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Discussion Starter · #1 ·
Is there a such thing?


I'd like to see a comparison of my 17 year old Kmart-aquired 27" Sharp TV compared to the IF 4805 projector in terms of resolution vs viewing distance...


I know my Projector has better resolution (ED) but I'm wondering how the PQ will compare to my old CRT once I blow up the picture (thinking 72" wide x 40.5 tall, 16:9)... Planning to sit 11.5 feet from the screen. If I calculated right this will be a 1.9 viewing ratio. My CRT sits 2 feet closer to my face but still gives a healthy 5.3 viewing ratio (21.6" wide). VR = eye distance to screen / screen width, right?


Ok... Also... I know that guys with HD-capable PJs and TVs will obviously get a better picture than me but at what point will I get an equivalent resolution to them if I shrink my image...? For instance, if they have a 100 wide screen (in 16:9 format), how much smaller does my screen have to be to be equivalent to theirs if I'm sitting 2X the width of my screen?


Seem like this would be the best way to measure one's true need for an HD signal. Can anyone help me?
 

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Quote:
Originally posted by Cavemanhead
Is there a such thing?


I'd like to see a comparison of my 17 year old Kmart-aquired 27" Sharp TV compared to the IF 4805 projector in terms of resolution vs viewing distance...


I know my Projector has better resolution (ED) but I'm wondering how the PQ will compare to my old CRT once I blow up the picture (thinking 72" wide x 40.5 tall, 16:9)... Planning to sit 11.5 feet from the screen. If I calculated right this will be a 1.9 viewing ratio. My CRT sits 2 feet closer to my face but still gives a healthy 5.3 viewing ratio (21.6" wide). VR = eye distance to screen / screen width, right?


Ok... Also... I know that guys with HD-capable PJs and TVs will obviously get a better picture than me but at what point will I get an equivalent resolution to them if I shrink my image...? For instance, if they have a 100 wide screen (in 16:9 format), how much smaller does my screen have to be to be equivalent to theirs if I'm sitting 2X the width of my screen?


Seem like this would be the best way to measure one's true need for an HD signal. Can anyone help me?
I'm not positive but I don't think many of your questions make sense. Shrinking an image doesn't provide better resolution. If you projector is set to native then that's as good as it gets. Blowing the picture up is a scaling issue. For example, I have a 800X600 projector that fills a 120 inch screen when sent a full 800X600 resolution from a computer. If I just play a regular DVD and get 720X480 then obviously the picture doesn't fill the full screen unless I have the projector scale it up to 800X600.


Making the image smaller with the zoom lens might make the picture look better but that's not a resolution thing, it's more a lumens thing I believe since you can focus the light more.
 

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Discussion Starter · #4 ·
I'm coming at it from the perspective of someone who understands computer monitor resolutions... Perhaps this is not a correct understanding? Assuming it is similar:


A 20 inch monitor (image) looks horrible with 800 x 600 resolution. Now, take that same image and display it on a 14" screen and violla, the picture is crystal clear becasue each pixel is smaller and your eye can't resolve each pixel as easily thus blending the image. I'd assume projectors are similar though I'm not sure. Can someone make the water less murky here?


Thanks.
 

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It's called viewing angle.


It comes into play quite a bit as to what resolutions and pixel density supports how close a viewing angle.


This is best discussed in terms of x distance away in terms of screen width.
 

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Discussion Starter · #6 ·
I tried the glossary and there's nothing there that says anything about viewing angle... Can anyone give me some idea about the answers to my questions?


If it's the width of the screen that defines VA, it seems it would vary depending on the aspect ration you have 4:3, 16:9, etc...


Also, another term that I can't figure out is "hotspotting". Not in the glassary either... Seen it used lots but never defined...


Also...
 

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with viewing angle the width stays the same pretty much. That's why the width is convenient.


hotspotting is due to a high-gain screen being too bright in the middle due to it being very directional.
 

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I think what you're asking is this: What is the subtended angle covered by a display pixel given a certain screen size, display resolution, and viewing distance? The larger the angle that the pixel covers, the larger it appears.


Before I show the trig, it must be explained that since we use flat screens, the subtended angle is actually different for each pixel depending on how far away it is from the perpindicular line traced from your eye to the screen. The farther away from the center of the screen you go the smaller the angles become (think of looking at a picket fence that extends very far to each side, and how the slats look like they get closer and closer together the farther out to the side they are). For this reason it is easiest to just use the subtended angle for the pixel directly in front of you, right on that line that runs perpindicular from the screen to your eye.


Here is the simple trig calculation (remember to use the same units for length, like inches)


---

PH = pixel height

PA = pixel angle

SH = screen height

VD = viewing distance

VR = vertical resolution (# of pixels from top to bottom of screen)

---

PH = SH / VR

PA = 2* atan [(PH/2) / VD]


(This should come out the same if you use screen width and horizontal resolution too, since the pixels are square)


PA should give a useful metric for comparing different screen sizes, different resolutions, and different viewing angles, given all else is equal (signal quality, optics quality, processing quality). The smaller the angle, the harder it is for our visual system to make it out as a discrete "pixel", and the more the pixel array appears as a continuous image. (Flame suit: I know it is much more complicated than this, but I'm trying to distill it down to the basics here)


One caveat is that the source material resolution matters too. For example, even though my pj has 720 lines, DVDs only contain 480 lines of information and therefore it would be more accurate (although not entirely accurate) to use 480 for VR in the above equation instead of 720. For 720p HDTV material I could use the 720 lines, however.
 

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For CRTs and other fixed panel displays, you are referring to pixel pitch or something like that (akin to DPI in the world of printers etc.)


I don't think a calculator will do much good however when comparing different display technologies. There are just too many other factors at play to try, a simple demonstration will work wonders.


Cheers...

Duy-Khang Hoang
 
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