How does no profile option work in RT?

Software RawTherapee
1

RT has an option of “no profile” when rendering a raw file.
But what’s happening when there is no profile during rendering a raw file ?
At least a certain color matrix must be applied as it is difficult for me to imagine a rendering without matrix.
Yes, a rendered image under no profile seems to be far away from one with profile, but at the same time not too much far away from the latter.
Can anyone tell me how the story goes ?

2

http://rawpedia.rawtherapee.com/Color_Management#No_Profile
http://rawpedia.rawtherapee.com/Color_Management_addon#Initial_raw_processing_before_RGB_conversion

3

Morgan

Thanks for links.

But I don’t really understand what the following sentence means: No Profile: Bypasses input color profile. For raw files you will see the camera’s native RGB color, just demosaiced and white-balanced. Color Management - RawPedia

Can I correctly translate it into like this: no profile is equal to a matrix of which each entry is 1 ?

4

I don’t think so. But @ilias_giarimis most likely can give the correct answer!

Ingo

5

Not each entry … only the three elements on the diagonal are 1, all others are 0.

This is then multplied by the XYZ_to_working_space matrix … so you will see differences if you change working space. This is the reason it looks as [quote=“PCU2, post:1, topic:3265”]
not too much far away from the latter
[/quote]

This is my understanfing … I am not sure about this, I am not a color expert … I 'd really like an explanation by @jdc who knows the RT color management internals …

6

heckflosse, ilias

Thanks for your interventions respectively.

I am sorry for my bad understanding in maths, but I had wanted to say that “no profile” may be equal to a neutral matrix that changes nothing.

With profiles including matrix being designed for color management in general, can I assume that rendering without profiles is more straightforward and accurate than with profiles if you want to compare nature or character of the sensor/raw of a digital camera with another ?

7

No profile is “no profile” !
That is to say, that there is no ICC profile neither DCP profile, nor matrix, or if you prefer a matrix that does nothing with a 1 on the diagonal and 0 elsewhere.
The interest in photography is almost zero, because we have an image with all the shortcomings of the original sensor

On the other hand this has two interests:

  1. show the original image without correction (pedagogy)
  2. allow to develop TIF files, to make ICC profiles, DCP profile: But here we enter another debate, where the role played by the target is very important.
  • the colorchecker 24 is for me, not a good choice, or a default choice because we do not have anything else.
  • In fact, RT is set to Prophoto (input) by default, while the colorchecker 24 hardly exceeds the gamut of sRGB, it is obvious that there is a “trick”. The profile generator will extrapolate considerably, with enormous errors. The solution is to use a target with a wider gamut - which can go in some cases until Widegamut…But as I said we are entering another world!
    :slight_smile:
8

RawPedia updated.

9

jdc, Morgan

Many thanks for your clarification respectively.
I find myself far clearer on the topic.
Thank you again.
As far as producing dcp profiles, Adobe’s DNG profile editor has been my unsatisfactory friend.
It’s easy to use while inaccurate and heavily dependent on a precedent profile on the basis of which a new one is to set up.
I hope to have a software that can easily adjust dcp profiles from no-profile images.