Re: [Openexr-devel] Query: Image Based Lighting and HDRI-enabled cameras

[Anders Dahnielson]

> I thought about mentioning log space sampling.  I'd forgotten that
> the 10 bit formats used for recording to film are log.  That does
> of course make a significant difference, although as you wrote it
> requires a linear ADC and conversion.  If one is recording raw one
> should just take what the imager offers and worry about converting
> that into something more permanent offline, rather than in real-
> time.  It has to cost less to use a gen-purp box than to engineer
> such stuff into the embedded system on the camera....

Yes. Converting 12-bit linear to 10-bit log will always discard
information that is important when dealing with HDRI work (for the same
reason OpenEXR preserve values above 1.0f and below 0.0f).

The main purpose for log convertion in our design is simulation of D log
E transfer curves in addition to the benefit of fewer bytes to store and
transfer. Since we're currently at the desig stage we may bump up the
ADC from 12-bit to 14-bit (16-bit) linear and convert to 12-bit log. But
that depend on the CCD output voltage sensitivity and ADC cost.

The log convertion itself isn't very complicated since LUTs can be
utilized. For 12-bit linear to 10-bit log a 5 KB table of 4096 10-bit
values is sufficient.


> So it is wider than 35mm film's framesize.  Perhaps the edges
> provide same dark pixels to help measure the noise floor?  Or
> do the MP cameras & lenses cast light on the filmstrip's
> sprocket holes?

That depend on the lense and focal length (some may cause vignetting)
but in general most lenses give enough coverage.


> NB that they do offer raw images at 16 bit/pixel linear bayer
> pattern at a whopping 3216 Mbit/s over 4 fibre infiniband
> pipes.  I think I'd prefer 4 gigabit ethernet pipes myself.

Our camera design will output 2048x1536 pixels, 10-bit log (may change)
Bayer pattern, lossless compression over one IEEE 1394b (a.k.a FireWire
800) link and have a variable frame rate of 0-50 fps.


> Also, if the interpolation is done in the camera, that jumps
> to 9648 Mbit/s and requires (lossless) compression to fit in
> 4 infiniband pipes.

I always tought interpolation in camera was a stupid idea. ;)
It's like having a small data set and then padding it instead of
compressing it.

--
Anders Dahnielson
<address@hidden>

GnuPG 1024D/D424211B 8FDC 38E7 D8E9 67AE 85F4  F2A1 D71D 7FCE D424 211B

"When an actor comes to me and wants to discuss his character, I say,
'It's in the script.' If he says, 'But what's my motivation?' I say,
'Your salary.'" 
    -- Alfred Hitchcock

signature.asc
Description: PGP signature