Waveform 06 Display Terms Primer
Posted: Tue Jul 05, 2005 1:09 pm
Originally published 10/07/2004, HDTV Magazine, editor Dale Cripps
Updated 07/05/2005
By Richard Fisher
Before I dig into the different display types we need to define a few terms this week.
4:3 versus 16:9 screen shape:
If you purchase a 4:3 display, even if it is HD, you will take a hit in performance that will affect even the casual viewer. 16:9 is the preferred screen shape.
Burn in:
I am talking about portions of an image that remain on your screen regardless of the image that is presented. In the industry this is called image retention. This can be significantly reduced on CRT displays by simply turning the contrast down to about the half way point or lower. Many offer a movie, pro or home theater setting that will ball park the customer settings to about the right value. Varying the image content is very helpful.
Convergence:
the ability to put the red and blue picture perfectly on top of the green one to form one picture. Poor convergence causes red green, blue or secondary color outlines in the image reducing image resolution. Convergence is a function of CRT projection only.
Geometry:
the ability for a display to present perfect circles and squares any where in the viewing area.
HD CVD:
the critical viewing distance for HD content which for simplicity will be 3 screen heights.
Native scan rate:
In the past we had only NTSC video which uses 480I and comes in a variety of different connections and level of performance. Our displays have been 480I also and this is called the native scan rate. HDTV though is 720P, 1080I or 1080P and that means your HDTV has one of these native scan rates and possibly one more, 480P. There are few displays that do more than two. Connecting a 480I signal to a native 480I display is a straight forward process. Connecting that signal to an HDTV will not work until it has been converted to the native scan rate of the display. This process is called scaling and every HDTV has one that will convert most everything out there so you can view it on the display. We call this an internal scaler and they meet the requirements of casual viewing. Unfortunately many of the internal scalers are quite poor degrading the final image you see as a videophile. The way to get around that is to use an external scaler that does a far better job and set it to one of the native scan rates of your display. If you are a videophile you should budget $1000 for a scaler if you are not happy with the one in the display. If the display supports a native 480P scan rate then you can use a 480P DVD player and get excellent results as a casual viewer or videophile.
Overscan:
How much of the image is cut off beyond the borders of the screen which leads to loss of picture content. 1-3% is preferred but many CRT displays are 5-9%.
Pixel structure:
Only projection CRT does not have pixels. All other technologies do and many will not meet HD CVD. The ability to see the pixel structure is what has caused all the comments about plasma providing the sharpest image. This is an artifact due to visible pixel structure and nothing more.
Uniformity:
the ability for a display to have the same color of white everywhere on the screen. If you put up a gray field on the screen do you have the same color on the left and right, top and bottom sections as you do in the middle. This will be graded as high, medium and poor uniformity. Poor uniformity is considered potentially visible to even the casual viewer.
Front Projection:
These are two piece displays with the projector on one end of the room and the screen on the other. A dark room is required and will not work correctly in any other viewing environment.
VIEWING ENVIRONMENT
Bright room:
lots of windows during the day with plenty of sunlight
Medium room:
Some windows and darker areas during the day with some partial sunlight
Dark room:
you have full control over ambient light day or night. Normally very low ambient light to no light at all.
Light output rule of thumb:
The smaller the screen the brighter the image
Next week is CRT display technology.
LINKS
OAR, Original Aspect Ratio - Black Bars and Burn-in
viewtopic.php?t=3182
HD Library Video Dictionary
viewforum.php?f=69
If you have any feed back to this article please feel free to post your comments now by clicking on POST reply. All emails received concerning this article are open to being posted and published along with the article unless the sender requests otherwise.
Respect Our Copyright! DO NOT copy and paste this complete review or article to post or distribute. That is a violation of US copyright. Please feel free to quote small passages and please provide a link to the full review. Thank you!
Updated 07/05/2005
By Richard Fisher
Before I dig into the different display types we need to define a few terms this week.
4:3 versus 16:9 screen shape:
If you purchase a 4:3 display, even if it is HD, you will take a hit in performance that will affect even the casual viewer. 16:9 is the preferred screen shape.
Burn in:
I am talking about portions of an image that remain on your screen regardless of the image that is presented. In the industry this is called image retention. This can be significantly reduced on CRT displays by simply turning the contrast down to about the half way point or lower. Many offer a movie, pro or home theater setting that will ball park the customer settings to about the right value. Varying the image content is very helpful.
Convergence:
the ability to put the red and blue picture perfectly on top of the green one to form one picture. Poor convergence causes red green, blue or secondary color outlines in the image reducing image resolution. Convergence is a function of CRT projection only.
Geometry:
the ability for a display to present perfect circles and squares any where in the viewing area.
HD CVD:
the critical viewing distance for HD content which for simplicity will be 3 screen heights.
Native scan rate:
In the past we had only NTSC video which uses 480I and comes in a variety of different connections and level of performance. Our displays have been 480I also and this is called the native scan rate. HDTV though is 720P, 1080I or 1080P and that means your HDTV has one of these native scan rates and possibly one more, 480P. There are few displays that do more than two. Connecting a 480I signal to a native 480I display is a straight forward process. Connecting that signal to an HDTV will not work until it has been converted to the native scan rate of the display. This process is called scaling and every HDTV has one that will convert most everything out there so you can view it on the display. We call this an internal scaler and they meet the requirements of casual viewing. Unfortunately many of the internal scalers are quite poor degrading the final image you see as a videophile. The way to get around that is to use an external scaler that does a far better job and set it to one of the native scan rates of your display. If you are a videophile you should budget $1000 for a scaler if you are not happy with the one in the display. If the display supports a native 480P scan rate then you can use a 480P DVD player and get excellent results as a casual viewer or videophile.
Overscan:
How much of the image is cut off beyond the borders of the screen which leads to loss of picture content. 1-3% is preferred but many CRT displays are 5-9%.
Pixel structure:
Only projection CRT does not have pixels. All other technologies do and many will not meet HD CVD. The ability to see the pixel structure is what has caused all the comments about plasma providing the sharpest image. This is an artifact due to visible pixel structure and nothing more.
Uniformity:
the ability for a display to have the same color of white everywhere on the screen. If you put up a gray field on the screen do you have the same color on the left and right, top and bottom sections as you do in the middle. This will be graded as high, medium and poor uniformity. Poor uniformity is considered potentially visible to even the casual viewer.
Front Projection:
These are two piece displays with the projector on one end of the room and the screen on the other. A dark room is required and will not work correctly in any other viewing environment.
VIEWING ENVIRONMENT
Bright room:
lots of windows during the day with plenty of sunlight
Medium room:
Some windows and darker areas during the day with some partial sunlight
Dark room:
you have full control over ambient light day or night. Normally very low ambient light to no light at all.
Light output rule of thumb:
The smaller the screen the brighter the image
Next week is CRT display technology.
LINKS
OAR, Original Aspect Ratio - Black Bars and Burn-in
viewtopic.php?t=3182
HD Library Video Dictionary
viewforum.php?f=69
If you have any feed back to this article please feel free to post your comments now by clicking on POST reply. All emails received concerning this article are open to being posted and published along with the article unless the sender requests otherwise.
Respect Our Copyright! DO NOT copy and paste this complete review or article to post or distribute. That is a violation of US copyright. Please feel free to quote small passages and please provide a link to the full review. Thank you!