True resolution

Learn aboutTrue resolution

Do Megapixels Tell the Whole Story?

14 Megapixel SLR vs 14 Megapixel Digicam
Image of two 14 megapixel cameras: slr vs digicam Two 14 megapixel Sony digital cameras: A550 SLR and W320 digicam. Read on to discover the real story behind a camera's true resolution.

The answer is a resounding no, the megapixel rating on a digital camera is a poor measure of a cameras ability to resolve detail and therefore is a poor spec to compare. Unfortunately most consumers don't know this, no surprise: this is not how cameras are marketed to the public. That's why we calculate true resolution so you can understand how many megapixels a camera really has. True resolution provides an estimate of the maximum resolution a camera can resolve based on average shooting conditions and some fancy physics.

Digital Cameras with High True Resolution

These digital cameras excel against all others in their ability to resolve detail. If resolution is important to you should consider these but should also read our study: How much resolution do I really need to fully understand how much resolution is necessary.

Cyber-shot WX50 - 9.7 MP
Sony Cyber-shot DSC-WX50 The Sony WX50 is one of the highest resolution ultra compacts.
See more high resolution ultra compacts
Cybershot DSC-RX100 - 20 MP
Sony Cybershot DSC-RX100 The Sony DSC-RX100 is one of the highest resolution pro digicams.
See more high resolution pro digicams
M Typ 240 - 23.7 MP
Leica M Typ 240 The Leica M Typ 240 is one of the highest resolution mirrorless interchangeable-lenss.
See more high resolution mirrorless interchangeable-lenss
D7100 - 24 MP
Nikon D7100 The Nikon D7100 is one of the highest resolution entry-level DSLRs.
See more high resolution entry-level DSLRs
D800 - 36.2 MP
Nikon D800 The Nikon D800 is one of the highest resolution pro DSLRs.
See more high resolution pro DSLRs

The Science Behind True Resolution

Airy Disks Determine Resolution

Because of the way light works (it's actually a wave) it can only be focused to so small a point. The size of that point dictates that there is a maximum resolution that can be projected on a given surface area.

Airy Disk Example
Image of four airy disks using red gren blue and white light. Red, green, blue and white Airy Disks are captured at f/20 using 4.65μ pixels. Credit: JMZawodny via Flickr.

Sensors on cameras range drastically in size, for example a 864mm² full frame sensor has 30x the surface area of a 28.5mm² digicam sensor. That means the digicam's pixels are going to take up a lot less space on the sensor. In fact with most digicams the pixels are so small that they are essentially wasted - the smallest point that the light can be focused being many times larger than the pixels.

The smallest points are called Airy Disks, it's difficult to see them in an image because you're focusing an entire scene so it just ends up looking like blur, here's a example of Airy Disks @ f/20 with 4.65 micron square pixels used to capture them.

You can see the Airy Disks because only 4 light sources are being focused onto the sensor. The dots show the maximum physical resolution and demonstrate how the pixels are basically wasted. The size of the Airy Disks depends on the focal length - the higher the focal length the bigger the Airy Disks and at f/20 those are some big disks - the 4.65 micron pixels are just a little smaller than you'd see in a full frame sensor SLR. There is no way to make those green, red and blue dots the size of a single pixel, in fact in this example 25 pixels are being used to capture the brightest spot in the Airy Disk ( the puddle effect is the result of lights wave nature. This example is using fairly large pixels (4.56 micron), many digicams have pixels around 1.5 microns or 1/3 smaller can, that means a digicam (if it could shoot at f/20) would be using over 200 pixels to capture a single Airy Disk.


How Many Pixels per Airy Disk?

Pixels per Airy Disk
Image of pixels being used to fully cover an airy diskMathematical relationship between an airy disk and the number of pixels required.

It can be argued that a ratio of 1 pixel to Airy Disk is insufficient to capture the bleeding and gradients, which do represent some level of extra information. We feel that 4 pixels per Airy Disk is more than sufficient to capture that detail and permit some extra sharpening either by the camera or post process. The illustration indicates that the hypotenuse of each pixel will be 1/2 the diameter of the airy disk. For calculating true resolution we use an f-stop of 5.6 which is happy medium and fairly typical. The true resolution represents the maximum you can expect to achieve with the camera you're using. That being said achievable resolution will be less given imperfect lenses, jpeg compression, noise reduction routines, imperfect operators, etc.

Cameras with the Biggest Pixels

The following cameras from the last two years have the biggest pixels, that means they are the least likely to be wasting pixels.

Cyber-shot WX50 - 1.8 µm²
Sony Cyber-shot DSC-WX50 The Sony WX50 is one of the ultra compacts with the largest pixels.
See more ultra compacts with large pixels
Cybershot DSC-RX100 - 5.8 µm²
Sony Cybershot DSC-RX100 The Sony DSC-RX100 is one of the pro digicams with the largest pixels.
See more pro digicams with large pixels
M-E Typ 220 - 47.7 µm²
Leica M-E Typ 220 The Leica M-E Typ 220 is one of the mirrorless interchangeable-lenss with the largest pixels.
See more mirrorless interchangeable-lenss with large pixels
K-5 II - 23.1 µm²
Pentax K-5 II The Pentax K-5 II is one of the entry-level DSLRs with the largest pixels.
See more entry-level DSLRs with large pixels
D4 - 54.3 µm²
Nikon D4 The Nikon D4 is one of the pro DSLRs with the largest pixels.
See more pro DSLRs with large pixels

Real World Example

Image for Comparison
Sample image shot on a 5d Mark II Sample photo shot on an EOS 5d MkII

We've analyzed a 21 megapixel photo taken with a Canon 5d MkII - full frame SLR and used this to illustrate the difference between a full frame and typical digicam sensor. We calculated the true resolution of a 6.2mm x 4.6mm sensor @ f/4 and used that to illustrate how big the airy disks are relative to the true resolution. The true resolution of the full frame camera is the same as the rated megapixels, but with pixels bigger than the airy disks. Conversely, the digicam's tiny pixels are so small that it takes about 8.5 pixels to make up an airy disk - a complete waste of those little itsy bitsy pixels.

Image Crops

28.5mm² Digicam Sensor Crop
Image of digicam sensor crop 100% crop of the 14MP 6.2mm x 4.6mm digicam sensor, resized to the same size as the full frame crop.
864mm² Full Frame Sensor Crop
Image of digicam sensor crop 100% crop of the 21MP 36mm x 24mm SLR sensor.

You can immediately see the difference between the two sensors that belies the rated resolution. At an f-stop of 4 the 14MP digicam has a true resolution of 7.8MP vs 21MP for the full frame SLR (which is limited by the lens and operator at such high resolutions not the airy disks or sensor).

Digicam Airy Disks

We're showing a 2nd crop within the crop above represented by the black square. The first thing to notice is how much total sensor area is used to capture the detail - about 46 microns across, hardly any at all, the camera is trying to focus the scene on too small an area and the limitations of the airy discs are presenting themselves. You can see that a digicam sensor packed with 14 megapixels is simply capturing detail that just is not there, a suitable scaling algorithm on much larger pixels would accomplish the same.

Airy Discs with a 28.5mm² Digicam Sensor
digicam image crop showing pixel size vs airy disc size

Full Frame SLR Airy Disks

Relative to the digicam the SLR is attempting to focus this portion of the scene on 212 microns width of sensor (almost 5x the width), because of this the airy disks are much smaller relative to the sensor area. Put another way the full frame has such a large sensor that it has relatively ginormous pixels, actually larger than the airy disks - no waste. You can see that a full frame sensor packed with 21 megapixels is a very reasonable proposition. The benefit of focusing the scene on a larger area means more detail is being capture.

Airy Discs with a 864mm² Full Frame SLR Sensor
full frame image crop showing pixel size vs airy disc size

Conclusions

  • Don't blindly trust the megapixel rating on a camera - use Snapsort's true resolution rating to get an understanding of the real world capabilities
  • Read more about resolution to understand why just a few megapixels could be enough
  • Learn more about other features in a camera - there's a whole lot more to cameras than their mega pixels

Related Info

Discussion

Showing 25 comments

Avatar for Youlu Zheng Youlu Zheng (8:46 PM, June 11, 2013)
Dear Billy, You do have advantage with your native tongue (or just English name). My writing is not perfect, and my last name is even worse, but I am a proud Chinese American, and my book was published by Oxford University Press. (You can find my name with the publisher if you're smart enough, and I do not try to hide behind an alias.)

Still, I am unsure how my writing offended you.
 
Shamik (7:25 PM, June 11, 2013)
I cannot actually decide which one to buy, Nikon D3200 or D5100? Both are almost having same or equal features except that D3200 has more megapixel. Please suggest which one would provide me with better photography experience and image quality.
 
Mamey (9:29 PM, June 08, 2013)
Billy, by any chance your actual name is "Hill"-Billy? The guy wasn´t born in an English-speaking Country, but who cares? May be we could get a couple of good ideas from Zheng. Just get a life, man, and stop dating cousin Mary-Lou, otherwise the kids will have "lazy" eyes, hehe.
 
Avatar for Mike Svitek Mike Svitek (7:29 PM, January 18, 2013)
I think the "uses" was a typo. Other than that, I didn't catch any serious mistakes in his/her argument... And I read it all the way through.
Maybe you should just stop being a Grammar Nazi and begin paying attention to the valid points in the argument, not the three words that aren't in the proper formatting.


Cheers!
 
Avatar for Mike Svitek Mike Svitek (7:24 PM, January 18, 2013)
Its probably too late, but a higher number of pixels is better if you have enough light to expose them all properly. Once you need higher ISO performance and better Dynamic Range, you should start looking at dropping resolution for the benefit of an increased pixel size. I have a Pentax 645D with its huge pixels and a 40Mpix resolution but, in good light, it will be about on-par with my Nokia 808 PureView with its 38Mpix sensor...
That being said, the dynamic range I can achieve with the 645D is equivalent to the Nokia taking a perfect HDR image of about 5 photos...

You have to pick what's most important to you, then pick the camera's specifications after.
 
Avatar for Mike Svitek Mike Svitek (7:19 PM, January 18, 2013)
Lenses were rated in lines per mm (or inch) in the days of film... Those were typically rated for up to 5000 lines/mm which will out-resolve any modern DSLR sensor (You'd need to cram over 4 Gigapixels into a full-frame sensor to out-resolve that)... I don't believe modern lenses have decreased their quality since my grandpa's 70 year old Pentax glass was made, so you might as well note even mention the possibility of any sensor out-resolving a camera lens...

(Leica Summicron 35mm f/2 lens is the king of resolution, rated at 7500 lines/mm... That will resolve 6,480Mpix)
 
21 limited. (2:22 AM, November 10, 2012)
The pixel size of K-30 is about 4.8 mu, and in terms of resolution, it's hard to compare because you use different lenses on different systems. but the Pentax K-5 IIs is probably the highest resolving APS-c system and is on par with the 24 MP D600. If you blow up a K5 IIs image it will be pretty much identical with a D600, or 5DIII. But the old thing about pixel density and resolution, and even sensor size and resolution isn't holding up as far as I can tell. You can't tell anything looking at numbers, you have to test images.
 
billy (6:39 PM, September 15, 2012)
@ YL Zheng,
It is so funny that there is always, in every forum, a commenter that uses dizzying mathematics to show off their aptitude! Yet despite your amazing math ability, your writing composition stinks! I could send you a long list of questions regarding your sentence structure and vocabulary. I know for sure the first thing you will say is, "English is not my first language" but really no one cares! If you want to be taken seriously put the calculator down and learn basic grammar! Nobody is impressed with a guy who can calculate the world but can't articulate for crap! Math and science is real handy but vocabulary and communication are equally important!
 
Geos (5:35 AM, March 22, 2012)
I'm sure this is basic knowledge to most, but I'm a beginner. Does a high number or a low number represent the better true resolution? What true resolution number should I consider "good" true resolution?
 
Makjabari (1:29 PM, March 13, 2012)
what this mean, is the slr sony better than aps-c camera of nikon
for example
sony slt-a65 vs nikon dslr-d7000
 
YL Zheng (9:33 PM, March 11, 2012)


Thank you for the great article, which is a good attempt to
explain and simplify the theory about resolution.  A few questions here:


1.      
In the last figure under "Full Frame SLR
Airy Disks", you uses a 36mm x 24mm 21 MP full frame sensor for
illustration.   Assume a 1.5:1.0 aspect
ratio, the theoretical resolution is 5612x3742. 
That is close enough to my 21.3 MP Canon 5DII of 5616x3744.  So the diameter of a pixel should be 6.14
micron.  However, in this figure with 39
pixels counted per row with the width 212 micron, each pixel is only 5.44
micron as you displayed.  How does the
difference happen?


2.      
In the same figure,  you say this full frame sensor is
"almost 5 x the width" (of the 6.2mm x 4.6mm 14 MP sensor), which is
apparently far away from the right number of 36/6.2 = 5.81.  Should it be corrected as "almost 6 x
the width"?


3.      
We all know the size of Airy Disk varies and
depends on lens focal length and aperture size.    With the factor of lens imperfectness
taking into consideration, Canon and Nikon, among other brands, decide to use
pixels numbers ranging from 12.1 MP, 21.1 MP and 36.2 MP for their full frame sensor
cameras Nikon D700, Canon5DII, and Nikon D800 respectively with different
philosophy and marketing strategy.   But
the real question practical to photographers is how to use the setting to
maximize the resulting image quality.    We don't know how the sensor is used when a
photographer sets the camera resolution to less than the highest setting.   The question is, for example for the Nikon
D800, when the camera is set to, say, 4800x3200 instead of the highest 7360x4912,
how does the image quality in terms of "true resolution" compare to,
assuming a perfect lens,  


o  
The highest 7360x4912 image cropped to similar
size with longer focal length lens


o  
3000 lines/inch as the maximal available resolution
in real life measurement used by many standard tests.


o  
Nikon D700 at the maximal resolution of
4256x2832 with the 12.1 MP full frame sensor.


If the answer is "equivalent", or
at least "close enough", the Nikon D800 with 36.3 MP has the
advantage of providing more choices for the photographers, at least.


4.     For the same situation in the previous
question, what is the effect of lower resolution setting on low light
noise. 


5.     How are different ISO settings implemented
with a full frame sensor camera?


 


Thanks in Advance.
 
Thakur Dalip Singh (6:11 PM, March 08, 2012)
Great article.
 
Pete (7:46 PM, March 04, 2012)
The lack of camera going head to head is a major weakness in your 'true resolution' megapixel-myth busting exercise.  I did some testing - a small 14 megapixel sensor Sony W series against a 10 megapixel APS-C camera (with a terrific lens).  Even with plenty of Unsharp Mask the APS-C sensor could not match the tiny Sony sensor for detail - with both tested at low ISO.  Your theory has a big hole in it.  Now if you argued that small sensors have other serious failings (like poor files at 400 ISO and above) you'd have a theory that matched reality.  Go test (fairly)!
 
KKramer117 (1:50 AM, January 19, 2012)
Hi I have the Sony HX100V which is advertised as 16.2 megapixels but the true resolution on this site is 9.7 mp. If I stop the resolution down to 12, or 10 mp, will the true resolution change to 12or 10 mp? or will it go lower than 9.7 mp. You can email me at KKramer117@gmail.com or just here
 
Makjabari (2:05 PM, September 30, 2011)
i want to ask>>> like sony slt 65 its pixel size is 15.5 , while nikon d5100 is 22.5 mm2>>>
so which is better, and is it true that its sensor pixel size of new sony camera is 15.5
 
Miran (7:55 PM, September 06, 2011)
wich one have the better image quality..nikon d5100 or canon 550d?
 
Miran (7:52 PM, September 06, 2011)
wich one have the better image quality...nikon d5100 or canon 550d???
 
Avatar for Tarita Kulkani Tarita Kulkani (11:06 AM, July 27, 2011)
nice info....could you pls let me know what is camera resolution sensor?
 
AR (2:26 PM, July 08, 2011)
I'm busy hunting for a new camera at the moment.  I will primarily be using it to photograph my paintings in order to sell prints.  The site I will be selling prints through offers print sizes of up to to 40” x 60”.  My budget is £500 so obviously I will be limited by this, but I'd be grateful for any recommendations.
 
SamKay (5:09 AM, June 09, 2011)
1. What I uploaded to TinyPic were all 4608x3456. That was the 16mb size, so anything that got smaller because of the downsized settings I chose to do the experiment with got boosted back up to that size. I assume TinyPic resized them to save space.
2. The reason I added that I thought the 5mp looked "better" "to my eye" is because I'm aware of the fact that in the tradeoff between less noise and better overall "quality/detail", untrained eyes tend to prefer the muddier, less detailed/less noisy shots, while more trained eyes still prefer the more detailed/more noisy photos. That's one of the things I enjoyed about having the opportunity to post here -- essentially, to learn more about my camera and understanding what I'm doing and seeing and how changing the settings affects that, and, hopefully, learning how to get the most/best out of the combo of the camera and myself.
3. The thing that I focused heavily on (some pun intended) was the Picasso sig. It's definitely clearer/less noisy, at least at regular viewing size, in the 5mp resize. On the other hand, I think the wood paneling looks more natural/realistic in the 16mp shot. As in life...it's a series of tradeoffs.  :D
4. Thanks for taking the time to respond.
5. I'm now struggling mightily trying to decide whether to keep the FH24, step up to the ZS8, or jump on a G1 with the 14-45 kit lens (new, not used or refurbed) that's currently selling on Amazon for what seems to me to be an insane $249 + $6.99 shipping
 
Avatar for Snapsort Snapsort (1:37 AM, June 09, 2011)
Hi Sam, great job with the experiment, that is for sure the only way to figure this type of stuff out.

I'm a bit swamped at the moment, but I took at look at the photos and here are my thoughts:1.  Are these crops? They are all 1600x1200
2.  The 5mp image looks poor I think, it may have no noise but its lost any/all detail. The wood paneling looks smeared. This is often the trade off - getting rid of noise usually gets rid of detail/sharpness too.3. The 16mp w/o flash seems to have the most noise, but its really not too bad I don't think.
 
Sam Kay (7:18 AM, June 06, 2011)
NOTE: Sorry...typo...I purchased a Panasonic FH24.
 
Sam Kay (4:57 AM, June 06, 2011)
Hi. After reading your article I was also curious about what Jock was asking. I just bought a Panasonic LH24, which, unfortunately, has jumped into the 16mp hype parade. I bought it despite the 16mp, not because of the 16mp, and was wondering if I could get better results (i.e. less noise) by shooting at 5mp in iAuto mode (the only downsized option), and 10mp in "Normal" mode. I took 4 similar photos -- 2 in native 16mp mode, 1 @ 5mp in iAuto mode, and 1 @ 10mp in "Normal" mode. I then loaded them into PSP 9.0 and resized the smaller photos to match the size of the photos taken @ 16mp size. I didn't notice that much of a difference in the one taken at 10mp in "normal" mode (both the 10mp and the 16mp were taken with flash), although it seemed to have marginally less noise. But I definitely noticed a difference in the photo shot at 5mp (both of which were taken without flash), once it was resized to equal the one taken @native 16mp in iAuto mode. There was clearly less noise in the resized version, at least to my eye. This leads me to believe that I can get better, less noisy photos using the smaller sizes vs. the native size. (Note: I zoomed all of the final images to 250% in PSP to check for noise.)

This image was taken in "normal" mode @ 16mp w/flash: http://oi55.tinypic.com/20f83g5.jpg

This image was taken in "normal" mode @ 10mp w/flash & resized (it's a little brighter, I'm not sure why. But it has nothing to do with the resizing): http://oi52.tinypic.com/156y1iu.jpg

This images was taken in iAuto mode @ 16mp w/o flash: http://oi53.tinypic.com/6z54dy.jpg

This image was taken in iAuto mode @ 5mp w/o flash & resized: http://oi54.tinypic.com/15xan90.jpg

(Please don't judge the composition of the photos. I was just shooting what was at hand to test the theory about which photos would have less noise.)
 
Avatar for Snapsort Snapsort (4:10 PM, May 20, 2011)
Why don't you give us a better idea what you will be doing with the camera, and then we can try to point you in the right direction. I would not get hung up on resolution, unless you are printing our a billboard size images, most people don't need more than a few megapixels.
 
Von Alois (3:57 PM, May 20, 2011)
 what is the best digicamera in true resolution ? and a low price one .