Comments interspersed below.
At 3:25 AM +0000 12/22/02, olympus-digest wrote:
>Date: Sat, 21 Dec 2002 01:30:39 -0800
>From: Moose <olymoose@xxxxxxxxxxxxx>
>Subject: Re: [OM] Re: Dipping our Toe Into Digital
>
>Whoa! Check your assumptions. The Mpix numbers advertised for DCs are
>approximately the number of 3 color pixels delivered in the output
>(after all that complicated stuff you did). My 2.1 Mp camera produces
>1600x1200 pixel images with 19,200,000 individual 3 channel pixels, so
>it's really a 1.92Mp camera.
Huh? Check decimal point. Ah: 1600x1200= 1,920,000 pixels, but each pixel is
of just one color, red, green, or blue, so we don't have the equal of a camera
with 1.93 million tri-color pixels. The ratio of colors is 1:2:1 for R:G:B, so
there are 1.92/2= 960000 green pixels, 1.92/4= 480000 blue pixels, and 480000
red pixels. The resolution is set by the green pixels; the other colors are
interpolated to fill in the missing values. So, a 2.1 Mpix camera actually has
0.96 Mpix of true tri-color resolution.
Actually, one needs always to look for the "optical resolution", as the
1600x1200 may have been interpolated from a lesser number of actual CCD pixels
(of any color). The true resolution cannot exceed the optical resolution,
regardless of the nominal resolution of the format. Interpolation cannot
supply the missing picture detail.
Scanners also suffer from this same marketing malaise.
When comparing various cameras and scanners, we probably should always
ascertain the optical resolution of the green channel alone, and use that as
our comparison. These numbers will be directly comparable to the resolutions
of black&white film and cameras.
>I think most of them quote the raw specs of
>the sensor, rather than the output of the actual camera design. It's
>sort of like the way disk drive manufacturers advertise capacities in
>decimal so that a 60mb drive is 60/1.024 or 58.59 mb to a digital
>system. In both cases, the biggest number that is even sort of
>defensible is used for promotion.
Exactly. In sum: Your mileage may vary.
>So, using your approach, but adjusted for the way Megapixels are quoted
>for DCs and adjusting for promotional inflation, you need about 9 Mp to
>equal 35mm film (even less for 25mm film!) I'm not necessarily agreeing
>with the 9 MP number here, just disagreeing with your assumptions and 26
>Mp conclusion.
Not so. My claim is that one needs more like 25 Mpix (sum of red, green, and
blue pixels in 1:1:1 ratio), which is the equivalent of 8.64, call it 9 million
tri-color pixels.
>Where it comes to where the rubber meets the road for me, all these
>calculations don't mean much, it's the images and how people
>react/interact, "see" them. It's clear to me that digital camera output
>has certain qualities that differ subjectively from film and scanned
>film. In the particular case of my eyes and those of friends and family,
>DC prints are superior to 2720 dpi scanned 35mm prints for certain
>common subjects at 8x10 and smaller. Assuming that's about the limit for
>1.9 Mp, one would need about an advertised 8.4 Mp for 16x20, which is
>about the limit for sharp 35mm prints using lenses of the quality you
>assume and reasonable technique.
While beauty is in the eye of the beholder, I would comment that there is a lot
of equipment in the chain from scene to photograph in each case, and if any
element in the chain isn't up to standard, the photos won't be good. So, I
would be cautious about making sweeping generalizations from two photos or two
specific sets of equipment.
>So your marhematical and my subjective approach end up pretty close. On
>the other hand, C.H.'s examples make it empicically clear that 4000 dpi
>(157dpmm) scans reveal more detail from at least fine grain film than
>2700 dpi (107dpmm), so your 100 pixel calculated value may be suspect?
>It leads one to suspect that something closer to the 18 Mp otheres have
>come up with may be required to reach the resolution of fine grained
>35mm film.
I used the 100 pixels per millimeter as a nice round number representative of
films and cameras in wide use, because the question was ultimately about the
behaviour of a mass market.
I would bet that anybody on this list can beat that value if they try.
That said, it may simply be that the 4000 dpi system has better optics and
focus control than the 2700 dpi system, not that either claimed resolution is
at the limits of film resolution.
Actually, this leads to a good question for CH: Has he or can he measure the
resolution of his scanners? If one can find a suitable resolution chart and
scan it, it ought to be easy. The scanner maker probably also knows, but may
not be willing to publish the modulation transfer function.
Joe Gwinn
>Moose wearing a Walt mask
>
>Joe Gwinn wrote:
>
> >Comments interspersed below.
> >
> >>>From: Albert <olympus@xxxxxxxxxxx>
> >>>
> >>>with the introduction of the Kodak 14Mpx SLR, it would seem like you
> >>>can get what you never thought possible before, Medium format quality in
> >>>a 35mm SLR.
> >>>
> >>>
> >>That depends on whose numbers you believe. My research indicates that an
> >>optimal 35mm frame may contain as much as 18Mpx. Medium format may contain
> >>40Mpx.
> >>
> >>
> >
> >Reasonable 25mm film cameras resolve something like 50 line pairs per
> >millimeter; sometimes better in the center, sometimes less at the edges. At
> >two pixels per line pair, that's 100 pixels per millimeter. A 35mm frame is
> >24 by 36 mm, so we have (24*100)(36*100)= 8.64 million pixels (each having
> >all three colors), or (8.64)(3)= 25.92= 26 million pixels (as usually quoted
> >for digital cameras).
> >
> >So, 18 Mpix is a bit low to be "optimal", but it isn't that far off: 26/18=
> >1.44 to 1.
> >
> >
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|