CurtPalme.com Home Theater Forum

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

I measured my primaries & secondaries, and I'm a bit confused by what I see.

See the chart below. Magenta is nearly dead on, only off by 0.001 xy. Green is almost as good, off only 0.007. Red and blue are off a bit more (.025 & .012, respectively.)

What confuses me is yellow and cyan. If Green is almost perfect, and red is "too far out," then why is the yellow point off toward the green side? I would have expected yellow to be halfway between R & G. Would bringing the red in to its proper SMPTE C location bring yellow closer to red??

I assume you want the three dotted lines (between primaries & secondaries) to cross at D65. Mine don't, and I'm trying to decide what that means. Is the intersection point the place where the display **actually** displays 6500K white? If so, and if that intersection point isn't actually on the D65 point at 0.313/0.329, does that mean calibrating to .313/.329 puts you in the wrong place? Or does the colorimeter actually read .313/.329 at the point where the lines intersect, even if that isn't on the color-temp curve?

This probably won't change anything, since I can't fix the primaries or secondaries, but I'm curious...

**kal** · Posted: Thu May 01, 2008 12:43 am Post subject: Re: Primaries & secondaries

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

**kal** · Posted: Thu May 01, 2008 1:44 pm Post subject:

Gary,

You don't have greyscale readings in that file but I can get it from the "White" reading in the primaries/secondaries screen. Your greyscale isn't right. Your 100IRE white window x/y points are 0.307/0.355 instead of 0.313/0.329. That's a DeltaE of 23.4. Compare that to the my file: My 100IRE white window is at 0.311/0.336 which gives a DeltaE of 6.6.

To have accurate secondaries your greyscale has to be set correctly first *and* you have to have a display who's primaries are accurate too. So your blue/green levels aren't right which means that your secondaries will not be right either.

When displaying primaries (100% red, green, or blue) your other two tubes should be pretty much off - if they're not it's not that the cutoff isn't right but that the tube's G2 (or whatever it's called in Marquee's) isn't set right - not to be confused with the Marquee RGBLowEnd control which is actually called G2! (Confusing!). The real "G2" setting is a pot that controls at what point the tubes turn on/off.

But they'll never be completely off - you should still have the raster lit up just a bit even at 0 IRE. Try measuring your primaries with the other two tubes blocked with a piece of paper or something (or turn them off in the projector menus). I bet the primary readings will be pretty much the same a before. You'd have to have pretty screwed up G2s to mess up primary readings.

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

Gino · Posted: Fri May 02, 2008 4:33 am Post subject:

Kal, can you explain why 30%/80% is used? Rather than say 20%/80% or 30%/70%?

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

There's no particular magic about 30/80%. Some people try to use 10%/100% but that's not a good idea -- better to use something closer to 1/3 / 2/3 so you minimize the error across the IRE range. (Tune at 10%/100% and you might have a huge hump in the middle. Tune at 30/80 and the hump will shift down, being above in the midranges and below in the highest/lowest IREs, and the net error is less.)

**kal** · Posted: Fri May 02, 2008 2:45 pm Post subject:

What Gary said. 10IRE is also too low to reliably measure with most sensors, especially if your gamma is off (it'll be really dark).

Think of the RGB curves from 0 to 100 as sprint-loaded wires or something. If you hold them in place at 30 and 80 you sort of minimize your average error across the range. Do it only for the middle (50) and it'll likely bend down or swoop up at either end. Do it at 10 and 100 and the middle will bump up or down.

Kal

Gino · Posted: Sat May 03, 2008 5:57 am Post subject:

so using that logic, wouldn't 30/70 make more sense?

**kal** · Posted: Sun May 04, 2008 9:25 pm Post subject:

True. But 30/80 seems to be what everyone uses. Maybe the upper and lower range aren't 100% linear.

I've done it at 70 as well too. Doesn't really matter if you use 70 or 80. In the end you'll read the entire greyscale and tweak to try and even out any humps anyway.

Kal

VideoGrabber · Joined: 09 Apr 2006 Posts: 933 Location: Michigan

Gino,
> so using that logic, wouldn't 30/70 make more sense? <

Not really. You can't take a (meaningful) reading at 0, so the measurable/adjustable range is 10-100. 30-80 is +/-20 off that base. That's the logic anyway, but Kal's comments do apply.

**kal** · Posted: Mon May 05, 2008 3:04 pm Post subject:

Ha! Good point Tim. Never thought of that!

Kal

Gino · Posted: Tue May 06, 2008 5:05 am Post subject:

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

I did a more careful calibration on the full grayscale on my color-filtered Marquee. At first, after a touchup at 30%/80% but no blue defocus, I got a REALLY confusing display: my blue went UP at 90% and 100% !!? (First pic below.) I have NO idea what's up there.

So I defocused the blue a bit, and it looks much better. I still have a bit of a hump in the blue but not much, and I don't want to make the blue even fuzzier to fix that small hump. For the 8500 owners out there, my blue focus was at 47, though I think sharpest is actually about 50. I bumped it up to 59 for the final measurements.

DeltaE is 7.13 or below for 20-100%, color temp is 6374 at 100% but 6458-6668 for 20-90%. Gamma is actually a bit low (I have never gotten around to adjusting my Moome ext box) but I think I'll try it there for a while.

And now, with the grayscale correct, my secondaries are basically dead on. Smile

(The measurement dot waaay off to the left is IRE 0. That's way below what my colorimeter is capable of measuring, but I took the value it gave me. BTW these measurements were all done with my old Minolta TV2150, since the Spyder seems to be much less accurate. It's a pain to type in all the numbers but I think the result should be a lot better.)

Strangely enough, the final results show a bit of a hump in the RED. I didn't expect that. I've never heard of red overdriving the way blue does. I'm running the Marquee at 70 contrast (and still only getting 7.0 ftL off the screen, according to the Minolta!), but I don't think the red should be topping out. Anybody else seen humps in the red?

Gary

**kal** · Posted: Sun May 11, 2008 6:48 am Post subject:

Not bad at all Gary. Very nice. Similar to mine in that I can get everything from 20 to 100 nice but 10 IRE is off (no big deal).

Don't be afraid to defocus blue even more. If 50 is the sharpest and you're only at 47 that's nothing. For me, ~42 is the sharpest and I'm at 0. Yes, 0. If I put up a white crosshatch pattern you'll see blue halo's when standing up close to the screen but they're not visible at the seating position (12/13 feet back or more from my 8 foot wide screen).

Edit: That blue rise at 90 and 100 IRE in your first picture is very odd. Never seen anything like it. Weird!

Kal

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

No, sharp is at 50, I started out at 47, and I ended up at 59. 9 off is pretty significant for a Marquee. I haven't done a lot of viewing with it yet but I suspect the blue defocus might be noticeable at viewing distance on test patterns and credits.

I strongly suspect the wacky behavior at 0-10% is due to the colorimeter more than the projector. It reads 0.0 down there and the display flashes, indicating it's out of its range. (It's only rated down to 0.2 ftL.) 20% is 0.2 ftL so everything below that is questionable.

I've never been quite sure whether to believe the ftL measurements from this colorimeter. It says I'm only getting 7 ftL at 70 contrast, and I got similar readings with my XG and my G70. With just an 85" wide screen, I would expect more than 7 ftL even if it's slightly under 1.0 gain. Maybe if I ever get around to upgrading my screen I'll finally be able to get up to 9-10 ftL or so...

GEBrown · Joined: 08 Mar 2006 Posts: 729 Location: Denver

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

I have my Minolta sensor about 4" from the screen. My BOC probably has a gain of 0.9 or so. DW is 1.24, so the higher gain would only bump the reading up to 7.0*1.24/0.9 = 9.6 ftL.

I suspect the Minolta's ftL measurement is off. But could that be off if the color measurement is right (which it seems to be)? Seems unlikely, but...

Person99 · Joined: 09 Mar 2006 Posts: 4901 Location: Flower Mound, TX

Person99 · Joined: 09 Mar 2006 Posts: 4901 Location: Flower Mound, TX