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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

"Black Sun" Revisited - RAW Processing Bug?

Jeff Kilgroe

Jeff Kilgroe

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I'm posting this up quick while I'm thinking of it. The two images here don't illustrate this well at all. So I'll round up some better images later...

Working with my footage that shows the infamous "black sun" or dark grey / purple spot in bright flares, I'm able to recover information out of that dark spot. It behaves just like an error with some sort of clipping threshold. The threshold seems to be defined or influenced in relation to which ASA the RAW image is being "exposed" for. A higher ASA value appears to raise the threshold, lower ASA values lower it.

The "black sun" or sensor protect or whatever we call it, appears to be pixels that have exposure values extending beyond this limit or threshold. At this limit, instead of simply being left at a 100% luma value, it's as if they're being rolled-over to zero. Increasing the ASA seems to change that upper limit and much of the dark or black pixel data no longer "rolls over" (assuming that is what is happening) and it remains white or at a 100% luma value.

So I'm thinking that the "black sun" is completely fixable and may even be a bug in how the camera, REDCINE and RED Alert all interpret the RAW data as the anomaly is present in the camera outputs as well the software tools.

This image is a 1:1 crop showing a flare with slight "sensor protect" artifacting. Shot / exposed for ASA 320.
535_1203733736.jpg


The exact same frame from the same R3D file, but exposed for ASA 400. The "sensor protect" artifacting has disappeared.
535_1203733784.jpg
 
It's a sensor thing, not a processing thing.

Graeme
 
I leave that kind of thing to the sensor gurus at RED.

Graeme
 
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Thanks for the response, Graeme. I remain hopeful that a solution will be found. At least I'm finding that it's pretty easy to compensate for the effect, or even eliminate it, in REDCINE. Severe instances of the anomaly will probably have to be dealt with by tracking and removal in other software.
 
We are working to fix it but for now pushing up the highlights a bit will correct for the pink sun.
 
well.. I'm no sure it's a CMOS issue, maybe the purple area showed on the picture is.. but what I get si not...

Because the If I render to DPX files purple pixels are gone... but the effect it's different.. mine look like real dead purple pixels..maybe is not the same issue..
Picture9.png
 
JJRecort, I need to see that R3D file from that shot to debug, and what version you're using to get that error.

Graeme
 
Thanks Graeme, I will upload to my FTP the smaller R3D file I have where the problem appears.

Shots was done on Studio, at 3200K - 320ASA - 2K - 50 and 100 fps
Can not tell now if we where using build 13 or 15 (should ask to cam operator)
Now with the experience I think we shot a little bit overexposed.

All is up to date on the REDCODE; REDCINE, REDALERT software side.

I'm my case I have tried in two Macpros

one Macpro (prior to JAN08) with 10.4.11 it's happening always, whatever you use REDAlert, Crimson, or REDCine, whatever Codec it's chosen. Only rendereing DPX files with REDALERT it's working fine.

On my other Macpro (post jan08) I'm having the same issue but only if I render with RedCine.. the weird purple pixels are appearing on some parts of my shots... If I manually render with redalert, or Crimson shots are rendered okay...

BTW.. we meet in person the last -manufacturer's -day at IBC.. I was one of the hundreds of skeptics not believing how to fit 4K on a CF....

Cheers! (and thanks!)

Come to you later on with the FTP details.
 
Jordi, thanks! I could do we seeing the R3D file to reproduce the effect here. I've seen that kind of thing before in an alpha build of the software, but I thought we'd fixed it. I'm off to NAB now, but will be able to look at it once I get there I hope.

Graeme
 
Wow! I didn't expect tp find you awake at this time..

I'm uploading a file... the shortest is 880 MB, sorry for that..
There is any way to just cut a R3D file without processing it? this way I can upload a smaller file.

I have opened this file, and just rendered to Prores in REDCINE.. and now, in this test, the rendered file have purple (a littlebit more blue this time) on all the frame... not only on specific areas..

File is uploading... upon finished I will test the link and post-it here..

I still don't know if I'm going to NAB this year.. I have another Shooting+Post next week... so, unless this shooting is delayed it's difficult to me attend this year :(

Cheers!
 
Hi Graeme... just landed in Vegas... could imagine you're so busy with the booth...

here are the links...

http://www.deunido.com/media/PurplePixels.R3D.zip

this is the original R3D file (one of them)

this is the Processed file with REDCine one week ago

http://www.deunido.com/media/PurplePixels.mov

this is the file processed yesterday

http://www.deunido.com/media/BluePixels.mov

what changed? the Graphics Card.. this week I swapped the ATI2600XT for a nVIDIA 8800GT.

but, on the othe macpro, with Tiger and QT 4.3 has been happening from day one the same way blue pixels all over the frame.

we have been showing the shoots to othe people with some experience with the RED and they said to us that we had a problem with the setup of the camera.. it's not only the problem of the pixels.. everything seems to have a very tigth margin of operation, I mean: as soon you try to increase ligths a little bit.. low ligths appear to have a lot of noise.. so the only way to have some kind of rigth image is keeping the Gamma linear (1.0) and drop down the low ligths... even doing that, chroma masks (we used Keyligth in AE and Primatte) are very dirty with a LOT of noise... If you take any image and try to pull up the ligth to higher levels, a lot of banding and artifacs appear...

I'm thinking that ServiceVision, the rental company installed the Build 15 (when it was beta) and did not recalibrate the Black Shading... could be that? but they're still saying the Camera was ok.

thanks in advance! and have a good NAB!
 
What's funny about this is that someday someone will make an NLE plugin to make your footage mimic that "early digital cinema cam" purple highlight look for retro purposes.
 
Have you tried on latest Redcine? I'm not seeing the issues on my dev tools here.

Graeme
 
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