GH2 GH2 HDMI Capture strange behavoiur with luma channel

T

tbruegg

Member
I captured on the HDMI port with a decklink intensity. it seems that the luma channel is cropped at -5 in the RGB MJPEG Codec while the colour channels are o.k. look at the waveform:
waveform.gif


Capture Uncompressed comes with same results must be in the signal, anyone with AJA Card who could test this? any ideas?

Thomas
 
it means that we wont be able to:

- record to a external recorder through the hdmi port(unless you dont mind crushing dark areas and possibly white)
- have a valid external-monitor view with hdmi monitor, also false colour on a dp6 will show you wrong values.

If anyone with a capture card other than the bm-intensity or with an external recorder could check it would be great then we know for sure.

Thomas
 
i have to add that when a clip is played back from the camera and captured via hdmi port the signal is clean!! only in live view mode where the signal IS IMPORTANT its not clean, or let me correct it COULD be not clean. please someone check again.
 
I'm not sure I follow, how does that waveform show black level clipping? Why does the signal seems to extend almost as low as -20? That doesnt seem legal but it you could probably recover it if your software is seeing it...

What is the significance of the line at ~-7?
 
the capture codec is rgb black would be at -20 white at 120 anyway the waveform shows the luma and the chroma channels, while the chroma channels are as they should be, the luma channel is clipped at around -5 there is nothing to recover its clipped allready as it hits the card, its not the codec i've tested several codecs. and the hdmi signal is clean when the camera is in playback mode. Im still waiting for someone to confirm or to make this a problem of my gh2.
 
UPDATE

while playing around with the DP6 Monitor in false colour mode, i found that when the camera records the clipping goes away and the signal seems to be fine, have to check with the card and the waveform monitor but thats good!
 
Problem solved.

The blackmagic codecs are the problem dont know why, have to send BM a mail. But be aware the camera has a funky behaviour, it sends RGB while not recording, when recording the signal changes to YUV levels.
 
Edit: I found this forum thread regarding GH2 and HDMI, so might be a good idea to bring your findings there? I posted a link to this thread over there, hope it's ok.

tbruegg said:
Problem solved.
The blackmagic codecs are the problem dont know why, have to send BM a mail. But be aware the camera has a funky behaviour, it sends RGB while not recording, when recording the signal changes to YUV levels.
Click to expand...

Interesting, thanks for sharing. I've got a BM extreme hd capture card, and hopefully I will find the time to test hdmi capturing with GH2 soon.

I haven't any experience with RGB vs. YUV levels. Is it recommended to capture in YUV in general? If I do HDMI capture, it's not important for me to record on the GH2 anyway..

Keep us posted regarding feedback from BM on the codec issue :)
For now, which codec do you use instead?
 
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Sorry, working days are too bussy, and haven't had the gh2 and the capture pc available at the same time yet. But I'll post my findings here as soon as I have the time and equipment available.
 
hdmi

hdmi

Again, another mountain out of a mole hill. Monitors are NEVER a 100% accurate representation of what you're shooting. Never. Not with the red. Not with film. It's just never perfect.

That's what color correction is for kids.
 
Finally had the time for a quick initial test, and at least I got it working pretty quickly (using black magic decklink extreme hd). I also noticed the visual change, especially in black levels, when the GH2 was in "standby" and record mode. At first I thought the standby mode gave the best quality because of more saturated blacks, but as I see from other postings here, if this is the result of clipping and other bad things, I guess we should stick to capture while recording on camera (giving the YUV-signal as I understand it).
I didn't have the time for checking other than 1080 50i setting (it's a PAL), so as far as I can see I'm not affected by any frame skipping issue like the NTSC 59.97i/60i issue seem to create. I will try more settings (will try progressive, but seemes like it doesn't work for others?) soon, and also trying some footage against vectorscope info (but I'm not so experienced in reading those).
 
...you mean with standby mode.... liveview? btw. many thanks for testing, interesting too that's a GH2 Pal version.
 
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This defeats the purpose of having a HDMI capture since it is reading the AVCHD stream.

tbruegg said:
i have to add that when a clip is played back from the camera and captured via hdmi port the signal is clean!! only in live view mode where the signal IS IMPORTANT its not clean, or let me correct it COULD be not clean. please someone check again.
Click to expand...
 
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