Software Waveform Monitor?

[Mike99]

Is there a software waveform monitor program that can analyze the video output of a PC & display its black levels & white levels?

I’ve searched & found some programs that display what is being captured. But I want to look at what is being sent out from the HDMI output to the HDTV. I have a home theater PC and both the video card & Windows Media Center have settings for 16-235 and 0-255 color space. I do not have any problems & everything looks good to me. But I’m curious how some of the settings interact with each other.

Video black levels appear to be correct and so do jpeg images. This also makes me wonder if jpegs images are output using 0-255 color while video is 16-235. IOW is the PC treating them differently.

Is there some cheap or free program that can show this information?

[jagabo]

AviSynth's Histogram() and VideoScope(). VirtualDub's Color Tools. Sony's Vegas has them.

MJPEG normally uses full 0-255 YUV internally, because that's what JPG images use. Most other video codes use the 16-235 range for Y, 16-240 range for YUV, and their decoders expand the contrast to RGB 0-255.

JPEG image decoders will keep the 0-255 range when converting to RGB for display. MJPEG decoders usually maintain the full 0-255 range in YUV too. But when the editor receives that YUV it thinks it's 16-235 and incorrectly expands the contrast.

[smrpix]

If your computer has the grunt (and unfortunately according to your specs it does not -- maybe they're outdated?) DaVinci Resolve Lite is a free, full power color corrector/grader that has all the tools you would want.

http://www.blackmagicdesign.com/products/davinciresolve/

Premiere Pro also has good scopes.

[smrpix]

Just re-read your post, you want to monitor as you play out? Nothing except a real waveform monitor I think. --Far from free.

[jagabo]

To monitor the actual output from the graphics card would require a hardware device between the card and the monitor. A waveform monitor that looked at the graphics memory wouldn't work because the graphics card may change the values before they are output. And when using video overlay the window on the the desktop where you see the video doesn't actually contain the video, it's just a "hole" through which the video is shown (the actual memory that contains the video is elsewhere).

What you really need to do is get a levels calibration image and video. You can use the video in this post for adjusting your graphics card's video proc amp settings:

https://forum.videohelp.com/threads/326496-file-in-Virtualdub-has-strange-colors-when-o...=1#post2022085

[Mike99]

I’ve adjusted the HDTV using various calibration discs & test patterns in both a Blu-ray player & the HTPC and everything appears proper. Both sources are sent to the HDTV’s single input through an HDMI switch.

The HTPC has settings for Pixel Format & Dynamic Range. I am using a YCbCr video Pixel Format which is 16-235 color. The Dynamic Range is set to 0-255, however the setting is grayed out because of another function that is enabled. I’m presuming it is still 0-255.

If I display a jpeg test pattern using the HTPC it appears that 0-255 colors are getting displayed. IOW black below 16 is visible.

Does the HTPC change the color space depending on the image source? My first thought was the YCbCr video Pixel Format only affects video and everything else is controlled by the 0-255 Dynamic Range setting.

But if the HDTV is adjusted to not display blacker-than-black, then how can I see black below 16 with a jpeg image? At least it seems that way.

It appears the video test patterns I have are not exactly the same. For example the black levels on the THX Optimizer found on some DVDs is slightly different than that on the Avia calibration DVD. Perhaps the HDTV black level is set just a bit lighter than it should be, which means jpeg black 0 could be perceived as something slightly darker than black 16.

Or could the jpeg color space be getting rescaled somewhere so that its black 0 is being changed to black 16, along with all the colors also being compressed?

This is why I’m curious as to what is really being sent to the HDTV.

[jagabo]

Does the HTPC change the color space depending on the image source?

If the graphics card is set to output YCbCr then any RGB source is converted to YUV before being sent to the HDTV. The 0-255 RGB range is compressed to YUV 16-235. YUV video sources are sent as they are. Then TV then converts YCbCr to RGB for display. Depending on how it's set up it will convert YUV 16-235 to RGB 0-255, or YUV 0-255 to RGB 0-255. Or anything else depending on how you have the TV's brightness, contrast, hue, saturation, and any other controls set.

But if the HDTV is adjusted to not display blacker-than-black, then how can I see black below 16 with a jpeg image?

Because the RGB 0-255 range was compressed to YUV 16-235 before being sent to the TV. Instead of 256 different shades of grey only 240 are sent.

[Mike99]

Does the HTPC change the color space depending on the image source?

If the graphics card is set to output YCbCr then any RGB source is converted to YUV before being sent to the HDTV. The 0-255 RGB range is compressed to YUV 16-235. YUV video sources are sent as they are. Then TV then converts YCbCr to RGB for display. Depending on how it's set up it will convert YUV 16-235 to RGB 0-255, or YUV 0-255 to RGB 0-255. Or anything else depending on how you have the TV's brightness, contrast, hue, saturation, and any other controls set.

But if the HDTV is adjusted to not display blacker-than-black, then how can I see black below 16 with a jpeg image?

Because the RGB 0-255 range was compressed to YUV 16-235 before being sent to the TV. Instead of 256 different shades of grey only 240 are sent.

If I understand correctly then, video black 16 looks the same as jpeg black 0. Which is why my photo image blacks look like my video blacks. I was concerned something was getting cutoff or crushed & I could not detect it.

I just tried several different settings on the HD 6450 video card. The “blackest” combination I could think of was setting the Pixel Format to PC Standard (Full RGB) and enabling the Dynamic Range & setting it to 0-255.

I used the .avi that you referenced to above, an HD OTA pluge pattern I recorded, and a DVD with the THX Optimizer. I played these using WMC7, WMP, & MPC-HC. I could not display blacker-than-black even with the HDTV’s brightness set all the way to maximum. It lightened up everything but the below black color bars never displayed.

I also used WMC7's built in setup video which displays the person in a black shirt with the moving B-T-B letter X. With the TV brightness all the way up you could just barely see the moving X. But for all practical purposes it was not visible.

Playing the same DVD with the THX Optimizer in my Blu-ray player it was easy to adjust the TV’s brightness in order to see the B-T-B parts of the THX image.

So the TV can display B-T-B, but for some reason the HTPC cannot output B-T-B. Before I installed the video card I was using the Intel integrated graphics & IIRC was able to see the WMC7 setup video’s moving black X. There must be a video card setting that has to be enabled in order to output B-T-B. It’s probably a moot point because there should not be any B-T-B content in the video image anyway. But it would be nice to know what it takes to do that. If it were not for the Blu-ray player it would be difficult to adjust the TV for a proper black level.

[jagabo]

If I understand correctly then, video black 16 looks the same as jpeg black 0.

Yes.

So the TV can display B-T-B, but for some reason the HTPC cannot output B-T-B.

Are you sure the computer is putting out YCbCr, not RGB? HDMI can carry either. If it's putting out RGB BTB will be crushed before sending it to the TV. I have my HTPC set to output RGB to get the sharpest picture (Cb and Cr are usually carried at lower bandwidth, blurring colors).

There must be a video card setting that has to be enabled in order to output B-T-B.

Could be. I'm not too familiar with ATI's video options. It's possible the card/drivers automatically remove BTB content (ie, Y<16 is converted to Y=16).

[Mike99]

There appears to be 2 functions that could affect color space. One is called “Pixel Format“ & there are 4 choices. Previously I tried all of them & the first 3 behave the same. Number 4 makes the image darker.
1. YcbCr 4:4:4 Pixel Format
2. YCbCr 4:2:2 Pixel Format
3. RGB 4:4:4 Pixel Format Studio (Limited RGB)
4. RGB 4:4:4 Pixel Format PC Standard (Full RGB)

I have been using #1, but for my recent experiments I also used #4.

The other function is Dynamic Range & it’s either 0-255 or 16-235.

The only thing that seems to make a difference is changing Pixel Format to #4 which make the picture darker.

[jagabo]

Numbers 1 and 4 should look the same (except that you won't ever see blacker-than-black with #4). Number 2 should have slightly blurry colors (when displaying 4:4:4 sources like the Desktop). With 1 and 2 you should be able to adjust the TV's controls to see blacker-than-black. Number 3 should have lighter blacks, and darker brights, you should be able to see blacker-than-black and brighter-than-bright by adjusting the the TV's controls.


Chroma subsampling:
https://forum.videohelp.com/threads/294144-Viewing-tests-and-sample-files?p=1792760&vie...=1#post1792760

[Mike99]

I thought about something late last night. I’ve been using 0-255 Dynamic Range thinking that B-T-B is in the 0-15 range. That 16-235 could not display anything below 16 which is why it could not display B-T-B. But maybe I was looking at things wrong, and apparently I was.

I changed the Dynamic Range to 16-235 and now I get B-T-B with all of the Pixel Format settings.

Pixel Format #4 with 16-235 DR appears to display the same blacks as Pixel Formats 1, 2 & 3 when using 0-255 DR.

With the 16-235 DR, Pixel Formats 1, 2, & 3 need the TV’s brightness decreased in order to match Pixel Format #4 using the TV’s current brightness setting.

You mentioned that #1 and #4 Pixel Format should look the same, except that #4 will not show B-T-B. However from all my experimenting #1, 2, & 3 have always looked the same regarding B-T-B. If there are slight differences in how dark the blacks are it is not something that I have been able to notice. But #4 always had a darker look to it, and with the 16-235 DR the B-T-B is visible if I increase the TV’s brightness.

I’m still not sure how a smaller range allows for B-T-B but it obviously does.

I did look at the chroma sub sampling link that you provided. If there are no 4:4:4 video sources then why would you choose Pixel Format #1 or #4?

Thank you for all the information.

[jagabo]

I did look at the chroma sub sampling link that you provided. If there are no 4:4:4 video sources then why would you choose Pixel Format #1 or #4?

1 and 4 would look identical. Well, there would be slight differences. RGB sources would lose a little color accuracy when output as YUV 4:4:4 since YUV uses a narrower range of values. For example, an RGB image can have 256 levels of grey (0-255). But a YUV image can only have 240 (16-235).

Here's what I do when calibrating levels by eye:

1) Set the graphics card's proc amp settings all to their neutral position (Desktop and Video). Turn off all video processing settings like edge enhancement, auto contrast, noise reduction, etc.

2) Set the graphics card to output RGB. These first two steps should assure that the Desktop RGB graphics are sent to the monitor unmolested.

3) Set the monitor's proc amp settings all to neutral. Turn off all video processing settings, especially automatic brightness and contrast features. This should assure that the incoming RGB image is displayed without being "enhanced".

4) Use a 256 grey level BMP image to adjust the monitor's brightness and contrast settings so that the blackest patches are as black as the TV can display, the brightest whites as bright as the TV can display. Nearly all 256 grey levels should now be distinct. Be sure the program that's displaying the image isn't "enhancing" it*.

5) Use a 256 grey level YUV video (with blacker than black and brighter than bright) to adjust the graphics card's video proc amp so that Y=16 is the blackest black, Y=235 is brightest bright.

Here's are a few RGB levels calibration images you may find useful.

Selected darks and brights:


256 shades of grey:


* Windows' Photo Viewer isn't good for displaying images. It changes the levels slightly. There's a tool called CSamp which will let you read RGB values off the Desktop. That will at least let you verify that the program displaying the image isn't screwing with it.

[Mike99]

I am using the HDMI input on my HDTV & do not have any automatic settings enabled. FWIW there is no option to select either a video source or a PC source.

The PC’s video card does have a few processing settings enabled by default. So far I have left them that way because the picture looks quite good. But I will disable them.

You mention “ RGB sources would lose a little color accuracy when output as YUV 4:4:4 since YUV uses a narrower range of values.” Does that mean that #4 with Dynamic Range set to 16-235 should look the same as #1 with Dynamic Range set to 0-255?

Regarding step 5. How do I get a 256 step gray level YUV video if YUV uses only 16-235?

If video black 16 looks the same as jpeg black 0 does that mean that video black 0 is actually darker than jpeg 0?

[Mike99]

If your computer has the grunt (and unfortunately according to your specs it does not -- maybe they're outdated?) DaVinci Resolve Lite is a free, full power color corrector/grader that has all the tools you would want.

http://www.blackmagicdesign.com/products/davinciresolve/

Premiere Pro also has good scopes.

I just updated the specs of the computer I'm using for the HTPC. I forgot that information was listed here. Sorry about that.

[jagabo]

You mention “ RGB sources would lose a little color accuracy when output as YUV 4:4:4 since YUV uses a narrower range of values.” Does that mean that #4 with Dynamic Range set to 16-235 should look the same as #1 with Dynamic Range set to 0-255?

I don't really know what your graphics card and TV are doing.

Regarding step 5. How do I get a 256 step gray level YUV video if YUV uses only 16-235?

There's nothing to stop you from putting values from 0-15 and 236-255 in a YUV video. But by definition, Y=16 is full black; values less than that should be rendered the same shade of black. Y=235 is full brightness; values over that should be rendered the same brightness. The idea was simply to have a little footroom and headroom for overshoots.

[hello_hello]

There appears to be 2 functions that could affect color space. One is called “Pixel Format“ & there are 4 choices. Previously I tried all of them & the first 3 behave the same. Number 4 makes the image darker.
1. YcbCr 4:4:4 Pixel Format
2. YCbCr 4:2:2 Pixel Format
3. RGB 4:4:4 Pixel Format Studio (Limited RGB)
4. RGB 4:4:4 Pixel Format PC Standard (Full RGB)

I have been using #1, but for my recent experiments I also used #4.

The other function is Dynamic Range & it’s either 0-255 or 16-235.

The only thing that seems to make a difference is changing Pixel Format to #4 which make the picture darker.

If it works anything like my TV and video card (Nvidia)......

If the PC output is YcbCr or YCbCr the TV expects TV levels (16-235) and doesn't give me the option to change that. The video card dynamic range setting should also be TV levels (16-235). Video will display correctly. Windows itself will look a little "off" as it always uses PC Levels (0-255). The video card output setting only effects video.

If the PC output is RGB then by default my TV still expects TV levels (16-235) using HDMI and the input level can be set for each HDMI input individually. I think all TVs expect TV levels by default. Windows itself may look a little "off" as it always uses PC levels (0-255). With the output as RGB the TV gives me the option to choose the input level. If I switch the TV's input setting to PC levels (0-255) and the video card dynamic range to PC levels (0-255), then both Windows and video display correctly.

The input setting for many TVs can be counter intuitive. Mine's labelled as "HDMI Black Level". You'd possibly assume a black level labelled "normal" would be TV levels, given it's a TV, but that's not the case for my TV. "Low" = TV levels, "Normal" = PC levels. The TV defaults to "Low".
So for me.... TV HDMI Black Level = Normal. RGB output, Dynamic Range = PC levels (0-255) and everything displays correctly.

Of course it's possible for a media player to expand the levels too. For instance MPC-HC using the EVR renderer expands video to PC levels by default, but setting the video card to output PC levels (0-255) too won't do any harm, it probably just won't change the way the video is displayed if the media player is already expanding the levels.

PS. You can match the PC output and TV input levels by playing video which uses black borders and changing the TV input/PC output levels. Preferably while ensuring the video player is not expanding the levels. The black borders should be black, not dark grey. Depending on how the output/input levels are set, video will display one of three ways (assuming the TV is not too far off calibrated).
1. The black borders will look black and the picture will look dark. 2. The black borders will still look black but the picture will look brighter. 3. The black borders will look dark grey and the picture brighter again. The second one is where the levels "match".

PPS. The one exception is VGA inputs on TVs. Like PC monitors they seem to always expect PC levels with no option to change that.

[NJRoadfan]

If you are looking for a cheap external device, see if you can find a DPS "Personal V-Scope" card, it is a passive ISA card that is controlled by RS-232 serial. It features a waveform and vectorscope monitor and just requires a composite monitor to view. The card was popular back in the day with Video Toaster users to monitor levels. I personally have one here installed in the empty bay of a DPS-235 TBC and use a Video Toaster as a test signal generator. The card included Amiga software that generates the various test patterns as Video Toaster frame stores. The RS-232 control software for the card itself is available for DOS, Windows, and Amiga.

[Mike99]

hello_hello -

My HDTV has a single HDMI input and there is no setting for choosing TV or PC levels.
I too have sometimes used the TV’s black borders as a reference for black.

NJRoadfan -

Problem is I’d have to put the card in the HTPC I am using. I don’t think it would be able to monitor the PC that it’s installed in. Even if it could there are no free slots available.