Image resolution

The resolution of a digital camera is often limited by the camera sensor (typically a CCD or CMOS sensor chip) that turns light into discrete signals, replacing the job of film in traditional photography. The sensor is made up of millions of "buckets" that essentially count the number of photons that strike the sensor. This means that the brighter the image at that point the larger of a value that is read for that pixel. Depending on the physical structure of the sensor a color filter array may be used which requires a demosaicing/interpolation algorithm. The number of resulting pixels in the image determines its "pixel count". For example, a 640x480 image would have 307,200 pixels, or approximately 307 kilopixels; a 3872x2592 image would have 10,036,224 pixels, or approximately 10 megapixels.

The pixel count alone is commonly presumed to indicate the resolution of a camera, but this is a misconception. There are several other factors that impact a sensor's resolution. Some of these factors include sensor size, lens quality, and the organization of the pixels (for example, a monochrome camera without a Bayer filter mosaic has a higher resolution than a typical color camera). Many digital compact cameras are criticized for having excessive pixels, in that the sensors can be so small that the resolution of the sensor is greater than the lens could possibly deliver.

As the technology has improved, costs have decreased dramatically. Measuring the "pixels per dollar" as a basic measure of value for a digital camera, there has been a continuous and steady increase in the number of pixels each dollar buys in a new camera consistent with the principles of Moore's Law. This predictability of camera prices was first presented in 1998 at the Australian PMA DIMA conference by Barry Hendy and since referred to as "Hendy's Law".

Since only a few aspect ratios are commonly used (especially 4:3 and 3:2), the number of sensor sizes that are useful is limited. Furthermore, sensor manufacturers don't manufacture every possible sensor size but take incremental steps in sizes. For example, in 2007 the three largest sensors (in terms of pixel count) used by Canon are the 21.1, 16.6, and 12.8 megapixel CMOS sensors. The following is a table of sensors commercially used in digital cameras.

Width	Height	Aspect ratio	Actual pixel count	Megapixels	Camera examples
320	240		76,800	0.1
640	480		307,200	0.3	Apple QuickTake 100 (1994)
832	608		505,856	0.5	Canon Powershot 600 (1996)
1,024	768		786,432	0.8	Olympus D-300L (1996)
1,280	960		1,228,800	1.3	Fujifilm DS-300 (1997)
1,280	1,024		1,310,720	1.5	Fujifilm MX-1700 (1999)
1,600	1,200		1,920,000	2	Nikon Coolpix 950
2,012	1,324		2,663,888	2.74	Nikon D1
2,048	1,536		3,145,728	3	Canon PowerShot A75
2,272	1,704		3,871,488	4	Canon Ixus 400
2,464	1,648		4,060,672	4.1	Canon 1D
2,560	1,920		4,915,200	5	Olympus E-1
2,816	2,112		5,947,392	6
3,008	2,000		6,016,000	6	Nikon D40, D50, D70, D70s
3,072	2,048		6,291,456	6.3	Canon 300D, Canon 10D
3,072	2,304		7,077,888	7	Olympus FE-210
3,456	2,304		7,962,624	8	Canon 350D
3,264	2,448		7,990,272	8	Olympus E-500,Olympus SP-350,Canon PowerShot A720 IS
3,504	2,336		8,185,344	8.2	Canon 30D, Canon 1D II, Canon 1D II N
3,520	2,344		8,250,880	8.25	Canon 20D
3,648	2,736		9,980,928	10	Olympus E-410, Olympus E-510, Panasonic FZ50
3,872	2,592		10,036,224	10	Nikon D40x, Nikon D200, Nikon D80, Sony Alpha A100
3,888	2,592		10,077,696	10.1	Canon 400D, Canon 40D
4,064	2,704		10,989,056	11	Canon 1Ds
4,256	2,832		12,052,992	12.1	Nikon D3
4,288	2,848		12,212,224	12.2	Nikon D2Xs/D2X,Nikon D300
4,368	2,912		12,719,616	12.8	Canon 5D
4,608	3,072		14,155,776	14.2	Sigma SD14
4,992	3,328		16,613,376	16.6	Canon 1Ds II
5,616	3,744		21,026,304	21.1	Canon 1Ds III
7,212	5,142		39,031,344	39.0	Hasselblad H3D-39