Image Formats
From GDWiki
Different image formats have different strong and weak points; it is important to be aware of these in order to chose the right format for the task at hand.
Contents |
[edit] Raster Formats
[edit] General Information
The below table exists to compare various common raster image formats. Please note that not all image formats are present in this table.
| RGB | RGBA | Grayscale | Indexed | HDR | Animation | Compression | Free | Extensible | |
|---|---|---|---|---|---|---|---|---|---|
| BMP | 24-bit | No | 8-bit | Yes | No | No | lossless (RLE) | Yes | No |
| DDS | 24-bit | 32-bit | No | No | No | No | lossy (S3TC/DXTn) | No [1] | No |
| GIF | No | No | 8-bit | Yes | No | Yes | lossless (RLE) | Yes [2] | No |
| JPEG | 24-bit | No | No | No | No | No [3] | lossy (DCT) | Yes [4] | No |
| JPEG 2000 | 24-bit, 48-bit | 32-bit, 64-bit? | 8-bit, 16-bit | No | No | No | various | No [5] | ? |
| PCX | No | No | 8-bit | Yes | No | No | lossless (RLE) | Yes? | No |
| PNG | 24-bit, 48-bit | 32-bit, 64-bit | 8-bit, 16-bit | Yes | No | No [6] | lossless (deflate) | Yes | Yes |
| TGA | 24-bit | 32-bit | Yes | Yes | No | No | lossless (RLE) [7] | Yes | No |
| TIFF | 24-bit+ | 32-bit+ | Yes | Yes | Yes | No | various | Yes? | Yes |
- There are current patents on the S3TC compression techniques; as such, it is illegal to implement S3TC/DXTn compression without a license. Keep in mind, however, that video card vendors have already obtained this license to decompress S3TC/DXTn in hardware; so long as you do not compress/decompress in your own code, you do not need a license.
- Originally, the compression used by GIF was patented by Unisys, preventing free use. Since August, 2004, however, all relevant patents have exipred (see Unisys and LZW patent enforcement on Wikipedia.)
- There is a related format called "Motion JPEG" used for video files; however, this is not directly part of the JPEG format itself.
- There have been various patents asserted over JPEG in its lifetime, although all known patents have either expired or been ruled invalid. That said, as a widely used, popular image format, there may yet be submarine patents that have not yet come to light.
- Whilst the core parts of JPEG 2000 are stated to be freely implementable, many advanced features require licensing fees to implement.
- There are two standards which provide an animated PNG-style format: MNG and APNG. MNG is a relatively large, complex standard that has not seen wide adoption but is championed by the creators of PNG. APNG is a simple modification to the standard PNG format to support multiple frames, and has found support from several web browser vendors.
- TGA optionally supports RLE compression, although it is commonly used without compression at all.
- Explanation of columns
- RGB
- format support for direct RGB color, and in what bit-depth(s).
- RGBA
- format support for direct RGBA color, or RGB plus an alpha mask, and in what bit-depth(s).
- Grayscale
- format support for grayscale images, and in what bit-depth(s).
- Indexed
- does the format support 8-bit indexed (or paletted) images.
- HDR
- can the format store High Dynamic Range (a.k.a. floating-point) image data?
- Animation
- does the format support sequenced frame animation or better?
- Compression
- what, if any, compression method(s) does the format use?
- Free
- is the format free of patents and/or licensing fees?
- Extensible
- can additional information be attached to images whilst retaining compatibility with existing tools?
[edit] BMP
Pros:
- Widely supported.
Cons:
- Produces large files.
- Does not support alpha transparency.
[edit] DDS
Pros:
- Native format for S3TC/DXTn compression—compressed image data can be uploaded directly to video card memory.
- Supports other features like cube maps, mip maps, etc.
Cons:
- Compression format is patented, requiring a license to compress or decompress outside of hardware.
- No support for lossless compression.
[edit] GIF
Pros:
- Supports animation.
Cons:
- Very low visual quality.
- For still images of identical quality, PNG is always smaller.
[edit] JPEG
Pros:
- Good lossy compression.
- Widely supported and implemented—there are a number of freely available libraries for it.
Cons:
- Can produce noticeable compression artifacts.
- Is not natively supported by video cards.
- No support for lossless compression.
[edit] JPEG 2000
Pros:
- Very advanced format.
- High color depth.
- Advanced lossy compression (wavelets).
- Lossless compression.
Cons:
- Not as widely supported as JPEG yet.
- Patent concerns exist.
[edit] PCX
Pros:
- Old, fairly established format.
Cons:
- Support for it is waning.
- Limited color depth.
[edit] PNG
Pros:
- Well documented, standardised format.
- Widely supported and implemented—reference implementation freely available.
- Supports very high depth images (48-bit RGB, 64-bit RGBA and 16-bit grayscale).
- One of the best-performing lossless formats.
Cons:
- No support for floating-point images.
- No support for lossy compression.
[edit] TGA
Pros:
- Incredibly simple format for uncompressed images.
- Widely supported and implemented.
Cons:
- Somewhat archaic and difficult to implement for other-than uncompressed RGB/RGBA images.
[edit] TIFF
Pros:
- Very flexible, supports a wide variety of image formats both lossy and lossless.
- Supports very high color depth.
Cons:
- Very difficult to implement.
- Has a huge number of features that might potentially need to be supported.
[edit] Vector Formats
- This article is a stub. You can help out by expanding it.
[edit] General Information
| Color space | Encoding | Embed Bitmaps? | Animation | Compression | Free | Extensible | |
|---|---|---|---|---|---|---|---|
| SVG | RGB, RGBA, HSL, CMYK | Yes | Yes | Yes | Yes | Yes | Yes |
