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HD Test Patterns!


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9 replies to this topic

#1 OFFLINE   jsanders

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Posted 28 January 2004 - 01:49 PM

Have you been wanting to calibrate your set with HD test patterns, but you don't want to buy a Digital VHS, and plunk down $100 for Video Essentials on top of that??

Just record this on HDNet:

Tuesday, Feb. 3, 8:00 AM ET / 5:00 AM PT

HDNet Test Patterns
Wonder how your home theatre is doing? Wish you had test patterns to help set it up? Well, HDNet is here to help. This short program will help you get the most out of your home theatre setup by providing you with the same professional test patterns HDNet uses to set their gear.

I did mine by upconverting Video Essentials by plugging it into the 921, but this will be far better.

...Ads Help To Support This SIte...

#2 OFFLINE   BarryO

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Posted 28 January 2004 - 04:12 PM

Thanks for this post!!!

This is will be just as good as having a multi-$1000 HD test pattern generator to calibrate your settings.

The 921 component out has darker blacks than the 6000's; I still don't think I see any blue lines but I'm not happy with the black levels and the resulting PQ. It should be possible to adjust them with these signals.

#3 OFFLINE   JohnH

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Posted 28 January 2004 - 04:34 PM

You get split field color bars with gray scale, convergence pattern and resolution pattern.

Sometimes HDNET runs it at other times, but the Tuesday shows in the EPG regularly. It runs about 10 minutes. Thanks to Zenith. :)

#4 OFFLINE   metallicafreak

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Posted 28 January 2004 - 07:46 PM

HOw do you use these patterns to set the color/tint/brightness/contrast? I recorded them and am not sure how to use it.
FREAK!

#5 OFFLINE   pculley

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Posted 29 January 2004 - 08:40 AM

Unfortunately the patterns provided on HDNET are not ideal for the purpose, however, here is an excerpt from the Avia DVD test pattern descriptions that may help.

Setting white and black level should be done with a grey steps pattern or some other pattern with a range of black/grey/white.

Setting black level (brightness or picture) involves finding the blackest portion of a full range test pattern, and then adjusting it so that the screen is just barely beginning to glow; for SD TVs, the raster lines just barely show in an almost black screen. For HD sets, the raster lines may not show at all, and this should be set to be right at the point where lowering the level no longer darkens the screen, but raising it begins to brighten the screen.

Setting white level (Contrast) is usually more difficult, in that high settings cause various distortions. The maximum level for best picture is usually much darker than you would expect (you might opnly be able to watch in a dark room). Thie following is some stuff to watch for when setting white level.
1. Prevent doming (change in color of white due to overheating)
2. Avoid blooming (widening or blurring of log steps)
3. Remain in linear range (each successive step should be 1/2 as bright)
4. Avoid white clipping (disappearance of white bars)
5. If possible, avoid geometry distortion (bending of vertical lines)

AVIA Obscura #2 - Blue Bars, Red Bars, Green Bars

NTSC video signals must be separated, decoded, and matrixed to form the final red, green, and blue signals which drive the display. Professional grade displays accurately decode the color signals and render colors correctly. However, consumer grade televisions often break the rules and have non-standard color decoding. This is most often seen as exaggerated reds (red push) and wreaks havoc when one attempts to adjust colors on a consumer display using just color bars.

Color bars are encoded such that the amount of red, green, or blue is 75% in each bar which contains the color. For instance the amount of blue is 75% in the gray, blue, cyan, and magenta portions of color bars. Similarly, the amount of red is 75% in the gray, red, yellow, and magenta portions. Because the amounts of each primary are identical in the various patches, one can compare the intensity of each color to learn how a decoder is functioning.

75% Gray has zero color difference from gray so adjusting color saturation up and down doesn't alter its appearance. Hence, gray serves as the reference point against which the intensity of color saturation may be compared. Turning saturation up and down alters the intensity of the colored portions of color bars. View the blue portions of color bars in blue-only as you increase saturation. This can be done with a blue filter, or with the blue gun only setting of your tv (this may only be available in a service mode). You'll notice that blue increases in intensity with increasing saturation. When saturation is correctly set, the intensity exactly matches that of gray. On a professional display with NTSC accurate color decoding, this same saturation setting also makes the red and green portions of the pattern match gray (whn viewed with appropriate filters or single gun mode). Hue is adjusted by comparing portions of the pattern that contain two primaries such as cyan vs magenta.

AVIA Obscura #3 - Sharpness Pattern

NTSC video carries most of its resolution in the luminance portion of the signal. Onto this is overlaid lower resolution color information to yield the final picture. By doing this, the designers of the NTSC system were able to provide an image which gave much of the perceived effect of having high resolution in both color and luminance but in a smaller amount of bandwidth.

Television displays provide a sharpness or peaking control whose behavior is much akin to the treble control of an audio receiver. The control should be used to compensate for the attenuation of high frequency video information that blurs images horizontally. Unfortunately, this control is often misused or not designed in a way that accomplishes this goal. Users often keep sharpness set too high and suffer a picture that appears sharper to the naïve eye, but is actually filled with extraneous image artifacts. Sharpness is perhaps the most difficult control to teach people to set properly.

There are often recommendations to simply turn sharpness all the way down, but that can be excessive. It's best to actually use a test pattern which points out how the sharpness control is altering the image. Then you can rationally determine optimum setting on your display. AVIA provides a dedicated Sharpness pattern which combines several tests of parameters important in determining optimal sharpness setting.

1. A horizontal frequency sweep occupies the top of AVIA's sharpness pattern. This is a constant amplitude sweep that goes from low video frequency to high video frequency. If the video bandwidth of your display is lower in a portion of the video bandwidth, then that section of the sweep appears darker. Ideally, the brightness of the sweep is constant throughout its range. As you adjust sharpness up and down, look to see if any portion of the sweep goes up and down in brightness. That is the set of video frequencies the sharpness control of your display affects. If your display's sharpness control is well designed, all you need do is adjust to make the sweep as evenly bright as possible.

2. Some people find it difficult to compare different sections of a sweep because the gradation of brightness is continuous from one section to another. The frequency bursts at the bottom of the chart provide discrete patches of video frequencies that can be compared. You'll probably find that the rightmost patch is slightly darker than the rest of the patches even on the best of displays. Just try to equalize the other patches.

3. There are black vertical lines, diagonal lines, and a circle in the center of the AVIA sharpness pattern. These are needed because many sharpness controls not only alter frequency response but add ringing artifacts. Ringing is overshoot and undershoot of the video signal at abrupt luminance transitions. You see this as false outlines next to the actual black lines. If setting sharpness at the point which equalizes video bandwidth also yields visible ringing, you should decrease sharpness to the point at which the false outlining is just barely visible. Otherwise, you will be adding artifacts rather sharpening actual image detail.
4. There are also vertical lines set against black and white backgrounds. These are also used to look for ringing, but because the luminance transitions are larger than going from a gray background to black, these serve as especially severe tests for ringing. These are primarily for testing display circuit design quality rather than for actually setting the sharpness control, because these are usually too severe a test for consumer grade displays. Setting sharpness low enough to avoid all outlining of black/white transitions will often yield an excessively blurred image on consumer grade displays.

5. A vertical frequency sweep occupies the left side of the pattern. This is used in conjunction with the horizontal lines of the pattern to set vertical aperture (vertical sharpness) of video processors which have this control. As with the usual sharpness control, adjust to equalize video bandwidth and avoid false outlining.

Once you have correctly set sharpness, it is very tempting to return to your previous excessively high setting. Don't. view the picture several days at the new, less artifact inducing setting. You will find that the old overly high setting yields an unnatural picture.

Properly adjusting the sharpness control is only part of getting maximal image detail from your display. Keeping white level below the point of blooming and controlling room lighting should also be done. Once all these are done, you might wish to measure your display's resolution using resolution patterns which I'll cover in another AVIA Obscura.

#6 OFFLINE   Mark Lamutt

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Posted 29 January 2004 - 11:58 AM

Now that Feb 3rd has passed, moving this thread to the Technical Talk forum. HDNet broadcasts these test patterns every other week or so (at least that's how often I've seen them).

An interesting story here about the test patterns. About a year and a half ago, the Denver HDTV Users Group (which I am a part of) went on a tour of the HDNet broadcast facilities here in Denver. On the tour, the techs asked us how we calibrated our HD sets. At the time, really the only options were to upconvert VE or AVIA with an HTPC to 1080i/720p, or to play back VE/AVIA from DVD player through a VCR to convert to RF out into the antenna port of an HD satellite receiver to be upconverted to 1080i/720p. Neither one were great options, and we told him so. He asked us if there would be any interest if HDNet were to take 10 minutes a week or every other week and broadcast some test patterns for use. And the rest is history...of course we jumped at that and starting the week after our tour, the test patterns were put on the air.
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#7 OFFLINE   pculley

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Posted 29 January 2004 - 01:05 PM

He asked us if there would be any interest if HDNet were to take 10 minutes a week or every other week and broadcast some test patterns for use. And the rest is history...of course we jumped at that and starting the week after our tour, the test patterns were put on the air.


If you have a name, email address, or can contact him, I would suggest adding a color bar chart that is more similar to the standard SMPTE bars. The traditional SMPTE color bar includes not only bars but small patches of colors which are in reverse blue order just below the color bars. This helps immensely when adjusting the color levels since the colors to match (when viewing filtered) are adjacent to each other. With the bars they show now, you have to match colors on opposite sides of the screen...

#8 OFFLINE   jsanders

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Posted 04 February 2004 - 08:13 PM

Tuesday has come and gone, and I'm sure there are some out there that managed to record the test patterns... They are obviously not as complete as hoped. I am curious though about how good your TV sets are!

Can anyone read the last line in the convergence test? It is supposed to say something like, "10. your monitor is better than mine"

My set, a Panasonic 34" direct view can show the next to the last line, "9. If you can read this", however, I can't really make out the letters of the aforementioned last line. I can make out the shapes of the words, but I honestly wouldn't say it does a good job with it.

How good is your set? If it can do it, what set do you have? Inquiring minds want to know!

#9 OFFLINE   JohnH

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Posted 04 February 2004 - 08:30 PM

I can read it on my 15.5" viewable computer monitor with the 6000. Don't have a TV per say.

#10 OFFLINE   jsanders

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Posted 04 February 2004 - 08:48 PM

I can read it on my 15.5" viewable computer monitor with the 6000. Don't have a TV per say.


That is expected I would think. It is really irritating that the TV manufacturers haven't used the technology from monitors so far! The monitor has been able to handle high bandwidth signals for a long time, and the convergence is steller. Sony, for instance, makes monitors and TVs. Why can't they just make a 34" monitor and call it a TV, it would be great!

So far, It think the best HDTV display at the moment is probably the Apple 23" computer monitor, as it actually has 1920x1080 pixels on it. Okay, it has a couple hundred *more* lines than 1080, but who is counting (nobody with a plasma display that doesn't have a 16x9 pixel ratio)! The only problem is that it is 23"! Maybe TFT displays will get big enough to use as a TV someday soon.




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