Megapixel , based on the SI prefix, stands for one million image points ( pixels ), which corresponds to a square image with a height and width of 1024 pixels each. It is the common unit for specifying the sensor and image resolution in digital photography . For a long time, this number was largely the only criterion for evaluating a digital camera in advertising .
A uniform abbreviation has not yet become established, both “MP” and “Mpx”, “Mpix” and “MPixel” are common. To specify the physical resolution, camera manufacturers count each colored (sub) pixel individually, i.e. each red, blue or green (sub) sensor of a sensor. The number of pixels in a camera is therefore not the same as the number of pixels on a screen . Higher image resolutions enable larger-format photo prints, as the number of pixels per area is greater, i.e. the grid is smaller. The physical pixels of the image sensor are decisive for the image quality , not those artificially calculated by interpolation .
The following criticism of more pixels with the same sensor area relates almost exclusively to a comparison with different sections or enlargements of the image. The mentioned points of criticism cannot be maintained with identical magnification.
Most digital cameras have changed in two main ways in recent years. On the one hand, the number of pixels has now mostly increased to 24 megapixels (as of 2017; well over ten megapixels, as of the end of 2008; approx. 14 megapixels, as of the end of 2010, approx. 16 megapixels, as of 2015); on the other hand, the image sensors became smaller and smaller. In the years from 2005 to 2010, the size of the image sensors halved from around 60 mm² to 30 mm², while the overall resolution increased fourfold - the individual pixels were only an eighth of the size they were five years earlier. However, since incorrect information in relation to the actual image information has a stronger effect on a smaller area, so-called image noise occurs . This becomes a problem especially with higher exposure indicators (analogous to the earlier film speeds ) or with dark image areas. This problem is particularly important with a 1: 1 view when you zoom in significantly closer to the image compared to an image from a lower-resolution camera. If the output is the same size, the problem is evened out because the misinformation is distributed over several pixels. In order to circumvent this problem, even with large output formats, modern cameras are increasingly using noise suppression processes that attempt to correct these image errors at the expense of image sharpness or loss of detail. However, very small pixel sizes limit the freedom in choosing the f-number if one expects very good results with enlargement in the 1: 1 view; in addition, if the pixels are too small, interference from diffraction of light is more noticeable at corresponding enlargements.
The advantage of a high resolution, however, is a lower sensitivity for the moiré effect and the possibility of creating smaller sections with sufficient resolution, especially in cameras with the usual Bayer sensor .
In contrast to this, digital system cameras mainly use larger sensors (often APS-C with around 350 mm²) which, with a resolution of 37 megapixels, would have a pixel size that would, for example, correspond to today's compact cameras with only three megapixels. Noise is often not as pronounced with these cameras as with models with smaller sensors. With an increasing number of pixels beyond 20 megapixels and different equipment variants, general statements regarding the noise behavior are not possible. With the same number of megapixels, larger sensors have an advantage due to their design in terms of image noise, but at the expense of the depth of field . With the same depth of field, you have to stop down, which reduces the incidence of light and usually increases the sensor sensitivity. However, this is again associated with an increase in noise. However, especially with a very large number of pixels, the image noise at the pixel level is no longer recognizable in the overall image, as the playback media, such as screens or prints , as well as the human retina are not able to resolve so many individual pixels that interpolation is carried out accordingly , whereby the artifact is distributed.
Large image sensors (mostly 1 inch sensors) are also used in a few compact cameras in the upper price ranges.
A middle ground is the so-called Micro Four Thirds standard , in which an image sensor with the size designation 4/3 "and an area of approximately 225 mm² is used. This should enable the production of comparatively small and light cameras with nevertheless low-noise images .
A similar trend can be observed with video cameras . The number of pixels increases only insignificantly here, but the image sensors of non-professional cameras are getting smaller and smaller in order to get ever larger zoom ranges from consistently compact and inexpensive lenses.
Size comparison of common resolutions
- DXOmark page with practical results of different sensor sizes and sensor resolutions with the same output format
- ↑ Digital Photography: The Breakthrough in Image Quality? , test.de , March 21, 2013, accessed online on April 15, 2013 (paywall).
- ↑ Camera: Pixel not everything , test.de , November 16, 2006, accessed online on April 15, 2013.
- ↑ 6MPixel.org - Overview of high resolution problems .