JPEG XR
 | 模板參量錯誤！（代碼36）
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| 副檔名 |
.wdp/.hdp |
|---|---|
| 網路媒體型式 |
image/vnd.ms-photo |
| 開發者 | Microsoft |
| 格式類型 | 圖形文件格式 |
HD Photo (舊稱Windows Media Photo)是一種連續色調靜止圖像壓縮算法和文件格式，由Microsoft開發，屬於Windows Media家族的一部分。它支持有損數據壓縮以及無損數據壓縮，並且是微軟的XPS文檔的首選圖像格式。它以前在內部被稱為photon。目前其軟件支持並不廣泛，但是.NET Framework 3.0已經提供了它的官方編碼解碼器。
描述
HD Photo 是一款可以實現高動態範圍圖像編碼，而且在壓縮與解壓時只需要整數運算的圖像編解碼器。它支持單色、RGB、CMYK、甚至支持 16 位無符號整數或者 32 位定點或者浮點數表示的多通道彩色，並且它還支持 RGBE Radiance。它可以選擇嵌入 ICC 彩色 profile 以實現不同設備上的色彩一致性。阿爾法通道可以表示透明，同時支持 EXIF、XMP 元數據格式。這種格式還支持在一個文件中包含多幅圖像。支持只對圖像的進行部分解碼，對於一些特定的操作如裁剪、downsampling、水平豎直翻轉或者 cardinal 旋轉都無需對整幅圖像進行解碼。
所有的顏色表示都轉換成一種內部的色彩表示，這個變換過程是完全可逆的，因此使用合適的不同量化器可以實現有損或者無損數據壓縮。
壓縮算法
HD Photo uses a reversible color space conversion, a reversible lapped biorthogonal transform and a non-arithmetic entropy encoding scheme, which is very efficient in preserving high frequency image data. This makes the algorithm retain a higher image quality at high compression ratios. The transform operation needs 3 multiply and add operations and 7 add or shift operations at the highest quality level and in the highest performance mode, 1 multiply and add operation and 4 add or shifts are required per pixel, giving the codec a high performance. HD Photo processes images in 16x16 macroblocks.
HD Photo supports various color formats and multiple fixed and floating point numerical representation, thus giving a wide range of compression options. To remain compatible across various devices, it differentiates Basic and Advanced formats. While digital photography needs are satisfied by the Basic format, 3D rendering or advanced image processing scenarios require the Advanced format.
Microsoft claims that HD Photo offers a "perceptible image quality comparable to JPEG 2000 with computational and memory performance more closely comparable to JPEG and delivers a lossy compressed image of better perceptive quality than JPEG at less than half the file size, and that the lossless compression compresses images 2.5 times".
容器格式
HD Photo uses a TIFF-like file container to store image data in a table of Image File Directory (IFD) tags. An HD Photo file contains image data, an optional alpha channel data, HD Photo metadata, optional XMP metadata stored as XML, and optional EXIF metadata, in IFD tags. The image data is a contiguous self-contained chunk of data. The optional alpha channel, if present, is compressed as a separate image record, enabling decoding of the image data independently of transparency data in applications which do not support transparency.
Being TIFF-based, this format inherits all of the inadequacies of the TIFF format including the 4GB file-size limit, which according to the HD Photo specification[1] "will be addressed in a future update".
許可
微軟公司擁有 HD Photo 技術的專利，微軟公司向外界提供一個附帶授權協議的「HD Photo Device Porting Kit 1.0」以鼓勵人們使用這種產品。但是，這個協議的條款特別註明禁止將其用於任何開放源代碼的系統。[2]
| “ | 2. c. Distribution Restrictions. You may not ... modify or distribute the source code of any Distributable Code so that any part of it becomes subject to an Excluded License. An Excluded License is one that requires, as a condition of use, modification or distribution, that the code be disclosed or distributed in source code form; or others have the right to modify it. | ” |
引用
- ^ Windows Media Photo Specification. [2006-06-29].
- ^ HD Photo Device Porting Kit 1.0. Microsoft, Inc. 12/21/2006.
參見
外部連結
- HD Photo Specification （僅僅定義了 container 的格式與 API，沒有定義圖像格式規範）
- Windows Media Photo comparison with modern JPEG-2000 implementations (9 JPEG-2000 codecs was compared with WMP)
- Microsoft shows off JPEG rival, CNET News, 24 May 2006
- Vista to give HD Photo format more exposure, CNET News, 26 January 2007
- Bill Crow's Windows Media Photo Blog 解釋使用許可、技術細節以及提供了編解碼器的下載。