Color Cell Compression
Encyclopedia
Color Cell Compression is an early lossy image compression
algorithm first described by Campbell et. al. in 1986. It is a variant of Block Truncation Coding
. The encoding process works on small blocks of pixel
s. For each block, it first partitions the pixels in that block into to two sets based on their luminance
values, then generates representative colour values for each of these sets, and a bitmap
that specifies which pixels belong to which set. The two colour values and the bitmap for each block are then output directly without any further quantization
or entropy coding.
The decoding process is simple; each pixel of an output block is generated by choosing one of the two representative colours for that block, based on that block's bitmap.
In spite of its very simple mechanism, the algorithm yields surprisingly good results on photographic images, and it has the advantage of being very fast to decode with limited hardware. Although far surpassed in compression ratio by later block-transform coding methods such as JPEG
, it had the advantage of very simple decompression and fast random access into the compressed image, and it can be regarded as a forerunner of modern texture compression
algorithms.
Image compression
The objective of image compression is to reduce irrelevance and redundancy of the image data in order to be able to store or transmit data in an efficient form.- Lossy and lossless compression :...
algorithm first described by Campbell et. al. in 1986. It is a variant of Block Truncation Coding
Block Truncation Coding
Block Truncation Coding, or BTC, is a type of lossy image compression technique for greyscale images. It divides the original images into blocks and then uses a quantiser to reduce the number of grey levels in each block whilst maintaining the same mean and standard deviation...
. The encoding process works on small blocks of 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....
s. For each block, it first partitions the pixels in that block into to two sets based on their luminance
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
values, then generates representative colour values for each of these sets, and a bitmap
Bitmap
In computer graphics, a bitmap or pixmap is a type of memory organization or image file format used to store digital images. The term bitmap comes from the computer programming terminology, meaning just a map of bits, a spatially mapped array of bits. Now, along with pixmap, it commonly refers to...
that specifies which pixels belong to which set. The two colour values and the bitmap for each block are then output directly without any further quantization
Quantization
Quantization is the procedure of constraining something from a relatively large or continuous set of values to a relatively small discrete set...
or entropy coding.
The decoding process is simple; each pixel of an output block is generated by choosing one of the two representative colours for that block, based on that block's bitmap.
In spite of its very simple mechanism, the algorithm yields surprisingly good results on photographic images, and it has the advantage of being very fast to decode with limited hardware. Although far surpassed in compression ratio by later block-transform coding methods such as JPEG
JPEG
In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
, it had the advantage of very simple decompression and fast random access into the compressed image, and it can be regarded as a forerunner of modern texture compression
Texture compression
Texture compression is a specialized form of image compression designed for storing texture maps in 3D computer graphics rendering systems. Unlike conventional image compression algorithms, texture compression algorithms are optimized for random access....
algorithms.