

The megapixel myth - henning
http://www.kenrockwell.com/tech/mpmyth.htm

======
gaius
I used to work for... A press agency you've all heard of. We had lots of big
prints up about the place. Now, some of these were shot on films like Fuji NPZ
(ISO 800 colour negative) or first-generation photojournalist DSLRs (e.g.
Nikon D1H, 2.1MP). At 60x40", they looked _great_. Nikon knew this; their
second generation was "only" 4MP (D2H).

What matters in resolution is lp/mm; that is how many distinct pairs of black
and white lines can fit within 1mm. See here:
[http://www.bobatkins.com/photography/digital/size_matters.ht...](http://www.bobatkins.com/photography/digital/size_matters.html)
The long and the short of it is, unless you are shooting on a tripod with a
cable release and a prime lens, there's really not much point worrying about
megapixels. I once had a huge row with people on a mailing list about this;
try as I might I couldn't make them understand the simple idea that it doesn't
matter how many pixels you have if they can't all be assigned distinct values,
there's no additional resolution there. They were the kind of people that
bought the most expensive DSLR and stuck the cheapest lens on it. Then again
if you'd spent 5 grand on a camera and someone did the maths for you you might
be upset too... ;-)

Also note that cinema is only 2000 pixels across.

~~~
pedrocr
lp/mm is just a unit of measure for resolution and is directly constrained by
the number of pixels. You can't resolve 10 lines with less than 20 pixels and
in practice you need more.

The article you quoted compares the same resolution in different sized sensors
to show that smaller sensors need to resolve more lp/mm in sensor area to
achieve the same file in the end. It shows that for the same MP count a larger
sensor is better. What we are discussing is the opposite, for the same sensor
size MP count is better. And as far as resolution is concerned that tends to
be the case, even if the lens is the biggest bottleneck.

In DSLRs we're getting to a point where resolution is more constrained by
camera movement and lens quality than number of pixels but at the same time
both those bottlenecks are being addressed with modern lens design and anti-
shake techniques. We've come a long way in actual practical resolution from
the 2MP/4MP cameras you mentioned.

~~~
acqq
> for the same sensor size MP count is better

That's very wrong. The number of photons is limited, the effective light-
sensitive area drops with more MP, and with small sensors with more MP you
then get more noise than a signal. It's hidden by post-processing but that
also drops the real information. So less MP is better in a lot of common
circumstances.

~~~
pedrocr
If you keep reading:

>And as far as resolution is concerned that tends to be the case

I was only talking about resolution. Lower MP gives you less noise but it
won't give you more resolution. In the extreme case where you push the ISO
maybe the extra noise can overcome the extra resolution. To make it simple
lets say that at base ISO on a sunny day the higher MP will out-resolve the
lower MP for a given sensor generation.

My point isn't that low MP isn't good for many applications it's that saying
that higher MP doesn't lead to higher resolution is just wrong. If you want
resolution you need pixels to produce it and current cameras are mostly not
wasting the resolution away.

The excessive MP problem only really exists in consumer compacts. High-end
compacts and DSLRs haven't been stretching the limits too much. The highest MP
DSLRs right now have 24MP on a full-frame sensor, which is about the same
density as 10MP on an APS sensor. Some of the APS ones have pushed that on to
~16MP with accompanying improvements in the individual pixels. Maybe you're
thinking of camera phones with 8MP, those may very well be in the extreme case
you mention where noise overcomes the extra resolution.

~~~
acqq
If you exclude professionals, nobody buys "full-frame" sensors. Excluding
professionals, people don't even know what that means. Nobody brags about
sensor size, everybody brags he has "more MP" than before.

Also almost nobody wants to make photos only in the direct sunlight. Normal
conditions are conditions with less than optimal light.

So excluding "full-frame," more MP is actually worse, and people buy simply by
believing "bigger number better."

Edit: Let me stress once again: I'm not discussing a scenario of a
"professional with a slave to carry all his equipment and another guy to set
and hold the lights" but a "normal person" carrying not-too-expensive camera
or even his phone and expecting "more MP better pictures."

~~~
pedrocr
I was only mentioning full-frame as those are the highest MP DSLRs available.
I then mentioned APS cameras, which a lot of people do buy, especially the
entry level stuff. In that segment and even in less than perfect light the
higher MP cameras have been getting better, not worse.

There's an argument to be made that if the manufacturers had stopped at say
12MP (to pick a number) and put all their effort into noise we would have
better cameras now for the kind of use people actually put them through. In
fact Nikon did just that at the high-end with the D700 and D3. There isn't
however much of an argument to be made that the 16MP APS cameras of today are
worse than the 12MP cameras of a couple years back. The latest models seem to
have both more pixels and lower noise.

Maybe you'd like a lower MP camera with even lower noise and maybe you can't
buy it because MP sells cameras and thus shapes development. That could be a
problem, but saying "excluding full-frame, more MP is actually worse" isn't
really true. My impression is the complaints about MP are mostly right in
compacts and everywhere else tend to be geek snobbery.

------
stan_rogers
While he's got the ratios right, he's got a tolerance for bad printing that I
don't share. VGA for 4 x 6? Maybe if you thought your 110 Instamatic made good
enlargements (in those days, 4 x 6 was a premium print). That's newspaper
resolution. Double up the dimensions (1.2 MP) and 4 x 6 is just acceptable to
my eyes (and it didn't used to be when printer dithering algos weren't what
they are today).

~~~
michaelhalligan
Agreed, with a 12 megapixel camera I never felt printing anything over 16 x 20
was acceptable, even with my 22 megapixel 5dmk2 I don't go much larger than 20
x 30.

~~~
jonah
It all depends on how closely you're viewing them. We have a bunch of photos
shot with a 5D (12MP) printed about four feet tall. They look great from a
normal viewing distance. Of course, when you put your face six inches away,
you can start to see some digital artifacts (stair stepping, etc.) but that's
not a problem.

The maximum necessary resolution is related to the intended viewing distance.

"The standard definition of normal visual acuity (20/20 vision) is the ability
to resolve a spatial pattern separated by a visual angle of one minute of
arc." From that the maximum resolvable dot size can be calculated for a given
viewing distance.

[http://www.ndt-
ed.org/EducationResources/CommunityCollege/Pe...](http://www.ndt-
ed.org/EducationResources/CommunityCollege/PenetrantTest/Introduction/visualacuity.htm)

<http://www.clarkvision.com/imagedetail/eye-resolution.html>

(Sidenote: billboards usually printed at around 20-30ppi)

~~~
stan_rogers
20/20 is actually pretty bad eyesight. It's "normal vision", not perfect
vision, and when my eyes are "corrected" to 20/20, they're about a quarter-
diopter shy of maximal acuity. There is a huge difference to my eyes between
pictures printed at a 200-line screen and one printed at a 150-line screen
(all other things, like stock and varnish being equal) at a distance of more
than one metre (from head-height on a couch to the magazine at the far end of
a coffee table). If I were printing from a 12MP original at about four feet
tall, I'd certainly run the source through something like Genuine Fractals
Print Pro (even a good giclee pattern can't make up for squared-off curves).
At four feet in the long dimension (giving a realistic viewing distance of
about six feet) I'd notice raggedness at a glance at less than about 80ppi --
but then the dye clouds from a 4x5 negative printed at that size would drive
me batty as well.

------
lutorm
Not to mention that most of those tiny cameras with huge pixel counts don't
have optics good enough to resolve those pixels, so they _really_ are
pointless.

------
celoyd
The article’s heart is in the right place, but it overstates the case. For
example, “Sharpness has very little to do with image quality, and resolution
has little to do with sharpness” goes too far if you have a pretty good lens
and you’re pretty good at avoiding camera shake.

Pixel count is not nearly as important as marketing makes it out to be, but it
is important.

------
seanlinmt
If I'm not mistaken, the Mars Rover had a 1 megapixel camera. :)

~~~
jonah
Not only that, but it's a monochrome sensor with a filter wheel. It takes the
same shot with multiple filters and the resulting images are merged back on
earth.

My friend worked on that project.

[Edit]

It has 12μm x 12μm pixels whereas the 5D has 8μm and the 5DmkII has 6μm
pixels. However each pixel on the Canons contain three (RGB) photosites to the
rover's one.

<http://www.mwoa.org/Ch31.pdf>

~~~
Tamerlin
No, the Canon sensors also have only one photosite per pixel -- they're still
using a Bayer filter on a monochromatic sensor.

~~~
jonah
Ok, here we're getting into confusion about terminology here.

To clarify:

In the Bayer filtered Canon CCD each individual photosensor is covered in a
colored filter [1] in a pattern such as:

B G G R

So when capturing an image 1/4 of the sensors are capturing blue light, 1/4
capturing red, and 2/4 capturing green.

In contrast the CCD in the rover's cameras do not have filters in front of
individual photosensors. Instead, there is a set of filters on a disc which
are mechanically positioned in front of the sensor. Using this method three
images are taken. On each with a red, green, and blue filter covering 4/4 of
those same sensor elements giving you 2x-4x the number of elements capturing
each color and thus much higher image quality at a given resolution.

B B B B then G G G G then R R R R

Similar multi-shot technology was used in the early days of terrestrial
digital photography to provide better color, exposure latitude and resolution.
[2] for a bit of discussion on multishot vs. single shot medium format digital
camera backs.

[1] <http://en.wikipedia.org/wiki/Bayer_filter>

[2] [http://www.luminous-
landscape.com/reviews/cameras/h3d50ii.sh...](http://www.luminous-
landscape.com/reviews/cameras/h3d50ii.shtml)

~~~
Tamerlin
The part that threw me off was where you said that the Canon sensor contains 3
photosites per pixel -- which based on this pots leads me to believe that you
meant that it uses 3 photo sites to record each pixel, which is still not
entirely accurate; the Rover's capture every color at every photosite, so they
use all of their sensor's resolution. Canon (and everyone else but Foveon, for
that matter) making a single-shot sensor can't do that, they instead sacrifice
the real resolution of the sensor due to the Bayer filter, and use
interpolation to make up the difference.

------
yatsyk
What annoys me a lot is increase in megapixels in camera phones and stagnation
in tesktop\notebook screen resolution. I don't need multimegapixel camera in
phone. To share photo with friends on facebook or twitter 0.3MP is more then
enough but processing of multimegapixel image is not easy task for small ARM
processor, so you get very slow response at all phone photo capturing and
processing applications and getting annoying delays.

According to desktop screen resolution you are lucky if you can get screen
with more then 2MP resolution. And this situation is same for years. It even
getting worse after switching to wide screen because now you are getting less
pixels on same diagonal and resolution.

~~~
Yaggo
You cannot directly compare digital camera megapixels with display megapixels.
The former uses Bayer-interpolation (except very few cameras with Foveon
sensor) while the latter has true RGB pixels. In the other words, the digital
camera's pixel count of two million is shared between R, G, G, B pixels (500k
of each – yes, most sensors have double green pixels). A Full HD monitor has 3
* 1920 * 1080 (sub)pixels.

Because of Bayer interpolation, the true resolution of 3MP sensor roughly
equals 2MP screen resolution.

(Yes; I fully agree with your point that a phone doesn't need megazillion
pixels. Sensor size is more important factor when speaking of image quality.
[Not to mention the optics.])

~~~
yatsyk
I'm not comparing them directly I'm comparing increase in resolution for
camera phones and monitors. Resolution for mainstream camera phone changed
from 0.3MP to 5 MP (same Bayer-interpolated megapixels, technology is the
same) but I still need to use same 2MP (true megapixels) monitor for years.

------
bogdan_moldovan
Olympus has a great page for consumers to understand pixel-print size
relationship: <http://www.olympus.co.uk/consumer/208_741.htm>

For example, my D300s (12M) at 4288x2848 pixels can be printed at 300dpi
(professional photo prints) at a maximum size of 14.3x9.5(inch) =
36.32x24.13(cm) = a little bit smaller than an A3.

The same picture can be printed @150 dpi on an A1 (84.10 cm x 59.40 cm)
leaving a little bit of border.

------
cletus
The article referenced this:

[http://www.nytimes.com/2007/02/08/technology/08pogue.html?_r...](http://www.nytimes.com/2007/02/08/technology/08pogue.html?_r=2&oref=slogin)

The one company that seems to have a clue about this is actually Apple. The
iPhone 4 has a 5mp camera in it. Some pundits say things like "I wish it had 8
megapixels or more". In doing so, they show their complete ignorance.

Most people couldn't tell the difference between 5 and 8 megapixels. What 8
megapixels buys you is larger files, more noise and slower processing (on a
sensor this small). The size of the pixels matter. It's one reason DSLR images
tend to be so much better: they have hugely bigger pixels.

I'd love to see more good 5-8mp point and shoot cams rather than these
ridiculous 14+ mp noise factories.

~~~
ugh
Canon, Nikon and Panasonic reduced the number of pixels or kept them the same
in their high end small sensor compacts. (Canon G11: 10 MP down from 14.7 MP
in the predecessor; Canon S90 and S95: 10 MP; Nikon P7000: 10 MP down from
13.5 in the predecessor; Panasonic LX5: the same 10 MP as the 2006 model and a
slightly bigger sensor.)

The newest iPhone has a tiny 1/3.2" sensor, those high end compacts usually
have 1/1.7" sensors, that’s quite a bit more than double the area. Their
pixels are consequently a bit bigger. If Apple made the right decision Canon,
Nikon and Panasonic must have, too.

They get it and they know that at least their best informed customers (those
who actually buy high end small sensor compacts) will also get it. They are
probably only (unnecessarily) afraid of the general public, all those who buy
the cheapo point and shoots. If you are willing to pay you get appropriate
pixel densities.

~~~
sukuriant
You might want to reverse that order: "If Apple made the right decision Canon,
Nikon and Panasonic must have, too."

Canon and Nikon are optics companies. If ~they~ made the right decision, then
Apple has weight in their position, too. I don't know enough about Panasonic
to state an opinion (I'm neither saying they're bad, nor am I saying their
good. I simply know little about them)

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aaronsw
Are Ken Rockwell and Lew Rockwell related? They seem to share a web designer.

