonic's solution I think is similar to a HTPC and effects the entire curve or most of it.

Don't some Barcos have gamma correction?

Gamma correction is a necessity for both CRTs and digital. IMO, since the gamma for CRTs is less than ideal to begin with and digital tries to emmulate CRTs gamma curve then digital is also out to lunch. Some digital projectors do offer some choice of gamma correction which is as step in the right direction.

A couple of questions for someone who might know - Can DVDs be encoded differently so that a fade to black would actually be a fade to black on a CRT and therefore we wouldn't have to resort to gamma correction to try to achieve TFTB while trying to avoid crushing blacks? Is gamma correction basically adjusting contrast in the bottom end of the video with less and less effect as you get into the midrange?
One last question - does increasing gamma put any additional strain on a CRT's tubes?

Cheers,

Grant
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post #114 of 492 Old 09-18-2005, 12:10 PM
 
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Quote:
Gamma correction is a necessity for both CRTs and digital. IMO, since the gamma for CRTs is less than ideal to begin with and digital tries to emmulate CRTs gamma curve then digital is also out to lunch. Some digital projectors do offer some choice of gamma correction which is as step in the right direction.
I do not necessarily agree with this assessment. Target gamma is for CRT, and I do not know what you mean when you say CRT gamma "is less than ideal." Usually, it is the digital projector's gamma that is incorrect in not matching the CRT gamma curve. Understand that when adjusting gamma on a CRT projector, you usually are moving *away* from the ideal curve, but it is because pushing the natural CRT gamma curve will obscure shadow detail because of ANSI washout.

The point isn't to adjust the gamma because the gamma is wrong, it is because ANSI is weak, we are making adjustments in gamma to compensate for low ANSI contrast, not because there is anything "wrong" with the gamma curve.

Quote:
Can DVDs be encoded differently so that a fade to black was actually a fade to black on a CRT so we wouldn't have to resort to gamma correction to try to achieve TFTB while trying to avoid crushing blacks?
This is something that has been discussed, and yes I think it's possible for full black scenes, but it gets more complicated with anything but full black. In any case I don't think it's really feasible as per standards, and in any case it is not occurring now.

Quote:
Is gamma correction basically adjusting contrast in the bottom end of the video with less and less effect as you get into the midrange?
A simple full-gamma adjust will affect everything obviously. You can try more advanced adjustments to more affect just the lower end, but something has to give somewhere to keep a continuous curve between black and white, so if you are increasing the slope from black for better contrast, somewhere that slope has to decrease. Spreading it out over the whole curve in a simple adjust is easiest, and it spreads out that decrease over the largest area.
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post #115 of 492 Old 09-18-2005, 06:14 PM
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Hi Benny,
So where is the schematic for the design.

Walter
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post #116 of 492 Old 09-18-2005, 06:40 PM - Thread Starter
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As no other projects were pending I spent some time playing with the response of the circuit today. The 120 ohm was changed to 75 ohm and the 430 ohm became a 510 ohm. That gave the first "step" in the 16 step stairstep pattern about 20% more amplitude than the original values. It is probably too much but the black bands at the top and bottom of my DVD image are zero light, none and the shadow detail is plenty. Between scenes the projector goes totally black.
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post #117 of 492 Old 09-18-2005, 10:09 PM
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I would be interested in a one of these if things work out and I have a neighbor that would like one as well.

Could someone summarize?-

Parts list is at the beginning of the thread (with some minor adjustments like that noted above).?.?.

Best place to go is 4pcb.com....or are others in this thread planning on coordinating a bulk order from somewhere for the pcb?.?.?

Are others looking at getting just the pcb or a complete pcb with all the parts soldered on?

Picree
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post #118 of 492 Old 09-19-2005, 07:23 AM
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Chris,

Thanks for the response.

Cheers,

Grant
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post #119 of 492 Old 09-19-2005, 05:30 PM
 
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If there is someone that could build one of these for me ? if so please let me know.I sold my soldering station awhile back and my hands are not as steady as the used to be.Getting older is a bitch but its better then the alternative :rolleyes: Anyways it is cheaper to buy more than one board and of course I would cover the cost plus time putting the board together.
I would love to try this with the MP modded Neo and Momitsu and the MP-5 :)
Just send me a PM.
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post #120 of 492 Old 09-20-2005, 09:22 AM
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Quote:
Originally Posted by PAW
I'd also like to see a few reviews of tse's and benny's mate's designs. Not that I don't trust either of you guys. I just value other opinions before I lay down my hard earned cash.

Russ - what's the input and output of your mate's design (RGBHV, component, VGA. etc.)? OK! I reviewed the thread from the beginning and found the test bench pics. Looks like input & outputs are BNC for RBG.
Completely understandably about having someone review it. When the final design is built up (soon) I'll be taking it to a few of the local CRT'ers for comments.

Connections will be 3 x BNC's IN and OUT and a socket for a powerpack to plug into. The Sync leads can remain undisturbed.


Quote:
Originally Posted by Deja Vu
Benny's diagram shows that his particular device affects the entire gamma curve, much like adjusting gamma in TT or with a HTPC's video card - no?
That is essentially correct Grant. Some more expansion of the very lower IRE levels has been incorporated also but not so much that it effects the overall dynamics of the image. This solution permits very fine adjustments of the curve, whereas the video drivers in the HTPC scenario generally have much coarser adjustments. At least the ATI's do .... I haven't had much exposure to the nVidia cards as yet.


Quote:
Originally Posted by WTS
Hi Benny,
So where is the schematic for the design.
Hi Walter ... my mate has chosen not to release the schematics at this moment in time.




The numbers my mate needs to run off a limited batch run for others are still a little short of the mark at the moment, so if you have a likely interest, pending suitable reviews of course, shot me a PM or say so here.

Cheers :)

Russ

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