HD1080i De-mystify HDTV 1080i ::: know why before you buy

Saturday, January 20, 2007

Size Matters: Resolution vs distance

HOW BIG IS YOUR PIXEL?
This Chart has distance vs screen size for various resolutions, with lines drawn indicating THX and SMPTE guidelines, typical of Home Theater setup documents, this one was compiled by another bloggin enthusiast, Carlton.



click to enlarge

click to enlarge.

According to this graph, these standards for a 55" display at 1080 are around 8 feet distance. For me anyhow, that is pretty close, but its easy to see this graph plots distance to equal visual quality, and represents the avg distance to resolve 2pixels visually at the same size. Meaning: resolution and pixel size matter when you take any given image and spread it out over a screen area.

I know you are looking at your computer screen , so try this gray/grid test:



Its sort of an eye test, 2 x 2 pixel boxes in gray , surrounded by 1 pixel wide black lines, solid gray to the right.

TAKE A TEST:
Assuming a typical 1024 x 768 laptop 15 to 17" display is in front of you,
look at the grid and move back until it looks all basically gray.
Measure (or guess) your distance.
Using the chart above, follow the red 1080p line.
A good size for you may well be the screen size in the x axis.

Typically if it takes 8-10 feet before you see all gray in the left box, then you will definitely see value in the accuracy of owning a 1080 resolution display, in a typical living space , at 50-60" in size. Of course, that isnt scientific or statistical in any way, but it does help you think about the value of detail with respect to your eyesight.

This means seeing a single pixel, and easily resolving 2 pixels which is the width of the text in white. On Displays that "Scale" you can slide the browser and see the pattern in the grid is banded and fixed to a screen position.

For our purposes we are discussing HD that is flatpanel Pixel-for-Pixel accurate or a fixed pixel display.

Edit Desk:

3 LG Flatrons 1680 x 1050 and one 37" Westy digital 1080p. This is one place where up close like 4 feet distance reveals all in the HD display. Great for editing HD video and checking compression artifacts in the final render of a project. In some ways, compression matters more than display resolution when visible compression artifacts exist. CBR ( Constant Bit-Rate Mpeg ) is probably the worst culprit. Depending on the scheme used, you may see square or vertically rectangular blocks in high action scenes and scene cut recovery.

Most people dont want to see blocks on the video with a pixelly feel, but often, thats what you get in a 1080i broadcast that is over compressed, and in that case 1080 display shows about the same picture as a 1366, its called:

Broadcast compression blocking: MACROBLOCK.
This stuff is blatant and visible is usually much greater than 2 pixels, typical is more like 16 x 16 pixels in MPEG 2. High action scene cuts like this explosion in STAR WARS broadcast:


Kind of a blocky moment above. This isnt Native resolution fat pixels, its compression artifacts that create a loss of detail during high action event moments, a bandwidth issue for constant bitrate mpeg. Dont allow yourself to view such stuff when buying. Ask for a Blu-ray source to see on the display, perhaps a KING KONG scene, and play it at full frame and slo-mo speed.

1080 LCD accuracy is undeniably rigorous and in my humble opinion, broadcast 1080i mpeg transport stream compression doesnt often live up to the ability of a good 1080p display, yet anyhow. For dramatic high action kept clean, like most of the well crafted HD movies, you most definitely want your 1080 to be from a Blu-ray or HD-DVD. It's just the way it is, and this is what THX is really telling you, for HD off a disc, sit close for home theater experience...but...

So how big is your Pixel?
If you sit close enough to the display to see a single pixel then it would seem you are close enough for sure, the rest depends on eyesight for a lot, one thing that HD does for you is let you see detail textures of a surface that in 480i would just be a solid blotch, the incredible set design detail of many Sci-Fi movies with scenes depicting size and scale that the director used for a purpose. Accurate resolution also give you much more of a connected presence, like being right there in the scene, reading what is on all the signs in Times Square for the King Kong movie for me was a real treat.

FIXED PIXEL DISPLAY is the basis of flatpanel tech.
In the early days of CRT Tubes they used to market pixel size at DOT PITCH, in millimeters, so a .28mm dot pitch meant a nice tight pixel on the screen. Mots people didnt know what that meant but understood a smaller number meant a nicer screen. Sort of like Jessica saying "I totally dont know what that means, but i want it". These days dot pitch or the physical pixel size is not marketed or even in the Spec Sheets. I think it should be.

Pixel Shape
Most people looking at standard TV dont realize the pixel they see is not square but in fact a rectangle. Most Plasma screens and LCD is square pixel, but 4:3 NTSC TV is a .9091 to 1 shape. Not square. So when you see a regular pillar boxed STD def TV show on your HD screen, its really scaled in a lot of ways.

Back in early TV for Color on CRTs they worked it out by placing Red, Gren, Blue vertically masked bars or color subpixels with very thin black borders separating the colors for the electron gun to scan. This caused a need to "converge" in STD TV sets ( get Red Green and Blue to line up ) . We got used to fuzzy in the process, tint knobs, yuch. HD TV is not fuzzy now and square uniform pixels are part of that.

HD PLASMA 1366x768 runs into the same problem that regular TV CRT masks had, in much larger PLASMA screens the black area surrounding each pixel of Red Gren and Blue dots can be visible. They call this the "Screen Door" effect, since up close, your picture looks like you are seeing it through screening, which in a way, you are... People that claim HD is not what its cracked up to be usually are reacting to having seen such a plasma screen and extend that to the entire HD world. On larger 1366 x 768 plasmas at the 60 inch size you can really see each pixel and the black surrounding area. I would tend to favor the screens that look great at any viewing distance. Spend your money if you like what you see at 6 feet away.

DLP and Sony SXRD XBR2 almost totally eliminate this pixel to pixel separation, the whole Rear Projection tactic allows for that and they really do it quite well.

Sometimes things get bad...

THIS COLUMN written by some old guy in Baltimore sums it up pretty well, a huge 1366 x 768 screen was probably what he saw, with a rather dry and mildy irritating sense of humor.

THIS PAGE on Westinghousedigital.com actually lets you print out a full size picture of your tv, sort of taped toogether letter sheets to let you see how much space your TV really will need, and how big this is in relationship to your seating.

OK so what is what?
I think that from 37 to 55 inches, you are basically a TV watcher, typical of a lot of living spaces, and that from 55" on up you really are in a Home Theater kind of setup, where really the Screen takes over a typical room and becomes what the space is designed around. In my opinion this makes a sweet spot of LCD at up to about 4 feet of screen and Gives rear projection rigs like DLP and SXRD stuff an advantage at 60 inches on up.

I have read some posts elewhere that profess 1080p is too expensive, and i really need to point out that if you do the search, you can find great 1080p for a bit over 2k$.. My HD 1920 x 1080p Screen cost me $1298 and that was when it came out, you can buy it for less than that now. In 2007 i would guess that 37-42" screens with 1080p will likely hover around 1k, good deal i think. I paid 1800 for my RP Hitatchi in 1992 or so 45" NTSC screen, and thats a 480i, so in the big picture you are getting more for less if you seek out the great deals on 1080.

IMHO if you dont mind having to replace an expensive lamp maybe every 2 years, SXRD 1080p from Sony is superb.

PIXEL for PIXEL accurate HD1080p off Blu-ray or HD-DVD is worth it. Its is for the most part, the only way you can see what the director/producer intended. No scaling, no mucking with the image, every frame is a piece of art.

IF you can not see a difference between a 1 megapixel and 2 megapixel display at 8 feet away, then you really have less of a problem with resolution decisions. Probably you are more sensitive to black levels and contrast, and will prefer plasma or SXRD technology.

FINAL THOUGHT.
I have helped more than a few people over the past months, and comparison buying is in fact a challenging thing to do. Sometime in the spring i will create and release a Test HD-DVD and downloadable TEST File that lets you see comparative situations and excersizes the scaling and processing chipset in a display/player. Know why before you buy, and IMHO - pixel perfect is the best choice to assure no future regrets, since a TV is something you tend to keep for years.

2 Comments:

Anonymous Anonymous said...

that was awesome, you should be on TV.

9:29 AM  
Blogger Josiah said...

this helped me out SOOOOOOOO MUCH
i just typed in 1366x768 to actually look for wallpapers but this was the first link on google..
I've always wondered whether my laptop could output full 1080p, but I guess not! Still..it is slightly better than 720p I guess
thank you so much!!!!!!!!!!

9:15 AM  

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