Hm, I’m not sure I’d agree. Well, I totally agree that
however I’d very much disagree that
I think @Troy_James_Sobotka put it quite well with this quote
[Typically], for non spectral based stimulus, the peak brightness range will rest along the achromatic axis of a medium. Chroma laden primaries or paints will almost always achieve a lower “brightness” at maximal emission / reflectance of stimulus.
In terms of the Monet, the sun is not white and yet it appears bright, surely… in reference to the rest of the image, as @Derek said. Yet, it doesn’t appear as bright as the sun would have appeared had we been standing next to him as he painted it. He’s made the decision that this isn’t important for him – he cares more about evoking the emotion that the fully chroma laden color does than about making our eye see the sun as brighter. There’s nothing (if we get it right) preventing someone from making the same choice even with a DRT that does use a ‘path to white’ – if the artist chooses to make the same tradeoff, there’s nothing stopping them from grading with a Look that severely caps the luminance of the sun down to a level that will be able to be directly displayed on their reference display (in which case the DRT shouldn’t affect its chroma, unless later retargeted on a less capable display).
Actually, this segues into a topic that I’ve been trying to wrap my head around enough to post about it in a comprehensible way, which is the topic of how to evaluate transforms.
Something that I think has been a little bit looked over as of yet has been the casual nature by which we’ve evaluated the proposed methods… basically it’s just been a matter of taking some raw scene-referred footage and passing it through and then evaluating the subjective/preceived ‘beauty’ of the result. I think that this is actually quite an ill-formed method of comparison/evaluation though. Troy posted a tweet thread today that I’ll ‘unroll’ here as it directly relates and finally connected the dots to make this fully comprehended in my brain:
When we have a stimulus encoded in data, no matter what we do, we are going to have that stimulus rendered in a medium like a display. We have no options; it will always come out as something. The idea that we can somehow ignore the limitations of the medium is what yields broken looking imagery. We must, at all times, start with the medium and work backwards to form an image. Why? Because again, whether we like it or not, every single stimulus encoded piece of data will be forced out as something. Either we can control that, and form it into an image, or we can ignore it and it will be formed into an image for us. This is not optional.
What does this mean? Well, it means that in evaluation we need a “ground truth” which is itself a fully formed image… i.e. an image which we don’t feed through our DRT but to which we can compare the fully-formed image output of the DRT. I’m honestly not sure of the best way to create this ground truth reference, though, which is an important piece of the puzzle. But the point, as said by Troy, is that this ‘reference formation process’ is a non-optional piece of the picture. By ignoring it, as we are now, we’re just leaving it up to chance, but it’s still ‘happening’–“doing nothing” is still a rendering transform, just one that doesn’t have a well defined output… so we should instead actually think about and actively form that process instead.
This is contextual, put your display outside and it will look like very disappointing! 
