#IMAGE COMPRESSION STANDARDS ISO#

Although JPEG 2000 has a lossless mode, specific standards, like JPEG-LS (JPEG-LS, 1997), offer better performance. If it is important to recover exactly the original image, for example, for legal reasons in medical imaging or in image editing, lossless compression can be done at the cost of lower compression performance (but no quality loss). It is important to emphasise that the comparison of lossy encoders cannot be performed based on the final image size alone, but also on its visual quality, in a sort of cost/benefit ratio (usually represented as a rate/distortion curve). This type of image coding process, where recovered data is not the encoded one, is called lossy compression. However, the higher complexity of JPEG 2000 and the current widespread use of JPEG make the success of this new version uncertain in the mass market. An evolution from this standard is the new JPEG 2000 standard (JPEG 2000, 2000), based on the same ideas, which is more efficient and flexible.

Although the decompressed image is not equal to the original one if compared pixel by pixel, the perceptual quality could be nearly the same, provided that no heavy compression is applied.

Its sequential mode, widely used throughout the entertainment industry, is based on removing information that is hardly perceived by a human viewer (in particular, high-frequency components are less accurately encoded). The well-known standard, JPEG (JPEG, 1992), focuses on this type of image. Actually, for colour images, three bytes per pixel are commonly used (one byte per colour component, red, green, and blue, which is known as RGB colour space), where each pixel represents a colour from up to 2 24 possibilities. In addition, the authors review the JBIG standard, which aims at binary image coding, being widely used for fax transmission.įor continuous tone images (e.g., those from a digital camera), each pixel takes a value in a (nonbinary) range typically any value in the range for a greyscale image.

#IMAGE COMPRESSION STANDARDS ISO#

For continuous-tune still-image lossy compression, the chapter reviews the classic ISO JPEG standard and the newer ISO JPEG 2000, while for lossless compression, the ISO JPEG-LS is presented. The main contribution of this chapter is a brief survey on ISO standards for image coding. Fortunately, most images are characterized by highly redundant signals (especially natural and synthetic images), since pixels composing an image present high homogeneity, and this redundancy, often called spatial redundancy, can be reduced through a compression process, achieving a more compact representation. In general, in order to exploit the information system resources in an efficient way when dealing with images, compression is almost mandatory. Thus, there was a clear urge to reduce the amount of bytes required to encode an image, mainly so as to avoid an excessive increase in both memory consumption and network bandwidth required to store and transmit images, which would limit or prevent their use in practice. Although images made more pleasant the interaction with computers, their use represented a new challenge for electronic engineers while only a few bytes are needed to represent a text (typically one byte per character in extended ASCII), lots of data must be employed for images that, in a “raw” representation (i.e., uncompressed) for colour images, need as many as three bytes per single pixel (picture element, each dot forming an image). Later on, the multimedia era arrived, with personal computers and other devices having powerful graphic capabilities, plenty of full-coloured pictures shown to the user. AbstractOnly a few decades ago, the human-computer interaction was based on a rudimentary text user interface, a convenient method compared to the punch card era, but too tedious and not very appealing for the nonspecialist, and thereby, not suitable for the mass market.

Image compression standards