Home  PDF-Tools  Document  Support

JPEG2000 compression Advanced PDF Tools v2.0

JPEG2000 compression overview

PDF supports a number of industry-standard compression filters that reduce file size by eliminating unnecessary pixel data. There are many kinds of compression methods, such as JPEG, JPEG2000 (in PDF 1.5), CCITT, JBIG2, ZIP, Flate ,etc., which are included in PDF applications, e.g. Advanced PDF Tools v2.0.

Advanced PDF Tools v2.0 is a professional PDF edit tool, including image compressing, optimizing, page scaling and so on. To reduce PDF file size, it uses JPEG, JPEG2000, Flate, CCITT G4 compression algorithms, where JPEG2000 algorithm, embodied by IS 15444-1, is fundamentally different from the earlier JPEG algorithm, imparting the new standard with higher compression efficiency and, most significantly, enhanced flexibility for distribution of and interaction with the compressed content, so we willingly introduce it first to you.

JPEG2000 features

Before we get to JPEG2000, we'd first get to know JPEG, because JPEG2000 is the latest algorithm from the JPEG normalization group for still picture compression.

• JPEG

JPEG (Joint Photographic Experts Group) is an compression algorithm suitable for grayscale or color images, such as continuous-tone photographs that contain more detail than can be reproduced on-screen or in print. JPEG is lossy, which means that it removes image data and may reduce image quality, but it attempts to reduce file size with the minimum loss of information. It can achieve much smaller file sizes than ZIP compression.

• JPEG2000

JPEG2000 is the latest series of standards from the JPEG committee. The original standard for digital images (IS 10918-1, popularly referred to as JPEG) was developed 15 years ago, and with the major increase in computer technology since them, and lots of research, it was felt to be time for a new standard capable of handling many more aspects than simply making the digital image files as small as possible. It has the following features:

• JPEG2000 uses wavelet technology.
• JPEG2000 compression give better results on images (up to 20 per cent plus) like photographs with gradual transitions from color to color.
• It can allow an image to be retained without any distortion or loss. Simply sending the first part of such a lossless file to a receiver can result in a lossy version appearing (like present JPEG) - but continuing to transmit the file results in the fidelity getting better and better until the original image is restored.
• PEG and JPEG2000 compression methods are typically lossy, a process that permanently removes some pixel data. You can apply lossy JPEG or JPEG2000 compression to color images at various levels (minimum, low, medium, high, maximum).
• For JPEG2000 compression, you can also specify lossless so that no pixel data is removed. Compression for monochrome images is lossless, except for JBIG2 compression, which provides both lossy and lossless modes of compression.

JPEG2000 algorithm introduction

Although JPEG2000 is based on a single algorithm, it offers a wide range of tools for compressing and representing images. It is suitable for a large spectrum of applications ranging from Internet streaming to medical imaging to digital cameras.

JPEG2000 encompasses some separate algorithms including:

• Lossy and lossless compression with excellent performance
• Precise compression ratio control with single-pass processing
• Bitstream progressivity, allowing consistent image previews with partial bitstream decoding
• Support for user-defined regions of interest in the image, encoded with higher quality than the other areas
• Error resilience.

Stage 1: DWT-Based Compression
The JPEG2000 algorithm divides the image into rectangular tiles of a configurable size.

Each tile undergoes a two-dimensional discrete wavelet transform (DWT), which reorders the tile s frequency information into a series of pictures (subbands). A subband results from the filtering of the original tile for a given frequency range.

A parameter of the transform (the number of decomposition levels) defines the number of frequency intervals.

Each subband can then undergo selective quantization by a programmable factor for lossy compression. Bypassing the quantization yields lossless operation.

The algorithm further divides the resulting quantized subbands into smaller rectangular blocks (code blocks).

A modeler examines the bit planes of the current code block, beginning with the most significant one. In each plane, it scans the bits in a zigzag order and determines their context by using information such as the predominant value of the surrounding bits.

Finally, an arithmetic encoder processes the value of the bit and the context. It generates a code stream representing the compressed code block.

This arithmetic encoder also computes distortion metrics, which reflect the image distortion that would be encountered when reconstructing the code block with its currently encoded portion.

Stage 2: Packet Selection and Reordering
The code stream generated by the arithmetic encoder, together with the distortion metrics, allows JPEG2000 to selectively build the final bitstream at the post-processing stage. This process is driven by two user-defined parameters:

• Compression ratio  Stage 2 selects incoming packets to attain a user-specified compression ratio. The algorithm rejects packets that do not sufficiently improve the compression distortion. This mechanism allows precise control of the generated compressed file size, while maintaining good image quality.
• Progression order  JPEG2000 allows an initial preview of a picture with the first portion of the bitstream. Decoding subsequent parts of the compressed file progressively refines the image. JPEG2000 also standardizes various refinement orders by prioritizing an image characteristic, such as quality or resolution. Stage 2 achieves the desired progression order by reordering incoming packets.

JPEG2000 compression method, an international standard for the compression and packaging of image data. JPEG2000 defines a wavelet-based method for image compression that gives somewhat better size reduction than other methods such as regular JPEG or CCITT. Although the method can reproduce samples that are losslessly compressed, it is recommended only for use with images and not for general data compression.

JPEG2000 in Advanced PDF Tools

JPEG2000 compression is one of the features of Advanced PDF Tools. The color image, gray image or monochrome image can be compressed by choosing an algorithm from the image panel on Advanced PDF Tools GUI version. With this tool, the image compressing quality and the scale ratio to the image can be set if you need. JPEG2000 is mainly used to compress the color image.

You can also use the PDF compress command line tool, which is Advanced PDF Tools command line version, to set the compression. For example, you can write a configuration file "compress.ini" in "C:\Program Files\Advanced PDF Tools v2.0\compress.ini".

[colorimage]
compressformat=3
quality=80
imagesize=94

And in the command window input the following command

pdfcompress -i C:\input.pdf -o C:\output.pdf     

Then the input.pdf file can be changed to output.pdf with its color image compressed by the format JPEG2000 compression. The compressformat value can be 0, 1, 2 and 3. 0 stands for Not change, 1 stands for  Flate compression, 2 stands for JPEG compression and 3 stands for JPEG2000 compression.

For the JPEG2000 compression SDK, COM, Library etc. developer components, please ask to support@verypdf.com.

Advanced PDF Tools Command Line Home page.

Copyright © 2000-2006 by VeryPDF.com, Inc.
Send comments about this site to the webmaster.