Image processing engine
Encyclopedia
The image processing engine, or image processor, is an important component of a digital camera
. The digital image
processing engine can perform a range of tasks.
s employed in an image sensor
are colour-blind by nature: they can only record shades of grey. To get colour into the picture, they are covered with different colour filters: red, green and blue (RGB) according to the pattern designated by the Bayer filter
- named after its inventor. As each photodiode records the colour information for exactly one pixel
of the image, without an image processor there would be a green pixel next to each red and blue pixel. (Actually, with most sensors there are two green for each blue and red diodes.)
This process, however, is quite complex and involves a number of different operations. Its success depends largely on the "intelligence" of the algorithms applied.
algorithm to produce an appropriate colour and brightness value for the pixel. The image processor also assesses the whole picture to guess at the correct distribution of contrast. By adjusting the gamma
value (heightening or lowering the contrast range of an image's mid-tones) subtle tonal gradations, such as in human skin or the blue of the sky, become much more realistic.
is a phenomenon found in any electronic circuitry. In digital photography its effect is often visible as random spots of obviously wrong colour in an otherwise smoothly-coloured area. Noise increases with temperature and exposure times. When higher ISO settings are chosen the electronic signal in the image sensor is amplified, which at the same time increases the noise level, leading to a lower signal-to-noise ratio
. The image processor attempts to separate the noise from the image information and to remove it. This can be quite a challenge, as the image may contain areas with fine textures which, if treated as noise, may lose some of their definition.
correctly and reproduce them smoothly and without over-sharpening.
Individual manufacturers have named their image processing engines differently: Canon's is called DIGIC, Nikon's EXPEED, Olympus' TruePic
, and Panasonic's the VENUS Engine
.
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
. The digital image
Digital image
A digital image is a numeric representation of a two-dimensional image. Depending on whether or not the image resolution is fixed, it may be of vector or raster type...
processing engine can perform a range of tasks.
Bayer transformation
The photodiodePhotodiode
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area photodiode....
s employed in an image sensor
Image sensor
An image sensor is a device that converts an optical image into an electronic signal. It is used mostly in digital cameras and other imaging devices...
are colour-blind by nature: they can only record shades of grey. To get colour into the picture, they are covered with different colour filters: red, green and blue (RGB) according to the pattern designated by the Bayer filter
Bayer filter
A Bayer filter mosaic is a color filter array for arranging RGB color filters on a square grid of photosensors. Its particular arrangement of color filters is used in most single-chip digital image sensors used in digital cameras, camcorders, and scanners to create a color image...
- named after its inventor. As each photodiode records the colour information for exactly one pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
of the image, without an image processor there would be a green pixel next to each red and blue pixel. (Actually, with most sensors there are two green for each blue and red diodes.)
This process, however, is quite complex and involves a number of different operations. Its success depends largely on the "intelligence" of the algorithms applied.
Demosaicing
As stated above, the image processor evaluates the colour and brightness data of a given pixel, compares them with the data from neighbouring pixels and then uses a demosaicingDemosaicing
A demosaicing algorithm is a digital image process used to reconstruct a full color image from the incomplete color samples output from an image sensor overlaid with a color filter array...
algorithm to produce an appropriate colour and brightness value for the pixel. The image processor also assesses the whole picture to guess at the correct distribution of contrast. By adjusting the gamma
Gamma correction
Gamma correction, gamma nonlinearity, gamma encoding, or often simply gamma, is the name of a nonlinear operation used to code and decode luminance or tristimulus values in video or still image systems...
value (heightening or lowering the contrast range of an image's mid-tones) subtle tonal gradations, such as in human skin or the blue of the sky, become much more realistic.
Noise reduction
NoiseImage noise
Image noise is random variation of brightness or color information in images, and is usually an aspect of electronic noise. It can be produced by the sensor and circuitry of a scanner or digital camera...
is a phenomenon found in any electronic circuitry. In digital photography its effect is often visible as random spots of obviously wrong colour in an otherwise smoothly-coloured area. Noise increases with temperature and exposure times. When higher ISO settings are chosen the electronic signal in the image sensor is amplified, which at the same time increases the noise level, leading to a lower signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
. The image processor attempts to separate the noise from the image information and to remove it. This can be quite a challenge, as the image may contain areas with fine textures which, if treated as noise, may lose some of their definition.
Image sharpening
As the color and brightness values for each pixel are interpolated some image softening is applied to even out any fuzziness that has occurred. To preserve the impression of depth, clarity and fine details, the image processor must sharpen edges and contours. It therefore must detect edgesEdge detection
Edge detection is a fundamental tool in image processing and computer vision, particularly in the areas of feature detection and feature extraction, which aim at identifying points in a digital image at which the image brightness changes sharply or, more formally, has discontinuities...
correctly and reproduce them smoothly and without over-sharpening.
Speed
With the ever higher pixel count in image sensors, the image processor's speed becomes more critical: photographers don't want to wait for the camera's image processor to complete its job before they can carry on shooting - they don't even want to notice some processing is going on inside the camera. Therefore, image processors must be optimised to cope with more data in the same or even a shorter period of time.Individual manufacturers have named their image processing engines differently: Canon's is called DIGIC, Nikon's EXPEED, Olympus' TruePic
TruePic
TruePic is the name Olympus has given its image processing engine. The second version was named TruePic TURBO. In 2007 Olympus began to equip its digital cameras, both compact and D-SLRs with the latest version, TruePic III.TruePic III...
, and Panasonic's the VENUS Engine
Venus Engine
The Venus processing engine for digital cameras is an image processing engine developed by Panasonic, and almost all of their Lumix cameras use a version of it. Image processors operate in four steps: receive data from the CCD sensor, create the Y-color difference signal , perform JPEG compression,...
.
See also
- Color image pipelineColor image pipelineAn image pipeline or video pipeline is a term used to describe the components that are typically or commonly used between an image source , and an image renderer , or for performing any intermediate digital image processing...
- Image processingImage processingIn electrical engineering and computer science, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame; the output of image processing may be either an image or, a set of characteristics or parameters related to the image...
- Digital image processingDigital image processingDigital image processing is the use of computer algorithms to perform image processing on digital images. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing...
- Digital image editing
- DemosaicingDemosaicingA demosaicing algorithm is a digital image process used to reconstruct a full color image from the incomplete color samples output from an image sensor overlaid with a color filter array...