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Megapixels – Are they important?

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Old 30-06-07, 15:45
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Default Megapixels – Are they important?

Popular opinion states that the more megapixels a cameras sensor has then the clearer the resulting image and therefore better quality. Camera manufacturers have for some time been involved in a race to create affordable high resolution image sensors within the bounds of AP-S and 35mm format. This article is concerned only with cameras from manufacturer Nikon and assesses resolution from three models D2Hs, D70 and D2X which have native resolution of 4.1, 6 and 12.4 megapixel sensors. Whilst the author does not hold an exhaustive range of lens charts, images are examined using the same test piece for a real life comparison. All images are assessed on equal terms but due to logistical issues concerned with supplying every reader of this article with a printed 6 x 4 photograph images are presented at monitor resolution - 72 dpi (Dots Per Inch) therefore every reader can view a representation of each photograph suitable to computer monitors.

A megapixel is a one Million picture elements so the understanding that more equates to better images is a logical one. However the truth is often realised when a photographer purchases a new higher pixel count camera and discovers that the images are often worse then their older lesser pixel count camera. When the same AF-S area of approx 24 x 16mm is used the only physical way to arrange more pixels is to employ smaller and smaller photo-sites. This may result in increased noise (unwanted speckles due to non-linear output of each pixel when subject to equal light energy) as a smaller element is not exposed to the same amount of light energy or photons as a larger one therefore electronic amplification is required to increase a pixels output level which is governed by aperture, exposure time and ISO speed. In theory all cameras regardless of manufacturer should output the same brightness for a given ISO, exposure and lens aperture. If noise prone electronic amplification is not used then another way of keeping within these bounds is to reduce the ISO speed rating i.e if the sensor output is low due to an increased pixel count then the output could be rated at different ISO level i.e. 1/125 at f4 produced half the level it should at ISO200 then a manufacturer could claim the sensor output is at ISO100 whereby the photographer can increase ISO speed to increase output. A higher pixel count sensor as well as recording more detail will record more flaws such as lens aberrations and poor technique from the human photographer. If a chromatic aberration exists from a consumer lens used on a 4MPx (MegaPixel) camera then the extent of colour shift maybe across ½ pixel and not recorded but the same lens used on a 12MPx camera could have colour shift across three pixels each side of a high contrast edge resulting in six pixels being exposed to lens aberration which could definitely be recorded. The same applies for poor technique an edge may be blurred across one pixel on a 4Mpx but this may be three with a 12Mpx image to show perfect results viewed on computer monitors at full pixel count from higher resolution sensors perfect technique must be employed.


Camera sensor specifications

D2Hs, 4.1 Million Pixels (2464 x 1632) 23.3 x 15.5mm. JFET LBCAST
D70, 6.01 Million Pixels (3008 x 2000) 23.7 x 15.6mm. CCD
D2X, 12.4 Million Pixels (4288 x 2848) 23.7 x 15.7mm. CMOS

Notice differences in physical size between all cameras and difference in sensor technology as the motivation of this article is image quality between pixel count this will be ignored and has little relevance when images are printed.

Full specifications can be found below
D2H (as only a preview D2Hs) can be found
http://www.dpreview.com/reviews/nikond2h/

D70
http://www.dpreview.com/reviews/nikond70/

D2X
http://www.dpreview.com/reviews/NikonD2X/


The Test
Testing each camera is not about any specific camera, its features or quality instead the test is concerned only with megapixel output so differences in colour, exposure and noise are ALL ignored. It must be reiterated that this test is purely concerned with megapixels.

A teddy bear was selected for fine detail in its synthetic fur and especially a course weave ribbon around its neck. All images recorded using the same 50mm f1.8 lens at f8, reviewed by Bjørn Rørslett ( http://www.naturfotograf.com/index2.html ) 'having no noticeable difference between f4 and f8'. Aperture f8 was chosen at the end of this range to provide maximum depth. A solid slik professional tripod was used to avoid any motion shake and all recorded using Nikon Camera Control Pro (computer tethered) to avoid any human induced vibration.
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Old 30-06-07, 15:49
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Fine Detail
An single area of course weave ribbon was chosen as the focus area The examined area is a 500 x 500 pixel crop and because of the difference in pixel count this area will show a larger or smaller patch of the photographic subject.



4.1Mpx file detail crop
Minimal detail is shown at native resolution but is this acceptable?
http://www.foxaviationphotography.co...mg0014crop.jpg


6.01 Mpx fine detail crop
More detail in the weave than 4.1Mpx sensor is this acceptable?
http://www.foxaviationphotography.co...mg0018crop.jpg

12.4 Mpx fine detail crop
Lots of detail in the fine weave much more than 4.1 and 6.01 Mpx sensors and quite a surprise.

http://www.foxaviationphotography.co...mg0016crop.jpg


All three images are acceptable but the level of detail provided by the 12.4Mpx sensor surpasses any expectation based on the former two. Although when looking at the fur in each example there seems to be little difference. Therefore lower resolution sensors are perfectly acceptable with certain scenes and a higher pixel count sometimes does not provide better sharper images within that scene.
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Old 30-06-07, 15:52
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Printed representations

All three images have been resized using Nikon Capture NX and their colour profile converted to sRGB for Internet viewing. Monitor resolution of 72dpi would require an image of 432 x 288 to represent a 6 x 4 photograph which is very small and would provide little value. Printed representations are instead 800 pixels high to cover most readers monitor and would equate to a photograph being nearly 11 inches along the vertical side.

http://www.foxaviationphotography.co...mg0014full.jpg

__________

http://www.foxaviationphotography.co...mg0018full.jpg
__________

http://www.foxaviationphotography.co...mg0016full.jpg

Is it possible to judge which is which? - NO!

Therefore anyone wishing to share photographs using the Internet can do so using the most modest of photographic equipment without being bogged down by the complications of megapixels. Printed photographs to approx 6 x 4 at 300dpi can be produced without any real difference.
Extra megapixels are required when printing large images but some claim the advances in bi-cubic resizing permits photographers to produce high quality enlargements from 4Mpx sensors although as seen in the native 500 x 500 crop examples that more megapixels does provide more detail if used without resizing. Extra megapixels are require more memory card and hard disk space, if using a camera to its optimum RAW should be used necessitating a very powerful computer to process and hold in memory a highly complex and large RAW image. In the examples RAW image size were in a range of 3.5 to 10.3MB hence a linear relationship between megapixel count and storage requirement although based on experience a non-linear relationship exists between computer performance and RAW image size, requiring more than three times the power to process a 10.3MB RAW file when compared to 3.5MB output from a 4.1Mpx camera in the same period of time.

So, are megapixels important?
In summary, NO! Megapixels do offer greater scope to select an area of a photograph to crop and provide greater fine detail but often negated when printing standard size photographs and sharing using the Internet. More megapixels require more hard disk capacity to hold for long term storage. Greater processing power is also required if shooting RAW mode and often have greater amount of noise. Lower megapixel sensors gather more light resulting in cleaner images but with less detail but require less storage capacity.
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Old 30-06-07, 15:59
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Quote:
Originally Posted by Stephen Fox View Post
Therefore lower resolution sensors are perfectly acceptable with certain scenes and a higher pixel count sometimes does not provide better sharper images within that scene.
Stephen,

I think you've answered your own question here. If you're doing selective crops of images that you then print at A3, then yes, pixels count. If you're taking pictures for viewing on a screen, or printing 6*4, then you can get away with just about anything, and the higher pixel count will be meaningless.

Besides, there's some photographers with some very high MPixel count cameras that still take some bad photos. Likewise, you seem to do ok (tongue planted firmly in cheek here) with your D2. Those who look at the pixels miss the big picture.

Duncan
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Old 30-06-07, 16:19
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How many times has another photographer walked up to you and asked... "So, How many Megapixels is that then?"

It happens to me almost every time I go to an airshow!
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Old 30-06-07, 17:13
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Perfect set of articles, Stephen, that should slam the lid on the megapixel argument. I'd advise anyone else still in doubt to look at some of Mose Peterson's wildlife photos that he took with an early Nikon - 2.8Mp - they are just outstanding. It's the photographer's knowledge of the subject, light, and composition that makes the image, not the number of pixels.
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Old 30-06-07, 21:37
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Quote:
Originally Posted by Stephen Fox View Post
[So, are megapixels important?
In summary, NO! Megapixels do offer greater scope to select an area of a photograph to crop and provide greater fine detail but often negated when printing standard size photographs and sharing using the Internet. More megapixels require more hard disk capacity to hold for long term storage. Greater processing power is also required if shooting RAW mode and often have greater amount of noise. Lower megapixel sensors gather more light resulting in cleaner images but with less detail but require less storage capacity.
For internet I have experience with the D2X. Images with a high level of detail I have had to shrink so much they just look nothing like the origional. Some are then not worth posting even with WPF's generous file size allowance.

Processing power - I had to get a pc upgrade before I could handle my RAW files and have just invested in a large capacity stand alone drive to hold the tiffs.

Can I see the difference on screen between a D2X and a D100 image ........ well yes I can, but then a lot of my pics are for a better word ' hard ' subjects with a lot of detail. Soft subjects like flowers, then they follow Stephens examples above and you would be harder pressed to tell the difference between D100 and D2X on resized to 1024 x 760 images. As for 800 x 600 then even in a detailed image so much is lost in the shrink that a 6mp could look better than a 12mp.

The one other thing that will make a significant difference is lens quality. Top lens on a 4mp will probably give a better resulting image than mediocre lens on 6 - 8mp camera. Foxy probably does not have access to such to prove me wrong.

Don
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Old 30-06-07, 21:49
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Quote:
Originally Posted by Don Hoey View Post
The one other thing that will make a significant difference is lens quality. Top lens on a 4mp will probably give a better resulting image than mediocre lens on 6 - 8mp camera. Foxy probably does not have access to such to prove me wrong.
Don

50mm f1.8 was the lens of choice as resolution is high and could easily provide good results on both 4 and 12 Mpx cameras.

It seems there are applications for both low and high pixel count sensor cameras.
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Old 30-06-07, 21:52
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At what point does digital noise raise its head? For small sensors as found in compacts a lot of megapixels seems counter productive as the noise suppression algorithms needed seem to make the photos worse rather than better. The 6mp compact I use a lot of the time seems about the right compromise at the moment. SLRs with their bigger sensors will have a higher ceiling.
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Old 30-06-07, 22:16
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Excellent article, a question I have wanted to ask ....
Something I note is that when stored in the camera,
a 9500Mp picture takes up 2.2 Mb. If I rotate the photo
it become 1.3mb; and if I alter the contrast, or something,
and save again, it becomes 800Kb. What is being lost,
if anything?
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