Image Formats: GIF - JPEG - PNG - JPEG 2000 - Facts / pro / con
For lossy compression to reduce file size, use JPEG. For everything else
(includeing archive storage of photographic images prior to JPEG compress),
use PNG. Use GIF for simple animation. JPEG 2000 refers to all parts of
the standard are still under development.
Common Image Formats Support by most Web Browser and their Features and Benefits
|Feature||GIF||JPEG||PNG||JPEG 2000 (JP2)|
|Lossless compression||y||N||Y||Can be|
|RGB support (Max bits-per-pisel)||N(--)||Y(24)||Y(48)||Y(48)|
|Animation support||Y||N||N||JPX, MJ2|
- Compression: Compresses by scanning horizontally across a row of pixels and finding solid areas of color. Indexes the pixels based on the 256 color palette in the file. No image information is lost. Note: some information may be lost in the conversion process from RGB to GIF format.
- Best for: Images with repetitive areas of solid color, line drawings, screenshots, sharp images. Ideal for cartoon-like graphics, logos, graphics with transparent areas, and animations. Excels at condensing graphical images with areas of flat color.
- Colors Supported: Contains only 256 colors (8-bit). Can contain a transparent area and multiple frames for animation.
- Downloads using: Interlacing, which uses the same technique for downloading as JPEG's progressive encoding. An interlaced GIF displays images in two passes of alternating lines instead of loading them one line at a time. The viewer begins to see the outline of the image sooner with interlacing.
- Browser Support: First graphic file type to be displayed by the early web browsers. The only graphic file formate that is universally supported by all graphical browsers, regardless of version. Most popular and versatile format for distributing color image on the Web.
- Other Issues: Any image can be saved as a GIF and the files are completely platform independent. The company holding the patent on the LZW compression model used in GIFS, has started to enforce the patent and charge software companies fees for including GIF support. This action led to the development of PNG.
- Compression: Some image data is discarded when it is compressed, reducing the quality of the final file. The compression algorithms handle sharp edges and abrupt changes poorly. Does not use palettes for referencing color information. In General, a JPEG will compress a photographic image 2-3 times smaller than GIF. You can choose how much to compress a JPEG file, but since it is a lossy format, the smaller you compress the file, the more color information will be lost.
- Best for: Scanned photographs, images using textures, images with gradient color transitions or any images that require more than 256 colors. It is generally best to let JPEGs handle photographic material and to leave the graphics to GIF.
- Colors Supported: Supports millions of colors (24-bit).
- Downloads using: Can download using progressive encoding: This technique downloads a rough whole image and gradually increases the image's clarity, instead of downloading from the top of the image and moving downward as is done normally. Requires more processing power to display. If the browser does not support progressive encoding, the images loads from top to bottom.
- Browser Support: Fully supported for use as inline images in version 2.0 and higher of Netscape Navigator and Internet Explorer, as well as in most other current browsers.
- Other Issues: Need to be decompressed before they can be displayed; therefore, it takes a browser longer to decode and assemble a JPEG than a GIF of the same file size.
- Compression: Compresses across rows and columns of pixels, often yielding better compression than GIF, which only scans rows. The compression is 'lossless', you do not lose color information as you compress the file smaller. Typically compresses images 5-25% better than GIF.
- Best for: Creating complex live transparency, high-color graphics, and better compressed low-color graphics.
- Colors Supported: Can support up to 8-bit palette indexed color, 16-bit grayscale images, 48-bit truecolor. Can contain transparency or an alpha channel, and can be progressive.
- Downloads using: A more sophisticated interlacing technique than GIF and starts displaying the image in 1/8th the time.
- Browser Support: The most versatile of the Web graphic formats, however not all Web browsers can currently take full advantage of PNG characteristics without using plug-ins.
- JP2 is the file extension for the new image format called JPEG2000
based on state-of-the-art wavelet compression. The compression ratio
is better than JPEG which use a scheme called discrete cosine transformation.
The wavelet compression uses mathematical expressions to encode the
image in a continuous stream, the result can be completely lossless
and yet produce extremely small files.
Loseless compression, meaning the decompressed image data is exactly as it was before compression.
- The JPEG2000 architecture advances a number of different applications in the digital imaging market, everything from digital cameras, pre-press, medical imaging and other key sectors.
- There are 4 progressive display methods:
1. Quality Axis, image starts blurred
2. Resolution Axis, image is loaded as a smaller version
3. Color Axis, image starts loading as a grayscale image
4. Position Axis, image is loades as blocks
As more image data is received, the sharpness or size, or color or blocks is getting better.
- Other Issues: Designed to be network-friendly, so it is recognized and supported on all platforms. Supports both indexed and truecolor image types, so there's no bitmapped graphic it can't handle. For Web purposes where every byte counts, photographic and continuous tone images are still best saved as JPEGs. The better compression engine results in a smaller file size than GIF for the same image.
- With JPEG 200 extensions, there is a new file format, JPX, based on JP2 but supporting multiple compositing layers, animation, extended colour spaces and more
- MJ2 (or MJP2) for motion sequences of JPEG 2000 images, does not involve
inter-frame coding: each frame is coded independently using JPEG 2000.
Expected applications include:
- storing video clips taken using digital still cameras
- high-quality frame-based video recording and editing
- digital cinema
- medical and satellite imagery
- JPM file format for document imaging is an extension of the JP2 file format, can be used to store multi-page documents with many objects per page.
- JPEG 2000 Secured (JPSEC), will provide a flexible mechanism to allow for encryption of image content and metadata and other security issues. The underlying techniques to protect the content include digital signatures, watermarking, encryption, scrambling, and key generation and management.
- JPIP is supporting image and metadata delivery in a networked environment
- JP3D is concerned with the coding of three-dimensional data
- 2000 Wireless (JPWL) is standardising tools and methods to achieve the efficient transmission of JPEG 2000 imagery over an error-prone wireless network.