CurtPalme.com Home Theater Forum

[kal]

Update: For a much better greyscale adjustment procedure, check out our GREYSCALE CALIBRATION FOR DUMMIES guide that anyone can use!

-----------------

In Jan 2006 I borrowed a Minolta CA100 CRT colour analyser to try and set D65 correctly on my Zenith PRO 1200x by adjusting the RGB gain and cutoff values. Here are my findings!


Minolta CA-100

Notes:

(1) If you've done your homework, you'll realize that the CA-100 was probably only intended to measure direct-view CRTs (not CRT projectors). Probably right, but I was still able to get an image that looks better then using nothing at all. So caveat emptor! Don't use something like a CA-100 if you expect perfection!

(2) Probe orientation plays a big factor in the x/y readings (most likely due to point (1) above). Move the probe slightly and the values change. To make my readings as consistent as possible, I placed the probe on a tripod in the center of the screen and rotated it up/down/left/right until the luminence value (Y) was as high as possible so that I knew it was pointing directly at the green tube. Better then no consistency at all I suppose (?).

(3) Please don't use my RGB gain/cutoff values and expect them to work the same way on your projector! They are only valid for my projector driven by my HTPC!

(4) I used the 10-100IRE window patterns from Avia to measure the xyY values off of the CA-100. These Avia window fields are known to contain some incorrect colour information , so I set my HTPC's saturation to zero (0) to stop from passing any incorrect colour information.

(5) The spreadsheet I used to do the calculations can be found here.



DEFAULT D65 SETTINGS

The idea here is to always display something that has no colour information when you go from black (0 IRE) to white (100 IRE). In other words, you want your display to never have any sort colour tint in it if you display varying levels of grey. Hence the reason this is called adjusting your 'greyscale'.

You use a colorimeter to measure three values: x, y, and Y. The only two we care about are x and y. We want to display various levels of grey from black to white and always try and get x to be 0.313, and y to be 0.329. Y is the total light output - really only useful to measuring how bright the projector is. You adjust the gains/cutoffs in your projector to adjust.

Most projectors that allow you to adjust the gains/cutoffs will usually have a default D65 setting (and possibly others). In my projector they are:

R: Gain=55, Cutoff=54
G: Gain=69, Cutoff=50
B: Gain=45, Cutoff=29

Usually these should take you pretty close to D65 if you were to map it out with a colorimeter, but that's not always the case.

I found this setting to be way too green in my setup. I plugged these values back in in order to map out the greyscale to see if my eyes were right. Here's what the CA-100 sees:



Yup. Too much green across the board. Not enough red in the mid and high ends, and not enough blue in the low and high ends.


'EYEBALLED' D65 SETTINGS

Since I don't have a colour analyzer myself, I 'tweaked' these values slightly a few months ago when I first set up my projector using this basic procedure. One of the first things I did was reduce the green gain, though I suppose I could have simply increased the two others to compensate. The end result was definitely better as there was less green, but it probably still wasn't very close to D65.

Here are my 'eyeballed' settings:
R: Gain=55, Cutoff=60
G: Gain=60, Cutoff=50
B: Gain=50, Cutoff=29

Here's what my 'eyeballed' settings actually look like to the CA-100:




The idea is to get x = 0.313, y = 0.329. Y is the total light output.

So green and red are now pretty much bang on, but there's way too much blue in the middle. I'm actually surprised how flat red and green are, but since you have to take all 3 colours together it's sort of meaningless.


CA-100 CALIBRATED D65 SETTINGS

So now I used the CA-100 to tweak the gain/cutoff settings to try and get flatter.

Here are my final settings:
R: Gain=54, Cutoff=59
G: Gain=60, Cutoff=50
B: Gain=39, Cutoff=35

Here's what my final settings look like to the CA-100:



I found it very difficult to get the projector to track correctly below 30IRE. If I set greyscale correctly at 20/80IRE the 30-40-50 range would be really off. So I ended up going between 30/70 to set up a good greyscale and left 20 'off' (as seen above). Someone more experienced with this sort of stuff could probably do better and flatten out the 10-30 range a bit better.

I ended up deciding to leave the green gain at 60 (instead of the default 69) since I like the amount of light output this gave me together with my contrast at 65. I could have reduced the contrast and left the green gain at 69 to give the same result. No difference I think.

There's still the typical (to CRT) blue hump in the middle but it's much better now.
The blue used to curve down at the end so I had to defocus blue electronically all the way down to the minimum value of 0 (it's sharpest at 41 for me). It's still slightly down at the high end but it's much better then if I left the blue electronic focus at 41. Blue focus is absolute crap now but you DO NOT notice this at all on screen, even with a 1-pixel wide white grid pattern from Nokia monitor tester.

My gamma curves still aren't right so I haven't posted them here. I'm still trying to figure out how exactly that's supposed to work. That'll be for a later time once I actually get my own colour analyzer and have more time to play with it.

Kal

[kal]

Update: For a much better greyscale adjustment procedure, check out our GREYSCALE CALIBRATION FOR DUMMIES guide that anyone can use!

-----------------

In Jan 2006 I borrowed a Minolta CA100 CRT colour analyser to try and set D65 correctly on my Zenith PRO 1200x by adjusting the RGB gain and cutoff values. Here are my findings!


Minolta CA-100

Notes:

(1) If you've done your homework, you'll realize that the CA-100 was probably only intended to measure direct-view CRTs (not CRT projectors). Probably right, but I was still able to get an image that looks better then using nothing at all. So caveat emptor! Don't use something like a CA-100 if you expect perfection!

(2) Probe orientation plays a big factor in the x/y readings (most likely due to point (1) above). Move the probe slightly and the values change. To make my readings as consistent as possible, I placed the probe on a tripod in the center of the screen and rotated it up/down/left/right until the luminence value (Y) was as high as possible so that I knew it was pointing directly at the green tube. Better then no consistency at all I suppose (?).

(3) Please don't use my RGB gain/cutoff values and expect them to work the same way on your projector! They are only valid for my projector driven by my HTPC!

(4) I used the 10-100IRE window patterns from Avia to measure the xyY values off of the CA-100. These Avia window fields are known to contain some incorrect colour information , so I set my HTPC's saturation to zero (0) to stop from passing any incorrect colour information.

(5) The spreadsheet I used to do the calculations can be found here.



DEFAULT D65 SETTINGS

The idea here is to always display something that has no colour information when you go from black (0 IRE) to white (100 IRE). In other words, you want your display to never have any sort colour tint in it if you display varying levels of grey. Hence the reason this is called adjusting your 'greyscale'.

You use a colorimeter to measure three values: x, y, and Y. The only two we care about are x and y. We want to display various levels of grey from black to white and always try and get x to be 0.313, and y to be 0.329. Y is the total light output - really only useful to measuring how bright the projector is. You adjust the gains/cutoffs in your projector to adjust.

Most projectors that allow you to adjust the gains/cutoffs will usually have a default D65 setting (and possibly others). In my projector they are:

R: Gain=55, Cutoff=54
G: Gain=69, Cutoff=50
B: Gain=45, Cutoff=29

Usually these should take you pretty close to D65 if you were to map it out with a colorimeter, but that's not always the case.

I found this setting to be way too green in my setup. I plugged these values back in in order to map out the greyscale to see if my eyes were right. Here's what the CA-100 sees:



Yup. Too much green across the board. Not enough red in the mid and high ends, and not enough blue in the low and high ends.


'EYEBALLED' D65 SETTINGS

Since I don't have a colour analyzer myself, I 'tweaked' these values slightly a few months ago when I first set up my projector using this basic procedure. One of the first things I did was reduce the green gain, though I suppose I could have simply increased the two others to compensate. The end result was definitely better as there was less green, but it probably still wasn't very close to D65.

Here are my 'eyeballed' settings:
R: Gain=55, Cutoff=60
G: Gain=60, Cutoff=50
B: Gain=50, Cutoff=29

Here's what my 'eyeballed' settings actually look like to the CA-100:




The idea is to get x = 0.313, y = 0.329. Y is the total light output.

So green and red are now pretty much bang on, but there's way too much blue in the middle. I'm actually surprised how flat red and green are, but since you have to take all 3 colours together it's sort of meaningless.


CA-100 CALIBRATED D65 SETTINGS

So now I used the CA-100 to tweak the gain/cutoff settings to try and get flatter.

Here are my final settings:
R: Gain=54, Cutoff=59
G: Gain=60, Cutoff=50
B: Gain=39, Cutoff=35

Here's what my final settings look like to the CA-100:



I found it very difficult to get the projector to track correctly below 30IRE. If I set greyscale correctly at 20/80IRE the 30-40-50 range would be really off. So I ended up going between 30/70 to set up a good greyscale and left 20 'off' (as seen above). Someone more experienced with this sort of stuff could probably do better and flatten out the 10-30 range a bit better.

I ended up deciding to leave the green gain at 60 (instead of the default 69) since I like the amount of light output this gave me together with my contrast at 65. I could have reduced the contrast and left the green gain at 69 to give the same result. No difference I think.

There's still the typical (to CRT) blue hump in the middle but it's much better now.
The blue used to curve down at the end so I had to defocus blue electronically all the way down to the minimum value of 0 (it's sharpest at 41 for me). It's still slightly down at the high end but it's much better then if I left the blue electronic focus at 41. Blue focus is absolute crap now but you DO NOT notice this at all on screen, even with a 1-pixel wide white grid pattern from Nokia monitor tester.

My gamma curves still aren't right so I haven't posted them here. I'm still trying to figure out how exactly that's supposed to work. That'll be for a later time once I actually get my own colour analyzer and have more time to play with it.

Kal

[Ridebreck]

Being a relative beginner in this hobby, this stuff is still rather space-age. Is there any sort of calculations that you do to determine how much to raise or lower gain and cutoff, or do you just keep adjusting and taking readings until you're satisfied?

Also, "gain"="g2" & "cutoff" = "drive", right?

[kal]

It's very much an interative process, where practice makes perfect. You use, say, 70IRE first and set your gains/cutoffs until you read 0.329. Then do the same at, say, 30IRE. Then you go back to 80IRE and see that everything's off so you re-tweak. Back and forth, back and forth....

When you eventually get something as close as you can at the two points, you track the whole range from 0-100 to see what it does and start the whole process over if needed.

Other things you can do:

- Defocus blue to get more blue output at the higher IRE's if needed to track better.
- Some PJ's (and scalers) have gamma adjustments or mid-point cutoff/boost adjustments that can help problem spots.

While different manufacturer's call Gain & Cutoff slightly different names, G2 is not gain.

Kal

[kal]

It's very much an interative process, where practice makes perfect. You use, say, 70IRE first and set your gains/cutoffs until you read 0.329. Then do the same at, say, 30IRE. Then you go back to 80IRE and see that everything's off so you re-tweak. Back and forth, back and forth....

When you eventually get something as close as you can at the two points, you track the whole range from 0-100 to see what it does and start the whole process over if needed.

Other things you can do:

- Defocus blue to get more blue output at the higher IRE's if needed to track better.
- Some PJ's (and scalers) have gamma adjustments or mid-point cutoff/boost adjustments that can help problem spots.

While different manufacturer's call Gain & Cutoff slightly different names, G2 is not gain.

Kal

[Ridebreck]

[kal]

Exactly!

And just like that procedure setting greyscale is as much an art as a science!

Kal

[kal]

Exactly!

And just like that procedure setting greyscale is as much an art as a science!

Kal

[stefuel]

I bought a Minolta a few months back and use it just as you suggest. It is a royal PIA to doc it. I put the probe on a tripod at the screen center pointing directly at the green. Set up the green and forget it. De-focus the blue a couple of clicks. Then set up the red and blue around the green at 30/70 IRE and it comes out real close. It put's out a real nice picture. There are those who will argue that this is not the way to do it. Perhaps, but it's gotta be better than "by eye". You obviously couldn't use one of these for a pro calibration device but for the hobbiest, it's just the ticket.

Question: How much does the blue have to "hump" in the middle for someone to look at your screen and be able to say "Hmmm, theres something wrong here"?

We know from years of everyone elses experiance that the blue needs to be defocussed to flatten out it's curve, so that's automatic for me. I can get dead balls D65 at 30/70 IRE. It it perfect? Probably not. Does it look good? Damn skippy it does

[kal]

[kal]

[stefuel]

[Z-Photo]

Thats funny-

a savy BB/CC shopper.... LMFAO

I always love to see the mits next to a sony next to a philips - what a frickin huge color shift.

[Mad Mr H]

BB ??

CC ??

Could you elaborate on those?

(UK Guy - guess you mean mutli brand shps but not sure)

[derfla]

Best BUY

Circuit city