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What creates CRT image depth?

 
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wanderer



Joined: 11 Jan 2015
Posts: 32



PostLink    Posted: Sat Nov 10, 2018 7:00 am    Post subject: What creates CRT image depth? Reply with quote


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I'm hoping to gain a better understanding on what factors go into making up CRT image depth. This is when you look at the screen and the image displayed has this deep depth of field to it, and it just draws you in. I got back into CRT about 2 years ago (thanks to Curt!) and this is the one thing I just haven't been able to nail down as to what defines this 'depth' effect.

My video chain is BD material > HTPC (Quadro) > VGA > Extron 203 > DTV-1200 > 100" Stewart Studiotek 130 G3. There is no sharpening on the HTPC side, nor any edge enhancements, etc, and the image looks very unprocessed, non sharpened and film like. I can mess around with the gamma at will and adjust that up or down as needed on the fly using madVR.

What I've been observing with my setup is:
1080p59 = Looks very detailed and film like. Some decent depth to the image.
810P59 = Not as detailed as 1080P for sure. Depth however in the image increases a bit.
720P59 = Not as detailed as 810P, and definitely less apparent detail than 1080P. Depth however just takes off and goes deeeep into the background.

BD Movies look really impressive at 1080P and I'm always wowed by this. I take that exact same movie and output at 720P and now it becomes deeply engaging with the added image depth. Scary movies go from 'it's scary' to really disturbing. Jurassic Park looks stunning with all the added depth. You go back to 1080P for a back to back comparison and that looks more detailed but considerably flatter in depth by comparison.

Originally I thought this was bandwidth related. Then I thought maybe it was nyquist due to the filtering effect of the quality downscale. Then I thought ANSI and maybe better rise\fall times on the scan line as it went across. But I'm lost, I just don't get it and I can't work it out. Clearly there is some science magic going on here so I'm hoping someone can jump in and explain it to me!
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gjaky



Joined: 05 Jun 2010
Posts: 2570
Location: Budapest, Hungary


PostLink    Posted: Sat Nov 10, 2018 10:56 am    Post subject: Re: What creates CRT image depth? Reply with quote

wanderer wrote:

Originally I thought this was bandwidth related. Then I thought maybe it was nyquist due to the filtering effect of the quality downscale. Then I thought ANSI and maybe better rise\fall times on the scan line as it went across.


FYI rise/fall times are very closely related to video bandwidth, so this is a very valid point also in my opinion.
Also, CRT is hands down the best when it comes to produce a blurred image as it is usualy needed on backrounds, because of the inherent round shape of the electron beam (an very simliar to human sight). Although this happens at the expense of a blurry foreground. Decent bandwidth can help on this to some extent.
A digital display, regardless of resolution is sharp because of the square shaped pixels, they have/had problem producing blurry images instead, both because of the edgy pixels and the fact pixels need space inbetween making the edgy pixels more apparent. This is however got better with increasing the pixel density of the digital displays. Although as it seems digital displays often use some image enhancement algorithms (eg. added sharpness) that adversely affect the smooth background, but foreground will be razor sharp.
In the end it all boils down to personal preferences (or marketing hypes).

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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
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kal
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Joined: 06 Mar 2006
Posts: 15478
Location: Ottawa, Canada

TV/Projector: JVC DLA-RS56


PostLink    Posted: Sat Nov 10, 2018 3:09 pm    Post subject: Re: What creates CRT image depth? Reply with quote

Contrast ratio. Once you get to a certain contrast ratio the image has depth.

wanderer wrote:
BD Movies look really impressive at 1080P and I'm always wowed by this. I take that exact same movie and output at 720P and now it becomes deeply engaging with the added image depth.

I'm assuming this is on your CRT. That's because at 1080p the projector is working harder. The signal beam doesn't have enough time to turn on and off as well as when running at slower 720p. Your ANSI contrast ratio difference is likely the cause. At 1080p things painted on screen are closer to each other in terms of brightness. The beam doesn't have as much time to turn off to paint the blacks as well or enough time to turn on as bright for a bright spot.

For what it's worth, I get just as much image depth if not more from my current JVC RS56 digital as I did from my Barco Cine8 Onyx (clone) CRT projector. Both have (or had) great contrast ratio.

Kal

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gjaky



Joined: 05 Jun 2010
Posts: 2570
Location: Budapest, Hungary


PostLink    Posted: Sat Nov 10, 2018 3:25 pm    Post subject: Re: What creates CRT image depth? Reply with quote

kal wrote:
Contrast ratio. Once you get to a certain contrast ratio the image has depth.

wanderer wrote:
BD Movies look really impressive at 1080P and I'm always wowed by this. I take that exact same movie and output at 720P and now it becomes deeply engaging with the added image depth.

I'm assuming this is on your CRT. That's because at 1080p the projector is working harder. The signal beam doesn't have enough time to turn on and off as well as when running at slower 720p. Your ANSI contrast ratio difference is likely the cause. At 1080p things painted on screen are closer to each other in terms of brightness. The beam doesn't have as much time to turn off to paint the blacks as well or enough time to turn on as bright for a bright spot.

For what it's worth, I get just as much image depth if not more from my current JVC RS56 digital as I did from my Barco Cine8 Onyx (clone) CRT projector. Both have (or had) great contrast ratio.

Kal


What you wrote better suits to the term MTF.
Ansi contrast is measured by means of a checkboard test pattern, Id be really surprised to see ANSI contrast depending of the output resolution on any device.

_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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wanderer



Joined: 11 Jan 2015
Posts: 32



PostLink    Posted: Thu Nov 15, 2018 4:31 am    Post subject: Re: What creates CRT image depth? Reply with quote

gjaky wrote:
wanderer wrote:

Originally I thought this was bandwidth related. Then I thought maybe it was nyquist due to the filtering effect of the quality downscale. Then I thought ANSI and maybe better rise\fall times on the scan line as it went across.


FYI rise/fall times are very closely related to video bandwidth, so this is a very valid point also in my opinion.
Also, CRT is hands down the best when it comes to produce a blurred image as it is usualy needed on backrounds, because of the inherent round shape of the electron beam (an very simliar to human sight). Although this happens at the expense of a blurry foreground. Decent bandwidth can help on this to some extent.
A digital display, regardless of resolution is sharp because of the square shaped pixels, they have/had problem producing blurry images instead, both because of the edgy pixels and the fact pixels need space inbetween making the edgy pixels more apparent. This is however got better with increasing the pixel density of the digital displays. Although as it seems digital displays often use some image enhancement algorithms (eg. added sharpness) that adversely affect the smooth background, but foreground will be razor sharp.
In the end it all boils down to personal preferences (or marketing hypes).


The 720P image is around 74Mhz in bandwidth, so it's being pretty nice on the projector. The easier rise\fall times might be a factor as it allows a rendering of the image that just seems to have the right depth queues to it. An example is an image where you look at points A and B in an image and you say to yourself that there should be say 20ft in apparent image depth\distance between those 2 points. And with this bandwidth on this video chain, that's what it looks like. The brain just seems to put it together and it's pretty amazing.

Throw at 1080P image (~180Mhz) and it's flatter without the added depth. That 20ft of apparent depth from A > B points might now look like only a few feet. This could be due to the blurry foreground\blurry background effect where it's just not as precise at 180Mhz due to the bandwidth. And the image depth suffers as a result.

This is all a subjective evaluation here on my part. There is no test pattern or image that I'm aware of that tracks this effect at all.
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wanderer



Joined: 11 Jan 2015
Posts: 32



PostLink    Posted: Thu Nov 15, 2018 5:59 am    Post subject: Re: What creates CRT image depth? Reply with quote

kal wrote:
Contrast ratio. Once you get to a certain contrast ratio the image has depth.

wanderer wrote:
BD Movies look really impressive at 1080P and I'm always wowed by this. I take that exact same movie and output at 720P and now it becomes deeply engaging with the added image depth.

I'm assuming this is on your CRT. That's because at 1080p the projector is working harder. The signal beam doesn't have enough time to turn on and off as well as when running at slower 720p. Your ANSI contrast ratio difference is likely the cause. At 1080p things painted on screen are closer to each other in terms of brightness. The beam doesn't have as much time to turn off to paint the blacks as well or enough time to turn on as bright for a bright spot.

For what it's worth, I get just as much image depth if not more from my current JVC RS56 digital as I did from my Barco Cine8 Onyx (clone) CRT projector. Both have (or had) great contrast ratio.

Kal

On this stock projector, it's possible a 720P image throws a more properly resolved image 'depth' wise than what it does when the bandwidth goes up for the 1080P image. You'd never know unless you did a back to back comparison.

Strangely enough, I know the JVC black levels pretty well as i've had one here. I actually went through 2 x RS40 models very early in their run but both went back as defective due to poor factory QA. This was before the lamps blowing up episodes. The black levels were great though for sure from those projectors.
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spankedmonkey



Joined: 03 Feb 2011
Posts: 17



PostLink    Posted: Tue Nov 20, 2018 6:26 pm    Post subject: Reply with quote

So would it be your preference to view at 720p? Also given that youre running a DTV-1200 I would be curious as to how does depth at 1080p translate on other 9 models (G90, 909, Cine-9, Marquee 9500)? Im running a G70 VR lenses at 720p, but looking someday to go up to a 909 or Cine-9.
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kal
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Joined: 06 Mar 2006
Posts: 15478
Location: Ottawa, Canada

TV/Projector: JVC DLA-RS56


PostLink    Posted: Tue Nov 20, 2018 6:44 pm    Post subject: Reply with quote

I used to use 1080i instead of 720p myself. That way I wasn't giving up any of the 1920x1080 resolution.

Kal

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wanderer



Joined: 11 Jan 2015
Posts: 32



PostLink    Posted: Wed Nov 21, 2018 12:38 am    Post subject: Reply with quote

spankedmonkey wrote:
So would it be your preference to view at 720p? Also given that youre running a DTV-1200 I would be curious as to how does depth at 1080p translate on other 9 models (G90, 909, Cine-9, Marquee 9500)? Im running a G70 VR lenses at 720p, but looking someday to go up to a 909 or Cine-9.

Good question. If I valued resolution and more apparent visible detail then hands down, it would be 1080p. If I valued deep 2D depth in the image it would be 720P. Which image drags me more into the movie and image? It's definitely 720p.

This could be my setup. My VGA chain puts out a very clean looking signal and I always have peaking off in the projector as well. The Quadro card in question is specified for use in high resolution medical imaging and runs a factory firmware which also has all the Nvidia audio functions disabled. Would you get the same deep 2D depth effect doing HDMI digital > moome card > projector? I don't know as I don't have that chain.

The DTV-1200 (Cine-9) throws pretty much an identical image as a 909 if you have the same colored C elements installed.
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wanderer



Joined: 11 Jan 2015
Posts: 32



PostLink    Posted: Wed Nov 21, 2018 12:50 am    Post subject: Reply with quote

kal wrote:
I used to use 1080i instead of 720p myself. That way I wasn't giving up any of the 1920x1080 resolution.

Kal

In chasing down the video bandwidth angle, I did try 1080i as well to try and get the 2D depth and the 1080 resolution. Video chain on this was through a TVone C2-1250 and later a C2-2200, outputing 1080i60, 1080i72 and 1080i96. I discovered a few things: 1080i on a 9" looked awful with any left\right movement as the scan lines were highly visible and distracting, and that the deep 2D depth effect just wasn't there despite having similar bandwidth to my 720p signal. The Quadro card can't do any interlaced output so I couldn't run the test from there.
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km987654



Joined: 25 Jul 2007
Posts: 2730
Location: Australia

TV/Projector: Barco BG809s


PostLink    Posted: Wed Nov 21, 2018 3:32 am    Post subject: Reply with quote

wanderer wrote:
kal wrote:
I used to use 1080i instead of 720p myself. That way I wasn't giving up any of the 1920x1080 resolution.

Kal

In chasing down the video bandwidth angle, I did try 1080i as well to try and get the 2D depth and the 1080 resolution. Video chain on this was through a TVone C2-1250 and later a C2-2200, outputing 1080i60, 1080i72 and 1080i96. I discovered a few things: 1080i on a 9" looked awful with any left\right movement as the scan lines were highly visible and distracting, and that the deep 2D depth effect just wasn't there despite having similar bandwidth to my 720p signal. The Quadro card can't do any interlaced output so I couldn't run the test from there.


Not sure about your projector but I am running 1080i/96 and it looks far better than 720p. There is no problem with movement you can even look into the lens and see smooth movement. You have too look really closely to see any scan lines. Anything less than 96HZ can show movement and scan lines. I run a C2-7100. Input to the C2-7100 is 1080p/24.
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gjaky



Joined: 05 Jun 2010
Posts: 2570
Location: Budapest, Hungary


PostLink    Posted: Wed Nov 21, 2018 8:20 am    Post subject: Reply with quote

If we suspect bandwidth, then there would be an easy way to test it. Stick with one resolution, 720P would be perfect for now. Increase the refresh rate, hence the bandwidth, 720P 144Hz has more bandwidth than 1080P 60Hz, so would be nice to compare 720P 72Hz to 720P 144Hz for image depth.
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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spankedmonkey



Joined: 03 Feb 2011
Posts: 17



PostLink    Posted: Wed Nov 21, 2018 11:04 pm    Post subject: Reply with quote

So does this mean that the 9 models have issues resolving 1080p while retaining the virtues of CRT (contrast, deep colors, 2D image depth, motion retention)? Does shortcomings occur when the chain of source increases, or not so much so when source to pj is achieved by simplest path? Im really aiming for a 9er but hope that it would be able to get that through-the-looking glass, texture resolving image of 1080p. In any achievable resolution/bandwidth within capability.
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wanderer



Joined: 11 Jan 2015
Posts: 32



PostLink    Posted: Wed Nov 21, 2018 11:28 pm    Post subject: Reply with quote

gjaky wrote:
If we suspect bandwidth, then there would be an easy way to test it. Stick with one resolution, 720P would be perfect for now. Increase the refresh rate, hence the bandwidth, 720P 144Hz has more bandwidth than 1080P 60Hz, so would be nice to compare 720P 72Hz to 720P 144Hz for image depth.

This is an excellent idea! I am going to do this as it should definitively answer the bandwidth question I have. It may take me a week or so though for the results as the PJ is down for a new mounting system I am setting up.
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wanderer



Joined: 11 Jan 2015
Posts: 32



PostLink    Posted: Wed Nov 21, 2018 11:34 pm    Post subject: Reply with quote

km987654 wrote:
Not sure about your projector but I am running 1080i/96 and it looks far better than 720p. There is no problem with movement you can even look into the lens and see smooth movement. You have too look really closely to see any scan lines. Anything less than 96HZ can show movement and scan lines. I run a C2-7100. Input to the C2-7100 is 1080p/24.

Is this looks better with more 2D image depth, or looks better in more apparent image resolution?
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wanderer



Joined: 11 Jan 2015
Posts: 32



PostLink    Posted: Thu Nov 22, 2018 12:12 am    Post subject: Reply with quote

spankedmonkey wrote:
So does this mean that the 9 models have issues resolving 1080p while retaining the virtues of CRT (contrast, deep colors, 2D image depth, motion retention)? Does shortcomings occur when the chain of source increases, or not so much so when source to pj is achieved by simplest path? Im really aiming for a 9er but hope that it would be able to get that through-the-looking glass, texture resolving image of 1080p. In any achievable resolution/bandwidth within capability.

With a 9"er I think you can definitely get that through the looking glass effect you are looking for. The contrast, deep colors, 2D depth and motion retention are all there and this is probably the best implementation of CRT there ever was. These are all major factors why I came back to CRT after years in the digital world.

'Resolving' 1080p though is another thing, and I'm not going to dive into that although I'm sure others will put their thoughts out there. I have a Runco DLP LED pj here with a sharp lens, and that thing absolutely can resolve 1080p. It's plenty bright, it's plenty sharp and the image just screams digital to me. I feel like I'm literally watching pixels with this thing. So if this DLP pj resolves 1080p cleanly, what does that mean for the CRT image with the same source?

For me, I've come to a conclusion that I'm not really concerned with resolution anymore; I am more concerned with how the image looks and how involving it is to watch. I like looking out the window at real life and seeing the color of the sky, clouds, trees, image depth, etc. I want that same effect in my display and if it means running at a higher or lower resolution to maximize the image, I'm totally OK with that. That's kind of why I started this thread, to try and drill down and better understand what gives that 2D depth to the image.

I wish we had some test patterns or images that could measure this 2D effect, but there are none that I'm aware of. I have found some film material and scenes which seem to draw this effect out, but I will have to dive into that some more once my CRT is back up on the ceiling.
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km987654



Joined: 25 Jul 2007
Posts: 2730
Location: Australia

TV/Projector: Barco BG809s


PostLink    Posted: Thu Nov 22, 2018 7:48 am    Post subject: Reply with quote

wanderer wrote:
km987654 wrote:
Not sure about your projector but I am running 1080i/96 and it looks far better than 720p. There is no problem with movement you can even look into the lens and see smooth movement. You have too look really closely to see any scan lines. Anything less than 96HZ can show movement and scan lines. I run a C2-7100. Input to the C2-7100 is 1080p/24.

Is this looks better with more 2D image depth, or looks better in more apparent image resolution?


Both. Its just shows cleaner lines better contrast and more detail. Of course ever projector is different. I have replaced CAPs on a number of boards and this does make a big difference so this to some degree will make it difficult to compare but I would say if you are really interested in a great picture you might consider replacing 20 year old CAPs.
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