IRE Help! Still Confused.....

Originally Posted by JohnnyBates

Currently my analog captue setup is as follows

VCR > MiniDV camcorder passthru via firewire > PC

I use WinDV as my capture Software.

I use CCE SP2 to encode the footage for DVD.

I've been through all of the IRE posts. I'm still confused.

My VCR outputs IRE 7.5. The MinIDV Camcorder converts the 7.5 IRE to 0 which mean the black on the capture will be darker than whats on my VHS source tape.

Am I correct so far?

Then, I encode to Mpeg 2 for burn onto DVDR.

My question is this. Do I need to/should I adjust the black level in an .avi editor prior to my Mpeg encode to ensure the IRE matches the VHS levels of the source? Or - will the dvd player adjust the IRE to 7.5 when it plays the burned DVD back on my TV?

If I do need to adjust black levels - please suggest software methods to do this in a way that I can ensure I hit the correct IRE level.

Thanks!

E

I can partially answer your question.

NTSC VCR outputs 7.5 IRE black and 100 IRE white in analog.

A NTSC DV camcorder in "Analog Pass-Thru" mode will not compensate for 7.5 IRE inputs. It will capture 0 IRE to digital level 16 (DV and DVD black reference) leaving 7.5 IRE to map to digital level 32 (a dark gray).

Correction can be done in the DV format with a levels filter, or in the encoder settings if it has a mode that compensates for a 7.5 IRE input.

I haven't used the CCE encoder for awhile so I can't speak to its settings.

If you see your DVD black levels "washing out" or appearing gray relative to a commercial DVD or a normal TV broadcast, then you need to adjust your black level after capture.

I just did a google search and found a reference to a luminance switch in CCE basic that allows either

"16-235" assumes normal DV/DVD levels coming in.
"0-235" attempts to correct for non-standard black on level 32.

Either this switch corrects it in the right
direction or makes it worse. I don't have the encoder to test it. I would think the correct name for this switch would be "32-235" or "32-255".

This may be the kluge solution if you are just editing black level 32 clips. If your edit includes black level 16 clips from another source (such as the camera section of the camcorder), this switch may encode those clips too dark.

That is why it is best to adjust everything to 16-235 at capture before you edit.

Originally Posted by marksk918

so, if i use the levels effect in adobe premiere 6.5, for the rgb channels, i'll set the black input level to 32 and the black output level to 16, the white input level to 255 and the white output level to 235. is that right or am i still confused?

Sounds right, I'll try it on my Premiere 6.5 (different computer) when I get a chance. I wish 6.5 had the scopes.

OK here is my first pass with Premiere 6.5. I checked the results with Vegas monitors using DV-AVI files, not MPeg2.

Capture: Here is a typical DV camcorder "pass-thru" capture of a 7.5-100 IRE cable channel. Black maps to 32 and white is near 235 digital levels. This is the typical "wash out" senario. If this is encoded to DVD as is, the DVD player will play out with 15 IRE blacks.




First filter tried is the Premiere 6.5 Levels filter (Video-Adjust-Levels) set to 32 and 235.




The result appears to set black to 16 and leaves white at 235 as desired.
Remember that this needs to be eyeballed on a TV monitor connected to the camcorder or off a test DVD burn.

Originally Posted by hrlslcbr

Originally Posted by edDV

I just did a google search and found a reference to a luminance switch in CCE basic that allows either

"16-235" assumes normal DV/DVD levels coming in.
"0-235" attempts to correct for non-standard black on level 32.

Either this switch corrects it in the right
direction or makes it worse. I don't have the encoder to test it. I would think the correct name for this switch would be "32-235" or "32-255".

Are you sure about this? I've tried encoding the same material twice, with 0-255 and 16-235 and they don't look different. That is if you use YUY2 sources; if you yse RGB, the 16-235 option seems to compress the range, while the 0-255 one leaves the colours unchanged.
I'll e-mail cinemacraft to ask them about these options.

No I'm not sure what the settings do in CCE. I don't have it here to test.

Originally Posted by hrlslcbr

Ok edDV, I'm afraid that what you read is not correct.
Cinema craft's tech support said:

'Cinema Craft Encoder uses a YUY2 pixel format internally. If
the source format is RGB, the color space conversion into YCbCr
will be performed using this lumimance range.'

So if you select 0-255 CCE won't change the Y range, but if you select 16-235, it will 'compress' the luma.
This setting doesn't affect YUY2 sources.

Well I wasn't claiming any knowledge of CCE settings.

"but if you select 16-235, it will 'compress' the luma." What do they mean by that? The main issue is that your DVD gets encoded to 16-235 Y levels if you want a standard DVD.

Originally Posted by marksk918

Originally Posted by hrlslcbr

This setting doesn't affect YUY2 sources.

i'm sorry, newbie here, is dv a YUY2 source?

YUY2 is uncompressed YUV 4:2:2. DV is a compressed form of YUV with 4:1:1 sampling.

Inside applications like Premiere, DV may get decompressed to YUV or RGB when image processing is required. Premiere up through v6.5 used mostly RGB processing. Premiere Pro v7 and above are native YUV but still convert to RGB for some processes. When the processed portions of the timeline are rendered, such as during preview or "export to movie", uncompressed YUV and RGB portions of the timeline get re-encoded to DV format.

That is my understanding.

So marksk918, are you getting good results from the Premiere 6.5 levels filter?

I'm just curious to see if it worked for you.

Good, here's another example of a DV camcorder capture.
Premiere 6.5 Levels filter only. Left is before, right is 32-235 setting.





And here it is on the Vegas waveform monitor.

Originally Posted by JohnnyBates

Oddly enough the black levels look fine on my VHS>MiniDV Passthru>PC captures whcih are then burned to DVD and played on my TV (professionally calibrated). Blacks are solid black..no washed out/grey blacks.

Perhaps the Analog-Input on my camcorder is compensating?

E

Could be. What is your camcorder model? Are you sure you don't see a black shift going from DV capture DVD to a commercial DVD?

One possibility is your encoder may be compensating.

Of course this applies only to NTSC DV camcorders. JVC claims to be the only company doing it correctly at the prosumer level.
http://pro.jvc.com/pro/attributes/prodv/clips/blacksetup/JVC_DEMO.swf

Here is a full grayscale range typical capture.

I've been watching this thread with some interest. I don't have Vegas and I don't have any money. Do you know of any freeware way to check the levels of an existing video? I know that the Levels filter of VirtualDub allows you to sample either a frame or the whole video, but I have no idea what the graph that gets displayed represents since there are no reference points identified.

Here is a Vegas levels 7.5% correction to black level.



and the result. More could be done to enhance this clip. I'm just looking at black level here and it needs to be seen on a TV for full effect.

hrlslcbr wrote:

@gadgetguy: You can view the levels with avisynth.

Thanks. I used the histogram() command and viewed my raw footage. I was a little confused at what I was looking at, but with some experimentation it appeared that the footage was captured at levels 32-255 (approx). Here is a screenshot.


I then applied the Levels filter like this:

Levels(32, 1, 255, 16, 235, coring=false)

And the resulting histogram looks like this:



If I've followed this thread as well as I think I have, this is the proper outcome I'm seeking, correct?

FWIW I put those two frames on the Vegas WFM (black 16 - white 235)

I'm not sure what this input waveform is.

b4 - black at 16, white at 255


after - black at zero, white at 235 (i.e. lunimance waveform moved down 7.5 IRE or 16 digital levels).