#apertus IRC Channel Logs

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wb troy_s!

Bertl: First answer, a Bradford weighted 3x3 transform works for WB.

so the gamma correction happens after that?

Yes.

Bertl: See http://ninedegreesbelow.com/photography/linear-gamma-blur-normal-blend.html for the blending issue

Bertl: So I believe all Bradford etc. manipulations (including all transform between RGB color spaces) must be on linearized data.

yes, at least for the CMV12K sensor it should and seems to be

that was the 'should' part :)

gotcha

but setting white point should be a simple 3x3 Bradford with the primaries of the sensor known and blended into that matrix.

Bertl: Currently there is no TRC, so that would be something you might add for grading purposes - starting at a Cineon Log for example. Or Josh Pines... a sort of base starting point for those graders who prefer a curved start.

DPX?

(little like Canon does it)

rexbron: Sorry but DNG stinks.

rexbron: Simply zero uptake and not as versatile.

so let's adjust the order of events to 'our' case

i.e. we start with the 'linear (really) raw data' from the sensor

rexbron: And you also need a way to specify a TRC and DPX does that well. Exactly my point.

troy_s: also cDNG has really good uptake. Resolve, Premier Pro, After Effects and Nike believe

rexbron: My primary gripe is really implementation. The lack of penetration and a go-to library doesn't help.

troy_s: on the foss side? It's tiff

Sometimes gamma, sometimes a two part algo like 709 or sRGB

troy_s: as for a goto library, dcraw supports it iirc

rexbron: As an aside... I am not exactly opposed to DNG.

Bertl: Probably metadata if we can find a defacto example existing.

rexbron: You aware of any app that interprets the DNG metadata for WB and applies a transform?

troy_s: Resolve can definately do that. I'm pretty certain any app that uses DCraw supports it as well

it's why you can use adobe lightroom with BMCC footage

rexbron: God that sounds joyful - NOT. LOL.

no, I'm currently interested in processing the sensor data and generating HDMI output :)

rexbron: Not many are scene referred. Hell not Resolve methinks as it doesn't really support CDL aside from ingestion right?

HD-SDI ftw lol

Bertl: Was more speaking of a reference bit of kit to deal with the files.

well, HDMI with a weird 4:2:2 RGB mode is all we have on the axiom alpha prototype

Bertl: Fair. After all any Bayer sensor is 4:2:2 native.

rexbron: No interface for CDL. Was always LGG, no?

Bertl: The sensor is 4:2:2

Obviously for post processing it is meh, but I would think that is all after a dum

troy_s: CDL also assumes display refered rec709

But I may need to read the spec again.

err

How odd.

Although I think that makes sense actually

Because you sort of need a white calc for sat.

Bertl: How goes engineering?

good but slow for my taste, but it is rather complicated

so my idea of post processing atm looks like this:

Bertl, troy_s: keep in mind that Aaton was bankrupted and Blackmagic design is pulling it's hair out over differences in the chips when moving to production scale fabs

run the r,g,b data from the sensor through a generic matrix (if required) and through a lookup table per channel

troy_s: that is what DNG is. It's TIFF for bayer raw images

because HDMI is probably not happy with the linear color data

Bertl: Gotcha. I see the point. Should be a simple matrix (single) with white point transform via Bradford (two matrices boiled into one)

LOL

we probably need a lookup for gamma correction as well

Bertl: It would look like this:

1) RGB to XYZ via custom matrix

3) XYZ to 709

5) HDMI

okay, the LUT is what I meant, and we need it per channel or just a single for all channels (R,G,B)?

TRC would apply to all channels

Bertl: from what I understand, those matrixes are created under CIE illumenant A and CIE D65 and anything inbetween has been interpolated

and I think the best way to implement the matrix part is a 9-way lookup, mul and add

Bertl: That is the sound of higher thinking than mine shooting right over my head.

well, look at it like this:

this results in a0*x + a1*y + a2*z, b0*x + b1*y + b2*z ...

similar for a1*y ... b0*x ...

gotcha

Bertl: Bradford transform should be simple for you to figure out... it is sort of a transform to yet another space actually

and the LUT values can be calculated from linux userspace

(which allows for some flexibility)

Bertl: So what is your current engineering roadblock?

yes, the zynq features two hardened arm cores

we have our own kernel and userspace running there :)

Was there a pissing match between Axiom and Elphel?

fun...

(the pissing contest :)

PL is the acronym I use for the FPGA part (contrasting PS for the ARM cores :)

we could actually stream full 4k at 25 or 30 frames into memory already

Wow. Impressive.

we currently use the nikon-f lens mount adapter

https://www.apertus.org/sites/default/files/alpha-lensmount02.jpg

I too think this solution was kept, yes

Reference standard is PL, and anyone aspiring to create high quality images will be borrowing PL mounted lenses.

well, as soon as there is an open PL lens mount, it can be used

Bertl: I only said that it seemed silly because it lacked the context of who this whole project is aimed at.

That means that for lower end, the Nikon makes perfectly good sense. As soon as you are talking low budget though, you are also likely talking pulling favors including borrowing lenses, which is very common.

well, I haven't been around when the nikon f-mount was created, and I guess you haven't either

as I said, if you want to see the PL-mount for the prototype, you just need to find somebody to do the 3D design for it (and figure out how to get the mechanical part working)

don't forget, we are working on the prototype for free

It is a pressure slip

needs some kind of pressure, usually applied by a spring :)

i.e. the tube and bottom part should be quite similar, maybe the tube length needs adjusting but that's probably it

I think it is dovetail mechanics

very low tech

for example, we use the mechanical locking part from a camera body (for the prototype)

shimming will be a nightmare

Yes. To get backfocus to align infinity.

well, that's actually trivial, as we can cut the spacer with a laser cutter

)

morning everyone!

hello!

wb dmj_nova!

I miss anything?

evening se6astian!

hey mars_! how's going?

but it was a long day and so far away from home

oww :)

oh hello, so many new people recently

sorry gotta go, time for bed

time to catch up then