Help with DNG Spec Matrices

[Adam Bonn]

Hi everyone,

I was hoping to get some advice..

The Premise

I'd like to create forwarding matrices for use with the 'embedded' profiles that are included with cameras that natively shoot DNGs.

My Problem

I've read (and re-re-re-re-read!!) the adobe DNG spec document and I just can't get my head round what I need to do...

I think I'm ok with the maths....

I'm lead to believe that the Forward Matrices (hereon in 'FM' for brevity) can be calculated using the data found in the Colour Matrices (CMs)

The maths for this seems fairly simple....

From Adobe:

First, invert the XYZtoCamera matrix.

CameraToXYZ = Inverse (XYZtoCamera)

Second, the white balanced transform is computed
CameraToXYZ_D50 = CA * CameraToXYZ

(CA is an equation found on Bruce Lindbloom's site)

I'm using excel to perform the maths...

(MINVERSE to inverse matrices and MMULT to multiple them)

I'm not managing to get values that work (hell I'm not even managing to get values that look right!!)

• I'm fairly sure that my first problem is the data I'm using to base the XYZtoCamera inversion on (but don't take my word for it !!)
• My second problem is that I'm unsure if the DNG tag 'AsShotNeutral' is an XYZ value, or a RAW RGB one (I can calculate a known XYZ value first into XY, then CCT)
• Thirdly! It seems that I have to create a single CM, via interpolating CM1 and CM2 using a combination of the CCTs of CM 1 & 2 (A and D65) combined with the CCT of the scene as shot

Originally I thought that this was simply the CMs inversed, but I guess not....

I was hoping that someone here could help walk me through it....

There are a few blogs etc that detail this process, however they start from a base colour target and build a profile from scratch...typically using one CM and one FM. what I want to do is piggyback from the incumbent DNG existing CMs

Thanks in advance for any help

Oh and... I've asked this in a couple of other places and generally folks ask why.

Well IMHO the native colours of DNG are nicer than the sanitised look of a modern LR/ACR dcp file, but the bare bones embedded profiles struggle at sub-D50 illuminate levels. Also going forward I wish to colour calibrate my cameras, and I'd like to produce profiles that follow the DNG spec as closely as possible.

 

[ecoleman]

I lost you at “Hi everyone”

 

[realspeed]

I think he wants to take a photo' What I do is switch on the camera and point it towards what i want to photograph. Next step is tricky, I put my index finger on the " take photo shutter button" and press down. Bit technical I know but with practise it becomes easier

 

[ancient_mariner]

From the look of things, the OP wants to ensure his images have a neutral processing as is found in.dng files, carried forward by the camera profile, and is presumably writing software to manage this. Sorry not to be able to help.

There was once a time when one might prefer to be thought possibly ignorant, rather than open ones mouth and remove all doubt. [emoji6]

 

[Adam Bonn]

From the look of things, the OP wants to ensure his images have a neutral processing as is found in.dng files, carried forward by the camera profile, and is presumably writing software to manage this. Sorry not to be able to help.

more or less.

I want to use existing software, but with my own interpretation of neutral processing

 

[Adam Bonn]

Wow my brain hurts, what does any of that even mean???

Your camera shoots raw data. Raw data has to go through various transformation steps to be a photo.

When you open a raw in (say) LR (or whatever) many of these steps have happened already.

That was a list of some of the steps that have happened already before the RAW file is displayed in your raw editor (although that's the steps for ACR/LR, C1 etc will be different)