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PGF (Progressive Graphics File) is a wavelet-based bitmapped image format that employs lossless and lossy data compression. PGF was created to improve upon and replace the JPEG format. It was developed at the same time as JPEG 2000 but with a different focus: speed over compression ratio. A wavelet is a kind of mathematical function used to divide a given function into different frequency components and study each component with a resolution that matches its scale. ...
Suppose the smiley face in the top left corner is an RGB bitmap image. ...
It has been suggested that this article or section be merged into Comparison of graphics file formats. ...
Lossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. ...
A lossy data compression method is one where compressing data and then decompressing it retrieves data that may well be different from the original, but is close enough to be useful in some way. ...
In computing, JPEG (pronounced JAY-peg; IPA: ) is a commonly used standard method of compression for photographic images. ...
JPEG 2000 is a wavelet-based image compression standard. ...
PGF can operate at higher compression ratios without taking more encoding/decoding time and without generating the characteristic 'blocky and blurry' artifacts of the original DCT-based JPEG standard [1]. It also allows more sophisticated progressive downloads. A compression artifact (or artefact) is the result of an aggressive data compression scheme applied to an image, audio, or video that discards some data which is determined by an algorithm to be of lesser importance to the overall content but which is nonetheless discernible and objectionable to the user. ...
Color Models PGF supports a wide variety of color models: - grayscale with 1, 8, 16 or 31 bit per pixel
- RGB color image with 12, 16 (565), 24 or 48 bit per pixel
- ARGB color image with 32 bit per pixel
- L*a*b color image with 24 or 48 bit per pixel
- CMYK color image with 32 or 64 bit per pixel
In computing, a grayscale or greyscale digital image is an image in which the value of each pixel is a single sample. ...
The RGB color model utilizes the additive model in which red, green, and blue light are combined in various ways to create other colors. ...
RGBA color space stands for Red Green Blue Alpha. ...
CIE L*a*b* (CIELAB) is the most complete color model used conventionally to describe all the colors visible to the human eye. ...
Cyan, magenta, yellow, and key (black) CMYK (or sometimes YMCK) is a subtractive color model used in color printing. ...
Advantages There are several claimed advantages of PGF over the ordinary JPEG standard: - Superior compression performance: The image quality (measured in PSNR) for the same compression ratio is on average 3% better than the PSNR of JPEG. At lower bit rates (e.g. less than 0.25 bits/pixel for gray-scale images), PGF has a much more significant advantage over certain modes of JPEG: artifacts are less visible and there is almost no blocking. The compression gains over JPEG are attributed to the use of DWT.
- Multiple resolution representation: PGF provides seamless compression of multiple image components, with each component carrying from 1 to 31 bits per component sample. With this feature there is no need anymore for separately stored preview images (thumbnails).
- Progressive transmission by resolution accuracy, commonly referred to as progressive decoding: PGF provides efficient codestream organizations which are progressive by resolution. This way, after a smaller part of the whole file has been received, it is possible to see a lower quality of the final picture, the quality can be improved monotonically getting more data from the source.
- Lossless and lossy compression: PGF provides both lossless and lossy compression in a single compression architecture. Both lossy and lossless compression are provided by the use of a reversible (integer) wavelet transform.
- Side channel spatial information: it fully supports transparency and alpha planes.
The phrase peak signal-to-noise ratio, often abbreviated PSNR, is an engineering term for the ratio between the maximum value of a signal and the magnitude of background noise. ...
In numerical analysis and functional analysis, a discrete wavelet transform (DWT) is any wavelet transform for which the wavelets are discretely sampled. ...
The ThumbsPlus image file manager showing folder tree in the upper left and 12 thumbnail-size images to the right. ...
Technical discussion The aim of PGF is not only improved compression quality over JPEG but also adding (or improving) features such as scalability. In fact, PGF's improvement in compression performance relative to the original JPEG standard is actually rather modest and should not ordinarily be the primary consideration for evaluating the design. Moreover, very low and very high compression rates (including lossless compression) are also supported in PGF. In fact, the graceful ability of the design to handle a very large range of effective bit rates is one of the strengths of PGF. For example, to reduce the number of bits for a picture below a certain amount, the advisable thing to do with the first JPEG standard is to reduce the resolution of the input image before encoding it — something that is ordinarily not necessary for that purpose when using PGF because of its wavelet scalability properties.
The PGF process chain contains the following four steps:
A comparison of different color spaces. ...
In numerical analysis and functional analysis, a discrete wavelet transform (DWT) is any wavelet transform for which the wavelets are discretely sampled. ...
Quantization, involved in image processing. ...
This article does not cite its references or sources. ...
Run-length encoding (RLE) is a very simple form of data compression in which runs of data (that is, sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run. ...
Color components transformation Initially, images have to be transformed from the RGB color space to another color space, leading to three components that are handled separately. PGF uses a fully reversible modified YUV color transform. The transformation matrices are: A comparison of different color spaces. ...
 The chrominance components can be, but do not necessarily have to be, down-scaled in resolution. Chrominance (chroma for short) comprises the two components of a television signal that encode color information. ...
Wavelet transform The color components are then wavelet transformed to an arbitrary depth, in contrast to JPEG 1992 which uses an 8x8 block-size discrete cosine transform. PGF uses one reversible wavelet transform: a rounded version of the biorthogonal CDF 5/3 wavelet transform. This wavelet filter bank is exacetly the same as the reversible wavelet used in JPEG 2000. It uses only integer coefficients, so the output does not require rounding (quantization) and so it does not introduce any quantization noise. The wavelet transform is a transformation to basis functions that are localized in scale and in time as well (where the Fourier transform is only localized in frequency, never giving any information about where in space or time the frequency happens). ...
2-D DCT compared to the DFT The discrete cosine transform (DCT) is a Fourier-related transform similar to the discrete Fourier transform (DFT), but using only real numbers. ...
The historically first family of biorthogonal wavelets, which was made popular by Ingrid Daubechies. ...
A wavelet is a kind of mathematical function used to divide a given function into different frequency components and study each component with a resolution that matches its scale. ...
Quantization After the wavelet transform, the coefficients are scalar-quantized to reduce the amount of bits to represent them, at the expense of a loss of quality. The output is a set of integer numbers which have to be encoded bit-by-bit. The parameter that can be changed to set the final quality is the quantization step: the greater the step, the greater is the compression and the loss of quality. With a quantization step that equals 1, no quantization is performed (it is used in lossless compression). In contrast to JPEG 2000 PGF uses only powers of two, therefore the parameter value i represents a quantization step of 2i. Just using powers of two makes no need of integer multiplication and division operations. Generally, quantization is the state of being constrained to a set of discrete values, rather than varying continuously. ...
Coding The result of the previous process is a collection of sub-bands which represent several approximation scales. A sub-band is a set of coefficients — integer numbers which represent aspects of the image associated with a certain frequency range as well as a spatial area of the image. The integers are commonly denoted by the above symbol. ...
The quantized sub-bands are split further into blocks, rectangular regions in the wavelet domain. They are typically selected in a way that the coefficients within them across the sub-bands form approximately spatial blocks in the (reconstructed) image domain and collected in a fixed size macroblock.
The encoder has to encode the bits of all quantized coefficients of a macroblock, starting with the most significant bits and progressing to less significant bits. In this encoding process, each bit-plane of the macroblock gets encoded in two so-called coding passes, first encoding bits of significant coefficients, then refinement bits of significant coefficients. Clearly, in lossless mode all bit-planes have to be encoded, and no bit-planes can be dropped. This article does not cite its references or sources. ...
Only significant coefficients are compressed with an adaptive run-length/Rice (RLR) coder, because they contain long runs of zeros. The RLR coder with parameter k (logarithmic length of a run of zeros) is also known as the elementary Golomb code of order 2k. Run-length encoding (RLE) is a very simple form of data compression in which runs of data (that is, sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run. ...
Comparison with other File Formats
JPEG 2000 The JPEG 2000 is slightly more space-efficient in the case of natural images. The PSNR for the same compression ratio is on average 3% better than the PSNR of PGF. Its small advantage in compression ratio is paid with a clearly higher encoding and decoding time. JPEG 2000 is a wavelet-based image compression standard. ...
The phrase peak signal-to-noise ratio, often abbreviated PSNR, is an engineering term for the ratio between the maximum value of a signal and the magnitude of background noise. ...
The original PGF source code is open (not patented) and available under LGPL. GNU logo The GNU Lesser General Public License (formerly the GNU Library General Public License) is an FSF approved Free Software license designed as a compromise between the GNU General Public License and simple permissive licenses such as the BSD license and the MIT License. ...
PNG The PNG (Portable Network Graphics) format is still more space-efficient in the case of images with many pixels of the same color. It can be expected that PNG will be more heavily used for compressing diagram-type images and PGF for photograph-type images. PNG (Portable Network Graphics) is a bitmapped image format that employs lossless data compression. ...
References - ^ PGF - A new progressive file format for lossy and lossless image compression
See also It has been suggested that Graphics file format summary be merged into this article or section. ...
See also Category:Graphics file formats Here is a summary of the most common graphics file formats: Some file formats, e. ...
JPEG 2000 is a wavelet-based image compression standard. ...
In computing, JPEG (pronounced JAY-peg; IPA: ) is a commonly used standard method of compression for photographic images. ...
Image file formats provide a standardized method of organizing and storing image data. ...
Image compression is the application of data compression on digital images. ...
External links - PGF Home Site
- xeraina Image Viewer – Image viewer and converter for most popular image formats including PGF (freeware for non-commercial usage)
Multimedia Compression Formats (See Compression Methods for methods and Compression Software Implementations for codecs) ...
In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits (or other information-bearing units) than an unencoded representation would use through use of specific encoding schemes. ...
Video compression refers to making a digital video signal use less data, without noticeably reducing the quality of the picture. ...
This article does not cite any references or sources. ...
The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ...
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This article does not cite any references or sources. ...
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The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland. ...
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G.722. ...
Adaptive Multi Rate - WideBand or AMR-WB is a speech coding standard developed after the AMR using same technology like ACELP. The codec provides excellent speech quality due to wider speech bandwidth of 50 - 7000 Hz compared to narrowband speech codecs which in general are optimized for POTS wireline quality...
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G.723. ...
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The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...
G.729 is an audio data compression algorithm for voice that compresses voice audio in chunks of 10 milliseconds. ...
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This article does not cite any references or sources. ...
The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ...
The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland. ...
In computing, JPEG (pronounced JAY-peg; IPA: ) is a commonly used standard method of compression for photographic images. ...
JPEG 2000 is a wavelet-based image compression standard. ...
The Joint Photographic Experts Group, in addition to their well-known lossy image compression techniques, JPEG and JPEG 2000, also have three standards for lossless compression (of which JPEG-LS has a lossy mode): Lossless JPEG was developed as a late addition to JPEG in 1993, using a completely different...
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Wireless Application Protocol Bitmap Format (shortened to Wireless Bitmap and with file extension . ...
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.BMP or . ...
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“TIFF†redirects here. ...
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