[HDR-photo] Re: HDR-photo Digest, Vol 6, Issue 1

[Justin Johnson]

>
> The "practical" bottom line: try to eliminate any unwanted effects of
> WB by keeping it consistent, and working within its limitations. You
> still have wiggle room there, but by combining multiple exposures
> into your HDRI file (as opposed to using a single input RAW) you can
> reduce relative "color errors" that the WB might impose when it
> shifts the RAW input to one end of the spectrum or another.

Our goal with the HDRIs here is to use them to do image based  
lighting in our 3d renders.  Ideally, we would be able to match white  
balance of the HDRI to the Cineon perfectly.

However, exact science seems out of reach without the ability to have  
control over the way the film is scanned.  There is color timing  
applied during the scanning process seems to vary wildly.

To get the HDRIs and film scans to match perfectly, a color/gray  
scale chart could be filmed at the head of each shot and used to  
create a LUT that could be applied to each raw capture.   All of this  
seems to be impractical for the result obtained.

Does anyone know of a way to match HDR to film scans with a simpler  
method?


>
> -Mark Banas
>
> P.S. If Chad D. is still at Luma, tell him I say "howdy."
>
>


He is still here. I let him know you said hi. He said you were a big  
help with our HDRI rig. Thank you very much.





>
> You can do this with DCRAW. Using DCRAW and the flag "-d" or "-D" will
> output the grayscale sensor data as a .PGM file. The problem is that
> it's not only grayscale, it's also mosaiced/has a grid pattern. I made
> a demonstration image, and it is here:
>
> http://danreetz.com/for_HDR-photo/output_test_DSC3445.jpg (be sure  
> to zoom 100%)
>



That really opens my mind up to how RAW files are stored..  I knew  
that my question would be answered with an in-depth explanation of  
things, I just had no idea how far that explanation would go. Thanks  
to everyone for this information.. It's immensely valuable.







>
> One could go even further by recording in the metadata of the HDR  
> image the
> color matrix of the camera (or even two color matrices depending on  
> two
> different calibration illuminants like the DNG format allows) in  
> addition to
> the white balance information. The conversion from camera to output  
> color
> space would then entirely be controlled -and adjustable- in the  
> tone mapping step.
>


One possible feature could be a setting to give the best guess white  
balance to match a typical film scan converted to linear.



Thanks
Justin
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