I am trying to find out the definition of a megapixel? Some references on the web place it at 1 million pixels, and other places say it is equal to 2^20 = 1,048,576 pixels.
About a million.
I think that in general due to rounding — and more importantly, other real world factors which mean that megapixels only relate loosely to actual resolving power — it doesn't really matter if "megapixels" is binary or decimal. It is a useful term because it happens to be in the range where we get human-useful small numbers with the digital cameras (so far). It's rarely used to mean a precise value — one 16-megapixel camera will likely generate photos with a slightly different size than one from another brand.
For the same basic reason, "kilopixel" isn't a real word, because there's no particular case where it would be useful.
Overall, a lot of us coming to photography from a tech background, be it programmer, engineer, or otherwise, have a tendency to look for precision. When it comes to exposure, anything under a third of a stop is unlikely to be a big deal, and when it comes to pixels, a similar basic rule makes sense: until we're talking about doubling or halving the number, don't sweat it.
I originally posted this as a comment to another question, but I think it answers this one.
To answer you have to understand what a
In digital imaging, a pixel, or pel (picture element) is a physical point in a raster image, or the smallest addressable element in a display device.
Mega being a unit prefix, it simply means
1'000'000. Knowing that, 12 Megapixels means simply 12'000'000.
This said, when your camera constructor displays 'Around 14.3 Megapixels' in the data sheet, it's a simplification to avoid writting stuff like : 14,204,928
This value being calculated from the resolution of the pictures you're taking : 4352 x 3264
pixels = 14,204,928
It depends how you count but almost every company multiplies the number of photosites and divide by one million. They rarely make the distinction if those photosites are next to each other or layered. For this reason, a 45 MP Sigma SD1 makes an image which has the same resolution as a 15 MP Canon 50D.
They sometimes quote two numbers, effective megapixels and actual. Effective are the ones that make into final maximum resolution images and which may be a little less than the actual ones which are how many are on the sensor. Some of these may be masked out to read the back levels and others lost because of the imaging area of the lens.
In computing, when talking about kilobytes, and megabytes, the terms kilo and mega have traditionally been modified, letting kilo=2^10, and mega=2^20.
This has led to confusion, because hard disk manufacturers would use megabyte to indicate 1 million bytes instead of 2^20 (resulting in more impressive numbers).
But when talking about something different than bytes, kilo and mega should still refer to their original meanings, one thousand, and one million.
Thus a megapixel should be 1 million pixels. But this can often be an approximation. E.g. my 18 megapixel Canon EOS 7D 'only' has 17.9 million pixels.
It depends on whether you're selling or buying. When you're writing marketing literature, you want the Mpix number to be as high as possible. That means you use 106 for "mega". When it's to your advantage to make the number look small, you use 220, which is 1,048,576.
In reality, a 5% difference in the total number of pixels is pretty much irrelevant. Note that the linear resolution goes with the square root of the total number of pixels, so 5% more pixels is only 2.5% more linearl resolution. You won't be able to notice that difference even in two prints at the proper size you get to compare side by side.
I would like to also say that each "pixel" in a DSLR is actually only a portion of a pixel. So, the sensor itself has say, sensitive light elements for an R and a G and a B, and maybe another G. Now, these three, or four, together should form a single pixel but it don't. They interpolate it and make the four, count as four pixels.
Or something similar (http://en.wikipedia.org/wiki/Bayer_filter)
This means that your 20 megapixel camera might actually be a real 5 megapixel camera but it's interpolated up using algorithmic magic.
Same applies to the LCD screen. A "1 million dot" screen only has 300kish pixels. Sadly.
I can give you the easist way to findout what is Mega Pixel and how many pixels is 1 Mega Pixel. It is calculated by tha same way how the Memory unit is calculated.. 1000 Bytes are 1 KiloByte 1000 KiloBytes are 1 MegaByte (1 Million Bites)
So we can simply calculate it by this way 1000 Pixels are 1 KiloPixel (The word KiloPixel is not officially used, I've used that word to define about pixels to you) Then 1000 KiloPixels is 1 MegaPixel (1million Pixels).....
A Camera With 96x128 Pixels is a 0.012MP Camera (or 12KP Camera) A Camera With 120x160 Pixels is a 0.019MP Camera (19KP) A Camera With 240x320 Pixels is a 0.07MP Camera (70KP) A Camera With 320x480 Pixels is a 0.15MP Camera (150KP) A Camera With 360x640 Pixels is a 0.23MP Camera A Camera with 480x640 Pixels is a 0.30MP Camera A Camera With 480x854 Pixels is a 0.40MP Camera A Camera With 540x960 Pixels is a 0.51MP Camera A Camera with 600x1024 Pixels is a 0.61MP Camera A Camera With 768x1024 Pixels is a 0.78MP Camera A Camera With 720x1280 Pixels is a 0.92MP Camera (920KP) A Camera With 960x1280 Pixels is a 1.22MP Camera A Camera With 900x1600 Pixels is a 1.44MP Camera A Camera With 1200x1600 Pixels is a 1.92MP Camera A Camera With 1080x1920 Pixels is a 2.07MP Camera A Camera With 1440x1920 Pixels is a 2.76MP Camera A Camera With 1536x2048 Pixels is a 3.14MP Camera A Camera With 1440x2560 Pixels is a 3.68MP Camera A Camera With 1800x2400 Pixels is a 4.32MP Camera A Camera With 1920x2560 Pixels is a 4.91MP Camera A Camera With 1944x2592 Pixels is a 5.03MP Camera A Camera With 2048x3072 Pixels is a 6.29MP Camera A Camera With 2448x3264 Pixels is a 7.99MP Camera A Camera With 2160x3840 Pixels is an 8.29MP Camera A Camera With 3072x4096 Pixels is a 12.58MP Camera A Camera With 2880x5120 Pixels is a 14.74MP Camera A Camera With 3264x4896 Pixels is a 15.98MP Camera A Camera With 3600x6400 Pixels is a 23.04MP Camera A Camera With 4096x6144 Pixels is a 25.16MP Camera A Camera With 4320x7680 Pixels is a 33.17 MP Camera A Camera With 5720x10240 Pixels is a 58.57MP Camera
It is easy to calculate... When multipliying any of the given resolutions above, you will get the same answer with 100% accuracy...