The only thing I can gather from the Pro-DXODR camp's arguments so far, is that we are not really comparing images on a dynamic range basis with DXO's Print DR statistic. We are comparing images on a noisiness basis. Black points and white points and noise may make for a neat and simple definition of DR, but as far as I can gather, DR is not what what is of interest here. The amount of noise, and how that noise presents...explicitly in relation to other images from other sensors...is what is of interest here. If the sole purpose of downscaling a large megapixel image to the size of a smaller megapixel image (or, for that matter, the inverse) is to see which camera is NOISIER, then I have no issue. I don't dispute the necessity of that, although I've never called the improvement in IQ when downsampling a large image to a small image an improvement in dynamic range.
I do dispute that you actually gain
by downscaling a high megapixel image to a smaller size, in a real-world context (as differentiated from a "clean-room" test and compare context, within which normalizing noise for the purposes of subjective IQ comparison DOES make sense). I dispute the simple notion of scaling at all to determine a sensor's
dynamic range, given that the point of having MORE dynamic range is to preserve detail under a wider range of tones, and in the case of digital photography allow that detail to be "recovered" via post-process exposure adjustments. Adjustments that will only really work properly when editing a RAW...which intrinsically cannot be scaled
I'm not sure which information you're talking about "losing". A 40 megapixel camera sampled to 10 megapixels doesn't have less "information" than the image from a 10 megapixel camera.
Still assuming that one is perpetually comparing
camera sensors. Statistical knowledge about a sensor is not necessarily solely useful for the purpose of comparing them
. If I buy a 40mp camera, I have no intention of comparing it to anything else. I have the intention of using it...as a 40mp camera. As such, I want the full stinkin fourty megapixels
, not something less. I also want to know what my camera is capable of natively, unscaled, untainted. I want to know what my 40mp camera can do itself
, not how well it might do thing X in comparison to cameras A, B, and C! In other words, I want to know its intrinsic capabilities, not its relative capabilities.
In that context, scaling my 40mp image DOWN to any size below its native size means a LOSS of information...a true and realized reduction in real image detail that used to exist, and no longer does at 10mp. It also means I have to print at a smaller size, which could be counted as a different kind of loss...but I guess that is beside the point.
The point is to put everyone on the same playing field.
Well, that is one
of the points. It is not the only point of having statistical information about a camera's sensor, as noted above.
If you're looking at a measure in isolation, perhaps the screen score is easier to understand. But if you're comparing sensors with different resolutions, you need to make some adjustment to account for the fact that the higher resolution sensor has more pixels and therefore more photographic detail.
Agreed. From the standpoint of normalizing noise to compare how noisy one sensor is vs. another (which is what I gather the DXO Print DR statistic is all about based on the arguments from you an LTRLI), then sure, you should be normalizing image size. I've argued that myself in the past, although I've never called the change in noise an improvement in dynamic range before, but thats probably simply because I define dynamic range a bit differently than DXO (although admittedly in a different context as well...that of "real-world digital RAW post-processing" where most of us photographers actually live, so it is not necessarily to say DXO's definition is wrong...just meant for a different context.) I've simply called downscaling for the sake of comparing noise the normalization of noise. Something along the lines of "Normalized IQ Score" would be a much better term for this than "Print DR", though, as it really has nothing whatsoever
to do with print
. Print, paper, inks, ink density, lighting, etc. make actual print so far removed from what DXO is actually trying to demonstrate with this statistic that they should really rename "Print DR" to something less controversial, and something more meaningful.
I believe Imatest, technically a competitor to some of DXO's other business I guess, named their score for roughly the same thing accordingly: SQF, or Subjective Quality Factor. I believe DXO "Print" statistics are really another form of Kodak's SQF. I believe Imatest got the name right for IQ measurements
as well...they simply call it MTF, rather than something more obscure like "Screen".
I think the point about only 6 stops of dynamic range being available for paper is a bit of a digression -- if you don't need more than 6 or maybe 8 stops for some safety margin, why would you care about dynamic range ? Any modern DSLR has more than that.
Sorry, but it's been my entire point all along, as my complaint is with the fact that DXO sells "Print DR" as something it is not, by its very name, even. Or, at the very least, they explain their modeling system in a way that many people have incorrectly interpreted, as people are inevitably going to think "ink on paper" when they hear the word "print". I also believe the heavily weighted use of "Print DR", if it is weighted rather than purely a measured statistic (I can't find the page right now that describes how and where DXO adds "bonus points") in their scoring mechanism is extremely misleading.
Additionally, the same statistics, assuming they are accurate enough in the broader context (which in the case of Print DR, it is not...it has a very narrow and specific usage solely in the context of comparing sensors scored by DXO), can be used to learn about what a sensor offers in and of itself outside of any context of comparison. Such as how much exposure latitude do I REALLY, ACTUALLY have when I am pushing shadows around with my RAW images in a RAW editor
. Or, say, what the sensor offers when ACTUALLY PRINTING IT AT NATIVE SIZE (so no scaling or averaging of any kind)? DXO's Print DR statistic is insufficient to answer those questions, while Screen DR, effectively being hardware measurements as they are otherwise untainted by software, IS sufficient to answer those questions. Hence my reliance on Screen DR to describe intrinsic capabilities in contexts where relative capabilities are meaningless.
Perhaps my complaint is simply with how DXO sells, names, uses, and refers to their statistics. If they had used the terms "MTF" or "Measurements" and "SQF" in place of "Screen" and "Print" respectively, I probably would have never had a problem. Labeling their overall dynamic range score as the "Landscape" score (immediately putting it in a context where actual camera USERS might literally try to photograph scenes with more than 14 stops of real-world dynamic range), then stuffing in a number that (potentially greatly) inflates the intrinsic hardware capabilities, is excessively misleading. At the very least, SQF is explicitly defined as a way to produce normalized comparisons for the purpose of accounting for "viewer experience"...a subjective factor, which sounds a lot like what DXO's "Print" scores are supposed to be. SQF has also been shown to be an ideal way to statistically measure image IQ produced by digital sensors (when, ironically, it wasn't so ideal for measuring IQ from film), one which has never risen so much ire as DXO's "Print DR" statistic.