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BMD HDlink Pro - major problem

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Author Steve
Scene
#1 | Posted: 12 May 2012 10:46 
At present, there is a major problem with the HDlink Pro LUT box.

This problem has been reported to BMD some time back, but as yet no solution has been presented.

The problem is that when a LUT is loaded into the HDlink Pro it is badly distorted, causing the output to be inaccurate to the actual intentions of the LUT.

This makes the HDlink Pro box unusable for any LUT application.

If BMD find a solution to this problem I will post it here.

Author Dermot
Mono
#2 | Posted: 14 May 2012 17:00 
This is a bit worring to me... can you shed some light (pun intended) on what the issues are?

I have 5 of the BMD's , and do use the LUT at times, and at times run the same LUT in my timeline, attached to clips and/or outputs.

Is this easly seen by eye, or more subtle and picked up by a probe?

Author Steve
Scene
#3 | Posted: 14 May 2012 17:38 
Hi Dermot,

The problem can be easily seen by eye, depending on the LUT in use.

The main problem is when looking at the HDlink output there is bad clipping in the blacks, and colour distortion - especially in the grey scale.

The black clipping happens when the LUT has a small 'toe' component (the grey scales ramp is not linear), but has no clipping actually within the LUT.

Use the 'BrightnessCal' image from the Calibration Images downloads to see the problem. It will be very obvious.

I don't use Resolve, so I guess it is possible that has the same problem? I've never tested...

Author John_Michaelt
Mono
#4 | Posted: 15 May 2012 15:32 
I've seen this as well with all of our LinkPros. I've netted out in the most practical rationalization I can for the time being. The linkpro with a good calibration LUT is generally better than no LUT in line at all, but for very critical applications we use a Davio or run the LUT internally in Resolve or Lustre. However, Lustre has its own bug when running the LUT internally if not using log based footage and selecting as much in the prefs.

I recently tried profiling an OLED and running the LUT in a linkpro and very quickly realized the OLED was much better with no LUT at all, just some manual tweaking. Granted, this was for on set reference to a calibrated theater.

Author Steve
Scene
#5 | Posted: 18 May 2012 07:09 
BMD have got back to us, and have said they are indeed looking into the LUT problem, stating it is definitely something BMD want to address.

Finger's crossed a fix is coming!

Author Dermot
Mono
#6 | Posted: 29 May 2012 22:54 
Steve
ThanX Steve

my pinkies are crossed too

Author Jay Friesen
Mono
#7 | Posted: 3 Jun 2012 05:33 
Thanks for the update Steve. I have a project I'm grading in June. I'll look into a different solution if a firmware update hasn't coming out yet as a fix.

Author Dermot
Mono
#8 | Posted: 3 Jun 2012 23:02 | Edited by: Dermot 
I'm fence sitting for a few more weeks... conundrum is spending coin on;

300 series PanaPlasma + HDlink (to take dualink to HDMI) + Lightspace with the LUT inside the PanaPlasma (about 9K more than i budgeted)
-or-
current mon's + ColorBox + HDlink (to take dualink to HDMI) + Lightspace with the LUT inside the ColorBox (about 4.5K more than i budgeted)
-or-
current mon's + wait for the HDlink to work + Lightspace with the LUT inside the BMD...

that fence isn't as painful as it looks...

Author Steve
Scene
#9 | Posted: 4 Jun 2012 07:38 
Hi Dermot, I don't think the Plasma can take LUTs internally, so you would need an external LUT box regardless.

As we know, the HDlink Pro isn't working at the moment... Still waiting for BMD to get back to me with a solution. Nothing from them for a while now (since my previous post above).

The ColorBox is a re-badge of the eeColor box, which I have here on test, and it doesn't work either at the moment. I am working with the manufacturers on fixing this, but not working as needed yet.

The Pluto and Davio LUT boxes do work perfectly

Author Jay Friesen
Mono
#10 | Posted: 5 Jun 2012 01:27 
John_Michaelt: How accurate have you found Resolves internal LUT processing from Lightspace? Last Steve mentioned (months ago), it wasn't handling the LUTs correctly either.

Author Steve
Scene
#11 | Posted: 8 Jun 2012 09:35 
No news fro BMD yet...

But, I was working at a clients yesterday performing calibration, and spent more time looking at the HDlink Pro
Even in 'bypass mode' - no LUT active - the box distorts the image data being passed through it!
This was HDSDI in to HDSDI out, and the problem was easily visible in the shadows using the 'BrightnessCal' image available as part of the Calibration Images download from the Light Illusion website.

The box really is unusable in its present state!


Author Jay Friesen
Mono
#12 | Posted: 8 Jun 2012 16:55 
Steve

I already hate this box. My plasma has no issues with seeing signal direct via HDMI out of the Decklink but I spend more time fighting settings when going through the HDL. If I can get a clean 3D LUT out of Resolve, I'll do away with the box completely. I can host LUTs in Speedgrade now too out my secondary display (not sure if it's 3D yet or not, but the image looks exactly the same as when run through the HDL.

Anyway, I'll run some more tests later. I'm trying to get a project out the door right now.

Author John_Michaelt
Mono
#13 | Posted: 8 Jun 2012 19:12 
We've been able to get very accurate LUTs out of our resolve when in P3 space. However, a caveat. When running in 422 space, I tend to feel like the black levels are slightly off. Fortunately for us this is generally only used for previews and not grading. What I've found critical is getting the projector to put out the most accurate representation of the color space as possible by providing very accurate offset values, especially in the blacks. A hubble doesn't quite read low enough for this, but I've had success with a klienK10 in the bottom end and a PR-655 for the primaries and white patches - or one of the other probes with good off-set values created using the PR-655.

Author John_Michaelt
Mono
#14 | Posted: 8 Jun 2012 19:12 | Edited by: John_Michaelt 
As I contemplate things a bit more - the issue we are seeing reminds me of a bug in smoke when using a LUT on video footage rather than LOG. Smoke assumes LUTs are going to be run on LOG footage, so when using a LUT in the box for display accuracy on 422 footage the LUT is not displayed correctly (video mode as opposed to LOG mode).

I wonder if black magic's LUT integration suffers from a similar problem when in 422 mode as opposed to 444, or maybe in rec709 as opposed to P3 - though the latter seems less likely.

time to experiment.

Author Steve Sherrick
Mono
#15 | Posted: 14 Jun 2012 05:02 
Steve, are you saying these boxes are useless in any scenario, including something like Pomfort LiveGrade? In particular, let's say going from Arri Alexa Log-C into BM HDLink Pro, controlling it with LiveGrade (applying a custom LUT) and feeding monitors on set? Or is this only under specific circumstances?

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