Lightroom's 4 color "spaces"

Question

I’m working on designing an advanced photography course. This course makes use of Lightroom and Photoshop in the photographic workflow.
I’m learning and researching myself as I go along, and I feel I have reached a ceiling on what I can work out from the sources at my disposal thus far.
So I am turning here for help.
I am trying to clarify how tones and colours are affected from the actual scene through to the printed page. This might seem like overkill to some. However, there is a lot of misunderstanding and confusion, not to mention heated discussions amongst photographers about these issues. I’m experimenting with metering and colour / tone targets and my calculations are only meaningful if I understand how tones and colours are affected at every stage of the workflow.
Here’s how I understand it:
There are 4 (sort of) Colour “spaces” in Develop where a real-time dynamic preview of an image is rendered
1.       The “viewing space” (ProPhotoRGB Chromaticity co-ordinates, sRGB gamma)
2.       The “computational space” (ProPhotoRGB chromaticity co-ordinates, linear gamma – “MelissaRGB”)
(Martin Evening’s Lightroom 3 book published by Adobe press - Appendix B, section on color space page 628-632)
Below that, things get a little fuzzy. According to Jeff Schewe (Real World Camera RAW for CS5, page 32) there is a sort of
3.            “Native Camera Space” and of course there is the
4.            RAW data in the file on disk.
So to generate the dynamically rendered preview, the image goes through the four “layers” as follows (from bottom to top). This is almost certainly flawed, but one has to start somewhere when trying to work things out :-)
1. The RAW file is read from disk. Colorimetric interpretation is performed using a camera profile (e.g. Adobe Standard for whatever camera it is you are using). This process puts the image data into “Native camera space” (“Plotted” onto CIE XYZ with D50 white point)
2. In “Native camera space, the scene white balance (as selected by user, guessed by Lightroom or reported by camera) as well as additional camera calibration panel matrix tweaks “informs” the colorimetric conversion into Lightroom’s “computational space” e.g. Melissa RGB. The colorimetric definition of camera RGB primaries and white is re-DEFINED. The demosaicing as well as chromatic aberration corrections are performed in “native camera space”
3. Almost all image processing calculations occur computationally in the  “MelissaRGB Lightroom computational space”
4. What is displayed on the screen, however, has an sRGB tone curve applied. This represents the “viewing” space. The histogram is generated from this and the RGB colour percentage readouts are generated from this as well. In addition, some slider controls from user input are weighted back through the tone curve into the computational space below.
Could someone from Adobe kindly help me to clarify the steps? Eric are you reading this? :-)
Thanks in advance

Answer 1

Sandy - Thanks for the link. The spreadsheets you posted on your site is quite helpful.
Jao – I think what you said goes to the heart of what I am trying to achieve here: “Photograph a grey target at the exact same exposure with the exact same lighting but with different cameras and you'll end up with different values in the raw files” Which is why I encourage photographers to experiment with their cameras in order to understand exactly how the camera will respond in the heat of a real shoot. Set up a scene; take a picture, open in Lightroom. What is clipped and why? Use a reflective spot meter. Repeat. Use a hand held incident meter. Repeat. How much can you reliably recover? Are you happy with what your meter considers the mid-point (and what you set your exposure for on the camera) or do you need to compensate? Just how much latitude do you have between what your camera histogram shows as a blown out highlight and what Lightroom shows as a blown out highlight. This relates to tone. I could go on with more examples, but by now, I am (hopefully) making more sense.
I’m merely trying to clarify that which is already public in order to form a coherent mental picture. And by mental picture I do not mean an accurate representation of the minutiae and maths involved. Think of a subway map. It represents a bird’s eye view of a transportation system in a logical fashion, yet it bears almost no resemblance to the cartographical reality of the physical topography. I really don’t care where the tunnels go, how they were dug, how they are maintained or where they twist and turn. What I AM looking for is a logical (not physical) map. This map tells me where the different lines begin and end, and where I can change from one line to the other. The most important quality of the map as a whole is that it provides context. You can tell, at a glance, how different lines interact with each other and even how it links to other entities such as bus stations or public landmarks.
As many have rightfully pointed out, I should not have to care about the maths/secret sauce/internal calculations. And I don’t. In addition, I am a very happy Lightroom user and I am very comfortable using it. I know what a user needs to know to get his picture from A to B. There is no shortage of information on how to accomplish that.
It might help if I illustrate what I am trying to do below:
Please excuse the low resolution, the maximum height allowed for upload is 600 pixels. The picture below goes on the bottom left of the "layer" picture above.
Even though there are certainly many mistakes in my diagram, this is a helpful visualisation. I derived this diagram from publicly available information. As the subway map, this is a logical (not physical) representation that provides context in a visual form. With a little help from people like Eric I am sure I can correct and expand it. The net result is an enhanced understanding of Lightroom and ACR and where it fits into the photographic process, both in terms of tone and colour.
I am not posting the entire chart here since I am not even certain that a 4 “layered” representation is an appropriate logical representation. I posted the spine of the chart with the 4 “layers” and one part that elaborates on the colorimetric interpretation between the two bottom layers. Comments and corrections are welcomed. And I am convinced that this can be accomplished without divulging anything confidential.