[Leica] OT: Help! How many Megapixels needed?

[hlritter at bex.net (Howard Ritter)]

Larry, to begin with what you said last, the requirements for a good 
1-to-2-foot print and for the best 1-foot consumer magazine photos are 
rather different. The commonly accepted dots-per-inch criterion for a 
critically examined print is 200?300, meaning a minimum of about 2000 x 3000 
dots for an 11 x 14, or 3000 x 4000 for a 16 x 20. So for this you need 6-12 
MPx, or twice that for 300 dpi in the print (not a difference that?s going 
to be noticed by many viewers!). The halftone process in the best magazines 
on coated paper I believe is around 180 dpi, so the MPx needs for an 8.5 x 
11-inch magazine page would appear to be around 3 MPx. 

My 27? 5K iMac screen has about 15 MPx, with a pixel pitch of just over 
200/inch, and it produces an absolutely stunning rendering of digital images 
taken with, for example, my M240. It?s about like a 16 x 24 print done at 
200 dpi.

So to answer your question, for casual viewing of prints in the size range 
you mention, 10-12 MPx should suffice, and no more than half that for a 
large-format, high-quality art magazine page.

That said, I?d like to mention that, just out of curiosity, and wondering 
how large a 200-dpi print could be produced from a full-frame digital 
sensor, I experimented with a variety of cameras, including some 
point-and-shoot ones with small sensors and tiny photosites. All the 
cameras, fixed or zoom lenses, were used at the same actual FL, so the image 
was at the same scale on all of the sensors (different fields of view of 
course). In this respect, my 12-MPx P&S camera?s sensor was the equivalent 
of a small section (~1/30 the area) of a FF 35mm sensor with ~350 MPx. With 
that camera, I took photos at its full FL of about 23 mm and compared them 
to the M240 with a 24mm lens mounted. I also used a couple of other cameras 
with intermediate-sized sensors and appropriately selected FLs. I blew up 
the images in Photoshop and did a visual comparison of resolution. I found 
that, today's even inexpensive lenses on-axis have resolution that exceeds 
the sensor resolution until well past the equivalent of ~50 MPx in a FF 
sensor. I suspect that, for people who are going to make massive 
enlargements, a 50 Summicron ASPH would need a sensor approaching 100 MPx to 
make use of its full capabilities.

Fooling around years ago with my M8, I also found that using Photoshop to 
up-sample an image to double the pixels per inch produced an image that, 
when viewed very large, was far more pleasing than the native image and did 
quite an impressive job of mimicking a higher native resolution, though of 
course no increase in information results from this maneuver. I think this 
is because real-world images are not made of random, independent, tiny 
(smaller than sensor or lens resolution) pixels, which would not look better 
when up-sampled; rather, natural objects tend to have a large-scale 
correlation that extends across many pixels (think of the edge of a tree 
branch or a person?s arm), making up-sampling a valid way of simulating a 
higher than native resolution.

?howard


> On Oct 28, 2015, at 12:51 PM, Larry Zeitlin via LUG <lug at 
> leica-users.org> wrote:
> 
>       Here is a question discussed at a recent photo show. I had no good 
> answer.
>       
>       When I first got involved in digital photography almost two decades 
> ago I was advised by engineers at the Kodak research lab that all of the 
> information on a 35mm Kodachrome slide could be contained in 13.5 
> megapixels. They felt that it would take almost a century to reach that 
> point. (Most of those engineers are now looking for other jobs.) Remember 
> that the first antediluvian digital cameras had only .3 megapixels of 
> resolution. Film, they said, would be safe for many years. That 13.5 
> megapixel estimate seemed to take on a life of its own. The 4/3s format as 
> finally released was 14 megapixels (now 16 Mp.) and the Leica M8 and first 
> DSLRs were content with less. My first digital Leica had a 1.3 megapixel 
> sensor. I have owned cameras with 3,5 Mp, 5 Mp, 10 and 12 Mp, and 16 Mp. 
> All produced very good results to the naked eye. Admittedly I didn?t use a 
> magnifying glass to explore the details of the image. But then who does?
>       Now cameras are marketed with 24, 32, and 64 megapixel sensors. Even 
> the iPhone has 8 megapixels. Does it make any difference or is it simply a 
> marketing tool. Theoretically visual quality should improve as the square 
> root of the megapixel count but the electrical complexity of the 
> computation and the display requirements are directly proportional to the 
> pixel count of the sensor. Even Apple, a company that never backed away 
> from complex systems, needs only 5.5 megapixels to drive a 27? Thunderbolt 
> display. I view most of the LUG output on a 13? Mac Pro laptop screen and 
> the work appears perfectly adequate.
>       For people that want to produce 11? x 14? to 16? x 20? prints or 
> publish their work in most consumer magazines, not display gigantic 
> Colorama sized prints from minuscule portions of the frame area, does the 
> number of pixels really matter? Inquiring minds want to know.
>       Larry Z
> 
> 
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