The following compression mechanisms can be used in a PDF document:
|
Mechanism |
Description |
|---|---|
|
JPEG |
The JPEG compression method is best suited for grayscale or color bitmap images. A typical example of an image for which JPEG compression is advised is a continuous-tone photograph. This type of image contains more information, more details, than can be reproduced on screen or in print. Therefore, it makes sense to remove the information that cannot be displayed anyway. This can result in a loss of image quality, as the compression method removes information: it is called a lossy reduction method. However, file sizes are greatly reduced by JPEG compression. |
|
ZIP |
The ZIP compression method is best suited for vector graphics (line art), and images that contain large areas of a single color, or repeating patterns. Typical examples of this kind of images include screen shots and simple graphics. ZIP compression is lossless, which means that no information is removed from the image during compression. |
|
LZW |
The LZW compression discovers and exploits many patterns in images or text (by using a differencing technique, for example). In general, high compression rates can be achieved with this compression algorithm. |
|
RunLength |
The RunLength compression method is best suited for images that contain large areas of solid white or black. It is a lossless compression method, which means that no information is removed from the images during compression. |
|
JBIG |
The JBIG compression method is best suited for black-and-white images, but it can also be used for coding grayscale and color images with limited numbers of bits per pixel. It is a lossless compression method, which means that no information is removed from the images during compression. |
|
CCITT |
The CCITT compression method is best suited for black-and-white images made by paint programs, as well as for images scanned with an image depth of 1 bit. CCITT is a lossless compression method, which means that no information is removed from the images during compression. |
|
JPEG2000 |
The JPEG2000 compression method is suitable for any kind of image and gives somewhat better size reduction than other methods. The quality range can vary from strong lossy to lossless compression. In addition, JPEG2000 provides new features such as transparency, color components with different number of bits per sample, and the possibility to decode versions of the image that differ in sampling resolution and other factors. |