more pixels are better!

Started Dec 14, 2008 | Discussions thread
bobn2
bobn2 Forum Pro • Posts: 70,345
Re: More pixels are not necessarily better...

DaSigmaGuy wrote:

bobn2 wrote:

DaSigmaGuy wrote:

Iforgetwhat8was4 wrote:

or are they?

Could someone try to give a clear but comprehensive explanation of
why more Mp doesn't improve IQ?

Given a fixed sensor size the camera with higher "resolution" will
produce a physically larger image than one with lower "resolution"
but one that is noisier and has reduced image quality, because
smaller photosites equal more noise, fact.

Brave man, wading into the discussion without bothering to read it,
and offering a contentious (and wrong) view.

Yes, you are.

Not me, I'm offering a contentious but right view.

Statement 1, wrong. The file produced by a higher "resolution" camera
is not physically larger. If by higher resolution you mean higher
pixel count (they are not the same thing, since a camera could have
higher resolution but a smaller sensor and thus have fewer pixels)
then the physical size of the image is dictated only by the output
medium.

Oh dear...I guess I'll have to put it a bit more simply for you...
"Given a fixed size sensor" means the sensor is the same size in both
the high resolution and the lower resolution camera.
The output image size is therefore determined purely by how many
pixels a sensor has,

Output image size has nothing to do with how many pixels a sensor has. You don't seem to have grasped this.

meaning for all practical purposes pixel count,
resolution and image size are one and the same thing.

And therefore you've got this wrong. Very wrong.

As an example, lets assume you have a FF sized sensor (36mmx24mm) in
both cameras being tested but one has a resolution of 12mp and the
other a resolution of 20mp.
The image size produced by the 12mp FF sensor is something like
4000x3000 pixels (Perhaps not exactly in that ratio though because FF
might not be exactly 4:3 format(?), but good enough to use as an
example.) The image size produced by the 20mp FF sensor on the other
hand is something like 5000x4000 pixels..Nearly 17% larger from the
same sized sensor.

Those are not image sizes, they are pixel counts written a different way. Size has to do with spatial dimensions, the things you measure in metres, feet or inches, not counts.

Which will produce the better QUALITY images...The one with the
larger photosites, ie: the 12mp camera.
Which can capture more detail...Obviously its the 20mp camera but
because it has smaller photosites its pixels are a lot noisier.

It's pixels are, but its images aren't. Now there's a paradox for you. You could try to work it out.

Well then why do need to ask?

Fishing to catch chumps who'll make ill informed posts?

Well he sure caught you, did'nt he.

I think you'll find, if you think about this properly, that it's not me that's been caught.

But should twice as many pixels give twice the dynamic range, simply
because you could sample two pixels for a value with twice the range
of a single pixel?

Completely the opposite. A single Bayer pixel is actually the
combined output of at least four adjacent photosites, often
more...Make the photosites smaller by increasing the "resolution" and
it just increases noise whilst allowing slightly more detail to be
captured (and I do mean slightly more) its normally at the expense of
pixel level image quality....There is no such thing as a free lunch.

Got that back to front. A single Bayer pixel is a single photosite,
receptive to one of three light wavebands.

Your totally wrong...If I were you I would learn how Bayer sensors
work before reaching for your keyboard and making embaressing
statements.

If you're totally wrong, everyone who's right looks wrong. My statement was correct in fact. If you go on disputing it, you could make a big fool of yourself.

There is no such thing as
'pixel level image quality'

Wrong again.

  • a pixel cannot record an image, it can

only record a single value (unless it's a Foveon pixel) to measure
the light incident on its own area.

Foveon sensors have much better pixel level quality than any Bayer
sensor yet made, irrespective of sensor size or pixel count.

Again, there is no such thing as pixel level image quality, because a single pixel cannot produce an image, the image can only be produced by an aggregation of pixels. You could stretch a point and talk about 'per-pixel image quality', which has a reasonably sensible interpretation (image quality, however you would measure it, divided by the number of pixels), but pixel level image quality is an absurdity. People who know more about sensors and image production than me (such as Joe Wisniewski or Iliah Borg) seem to not share your view about the qualities of the Foveon sensor. I suspect if it were so good, it would have been a commercial success. I see one of its major customers has gone bust. Your statement (and your tag) reveals that you are looking at this problem through Sigma coloured glasses ( with unfortunate metamerisms) rather than rationally.

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Bob

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