Pixel density revisited

Started Oct 22, 2008 | Discussions thread
DMillier Forum Pro • Posts: 20,895
Re: Pixel density revisited

It's difficult isn't it.

For me, printed output is the goal, so the quality of the prints at different sizes is important. DPReview sometimes comment on whether differences are visible in prints but it tends to be vague like "only visible in very large prints".

I would find an assessment of the test images printed to some arbitrary size (eg A3, A2 etc) useful. But to evidence this would require scanning sections of the print and there would inevitably be complaints about the methods/equipment used.

Likewise, if the noise patches were all scaled to a common size, there would be arguments about the re-sampling method etc.

I also suspect, that one of the effects of such tests would be to show that the output from most modern cameras is very similar given appropriate settings. And a review site whose message was predominately "most cameras of similar spec give siilmilar results" would get boring fast....

bobn2 wrote:

Phil Askey wrote:

I think a 30+ page review correctly qualifies any statement about
pixel density and noise. Where is this reverse evidence?

It could be any length, but if it didn't contain any statements
relating noise content to final output size, it wouldn't be
qualified, would it? I've read through it quite carefully, and I
can't find any pointer there that would help me understand the
relative noise between the cameras for usual output sizes. There are
a lot of statements about how noisy the A900 is, but all related to
per pixel noise.
As for the evidence, Emil has pointed you to a post of his, there's a
long series of posts which you didn't follow, but did discuss and
present the evidence in some detail, there's John Sheehy's
demonstration under the title 'the joy of pixel density' , and
finally there have been extensive discussions of the physics behind
it, which back up the position that in theory there is no causal link
between pixel density and final image noise content at any given
image size (with the caveat that there are noise effects such as
random telegraph noise, which come into play at very small
geometries). These discussions included a number of people who are
research physicists (not me, I hasten to add), and included Eric
Fossum.
I'm not really asking you to go back on your testing methodology
completely, it just seems to me that including a set of equal sized
crops from a given proportion of the frame (resized using a sensible
resampling method, there are plenty here who could advise) would be
much more helpful for people to assess the likely image quality from
any camera, and to make comparisons between cameras of different
pixel densities and sensor sizes. Do it in addition to the 100% crops
if you like (and please, in RAW), but it would improve the reviews
still further. Similarly, the crops from the 'bottle' scene are
difficult to make judgments from when they are presented at vastly
different output sizes.

bobn2 wrote:

These statements on noise and pixel density need to be qualified. The
message that people are getting from statements of this sort is that
increasing pixel density reduces image quality in an absolute way,
and there is no evidence to support that, rather the reverse, in fact.

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