CurtPalme.com Home Theater Forum

panzeroceania · Joined: 23 Sep 2011 Posts: 24 Location: Salem, Oregon

Recently I was wondering how the boards inside a CRT handle color gamut, and what the standards and limitations are.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

The colors of the CRTs themselves determine the ultimate extension of their color gamut.

Most better units are equipped with color corrected (filtered) red and green CRTs which achieve rec. 709 (HD) color coordinates,
or come so close as not to matter.

Without color filtering, the red has too much yellow in it and the green also has too much yellow in it.

These days, it is rare for a person who uses a CRT projector to be using an input that makes use of the projector's internal color
decoder, which would be applicable to composite and S-video signals. We use either the direct RGBHV inputs or use DVI or HDMI input cards, or an external device that derives RGBHV from the source and sends it to the projector as RGBHV. (Not common these days. Most serious CRT enthusiasts have the HDMI input cards or a device that serves the same purpose.)

There really is no on-board color processing going on, other than gamma correction, inside the projector when using the RGB inputs, or HDMI or DVI inputs. Or even component inputs, which will be processed at the component input card.

panzeroceania · Joined: 23 Sep 2011 Posts: 24 Location: Salem, Oregon

thanks for the reply! The reason I ask is there was someone on another forum talking about colors on a monitor that show in NTSC not showing up over RGB.

NTSC is a large color gamut, and larger than sRGB/Rec709 to be sure, but these monitors aren't limited by those gamuts.

are you saying that say, a Sony BVM-20F1U, or Sony G90 wouldn't be able to reach the edges of say NTSC, DCI-P3, AdobeRGB, color space? That they might not even be able to reach sRGB/Rec709 over their RGBs/RGBHV inputs?

I would have assumed they could surpass the sRGB/Rec709 color space as it's not that large.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Read my comments again. Our CRT projectors (most of them) were designed from the start to be able to achieve rec. 709 color coordinates even if it requires color corrected C elements.

A well calibrated CRT projector should be able to be calibrated to rec. 709.

The color correction is only to remove excess yellow from the output of the red and green projection phosphors.

Your statement of NTSC being a large color gamut, larger than rec. 709 and sRGB, is, according to all the data I have gathered,
false. And WHICH NTSC standard are you referring to? The color gamut standards changed froim time to time. And they
were established, and limited, by the properties of the color phosphors available at the time they were established.

The HD color specifications were established around 1990, which was prior to the design of most of the CRT projectors in common use in the years following. You may assume that any CRT projector type that was designed by the mid 1990s was built to handle the rec. 709 colorspace.

The NTSC color gamut specification was initially established in 1931 with the CIE 1931 specifications and was revised in 1953 and again in 1976 via the CIE 1953 and CIE 1976 revisions.

The difference between rec. 601 (CIE 1976) and rec. 709 (HD) is not large. But 709 is a wider gamut.
Rec. 2020 is considerably larger and beyond the capacity of the phosphors of our CRTs to deliver.

Development of new CRTs with UHD spec phosphors, while technically possible, is rather unlikely unless a well heeled CRT enthusiast were to agree to support the developmental costs and also commit to the purchase of probably not less than 100 sets of UHD colorspace spec CRTs. Probably they would incorporate quantum dot phosphor technology, which would give several
theoretical advantages over conventional phosphors.

If I win a large lottery and have a few million extra dollars burning a hole in my pocket, I'll fund this.

panzeroceania · Joined: 23 Sep 2011 Posts: 24 Location: Salem, Oregon

I was referring to CIE 1976, and I see I had several false assumptions. Looking at then as far as gamut, looks like they are more or less equal with some fringe colors in each of them that aren't found in the other, but they're pretty minor

So I suppose it is always CIE 1953 that people are comparing to AbobeRGB as covering roughly the same colors, as seen here

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

See http://www.curtpalme.com/forum/viewtopic.php?t=5604 for a study I did on my 8500. You can see the color coords of the uncorrected phosphors, with experimental Calcolor gels, and with color-corrected HD-145 lenses. It doesn't look like the corrected lenses move things that much, but it makes a big difference in the colors you see on the screen.

panzeroceania · Joined: 23 Sep 2011 Posts: 24 Location: Salem, Oregon

That was sort of my next question, has someone measured something like a Sony G90 with a colorimeter, and where does it fall on these charts.

And what is SMPTE-240M, and CIE RGB?

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

Yes, but I don't know if any posted any results. I don't see any in a quick search.

panzeroceania · Joined: 23 Sep 2011 Posts: 24 Location: Salem, Oregon

but based on what I've seen here, it should fall close to SMPTE-C (1994) / Rec709 / sRGB ?

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

Yes, I'm sure it does. Maybe one of our Sony experts can confirm.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

The G90's native (CRT) colorimetry will be the same as any other projector that uses the same tubes and phosphors,
with the caveat that the G90 comes stock with a very lightly tinted green C element which is there to provide SOME color correction
but permit higher on-screen brightness than if using a "standard" tint green C element.

Any projector that uses Panasonic type CRTs will be using the same phosphors which output the same colors.

The color gamut of a G90 is identical to that of a Barco or Electrohome or AmPro CRT projector because the phosphor colors are the same. C elements are the only option/variable that will materially change this.

**kal** · Posted: Wed Feb 15, 2017 12:25 am Post subject:

panzeroceania · Joined: 23 Sep 2011 Posts: 24 Location: Salem, Oregon

Thanks guys, you've been very helpful and informative.

cmjohnson, even if we had the money for new CRT development, who would you approach to get it done?

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Lexel, Mikado, or Thomas, the three remaining projection CRT manufacturers.

Spanky Ham · Joined: 22 Mar 2006 Posts: 5643 Location: Comedy Central

While 709 can be achieved by CRT, it is doubtful that CRTs will be able to handle the new color spaces.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

They WON'T unless new CRTs are made with new phosphors that achieve the required color coordinates. Which is unlikely unless some rich enthusiast wants to bear the expense of development.

You can't go deeper into the color gamut than the phosphor emission allows. No getting around that.