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ICC Color Profiles
Both Save for Web and Save As give you the option of including the ICC Color Profile within the image. Color profiles are used to the viewer's display how the RGB values within the image data should map to real-world colors. Assuming you have a color-managed environment (calibrated and profiled monitor), this profile is used to display the colors as they were intended to be shown.
Unfortunately, most web browsers don't read this profile and most people don't have calibrated monitors, so the default color space, sRGB is generally assumed. Therefore, if you are sharing your photos on the web, and your photos were shot in a color space such as Adobe RGB, it is strongly advised that you convert to sRGB first. Once you've done that, there is little need to include the ICC profile within the file.
Comparison of JPEG Markers
The differences between the output of the two JPEG compressed file saving methods is easily visible when comparing the JPEG (JFIF) files themselves. The JPEG (JFIF) file format specifies a number of mandatory markers as well as some optional ones. The chart below shows how Photoshop CS2 Save as and Photoshop CS2 Save for the Web compare at a low level, with the help of JPEGsnoop:
ICC顏色配置：
另存為網(wǎng)頁格式和另存為都提供了是否嵌入ICC顏色配置的選項。顏色配置是用來讓圖片文件的RGB數(shù)值在用戶顯示器上顯示出更真實的色彩。假設(shè)你有一個經(jīng)過顏色管理的環(huán)境（校準(zhǔn)和配置過的顯示器）配置能讓顏色顯示更接近預(yù)期的效果。
很不幸的是，大部分瀏覽器不支持顏色配置，并且大部分人沒有校準(zhǔn)過的顯示器，所以默認(rèn)假設(shè)是sRGB色彩空間。因此，如果你在網(wǎng)上分享照片，如果你的照片拍攝時使用的是其它色彩空間，例如Adobe RGB，那么強烈建議你轉(zhuǎn)換為sRGB。如果你這樣做的話，就基本不需要在文件中嵌入ICC顏色配置了。
通過對比jpeg文件，兩種jpeg壓縮文件保存方式的區(qū)別是很容易識別的。jpeg（jfif）文件格式中列入了一些強制的標(biāo)記和一些可選的標(biāo)記。
下面的表格是photoshop另存為和另存為網(wǎng)頁格式的輸出文件的對比。
Comparison of JPEG Markers in Photoshop
| Save As |
Save For Web |
Description |
| SOI |
SOI |
Start of Image marker |
| APP0 |
APP0 |
Identifier, Version, resolution, JFIF extensions |
| APP1 |
|
EXIF data, Makernotes removed in both. (長度 5KB) |
| APP13 |
|
Photoshop IRB (Photoshop-specific data, including quality)
|
| APP1 |
|
XML metadata (EXIF, IPTC, etc.) (長度17KB) |
| APP2* |
APP2* |
ICC color profile (* optional) (長度3KB) |
| |
APP12 |
Ducky tag - Save for Web Quality - stores the quality level
(length 17B) |
| APP14 |
APP14 |
Encoding info: color transform (e.g. YCbCr, YCCK, RGB, CMYK)
and whether or not the samples were blended (length 14B) |
| DQT |
DQT |
Quantization Tables |
| SOF0 |
SOF0 |
Baseline DCT, chroma subsampling |
| DRI |
|
Restart Intervals - Adds a level of recovery in case of errors
(length is variable, depends on frequency) |
| DHT |
DHT |
Huffman compression tables |
| SOS |
SOS |
Start of Scan: Image Data stream |
| EOI |
EOI |
End of Image marker |
As can be seen in the above table, the additional data stored within a Save As JPEG versus as Save for Web JPEG is typically in the order of ~ 40 KB. In most high-resolution photos, this extra is insignificant, but when trying to compress small images for web use, this overhead could be significant.
Photoshop兩種保存方式輸出文件的jpeg標(biāo)記對比
| 另存為 |
另存為網(wǎng)頁格式 |
說明 |
| SOI |
SOI |
圖像開始標(biāo)記 |
| APP0 |
APP0 |
識別標(biāo)記、版本、分辨率、jfif擴展 |
| APP1 |
|
EXIF數(shù)據(jù), 兩種保存方式都移除了制作者注釋(長度5KB) |
| APP13 |
|
Photoshop IRB (Photoshop特有數(shù)據(jù),包括質(zhì)量) (長度5KB) |
| APP1 |
|
XML數(shù)據(jù)(EXIF, IPTC等) (長度17KB) |
| APP2* |
APP2* |
ICC顏色配置(*可選) (長度3KB) |
| |
APP12 |
Ducky標(biāo)簽-保存為網(wǎng)絡(luò)格式質(zhì)量-儲存質(zhì)量等級(長度17B) |
| APP14 |
APP14 |
編碼信息: 顏色轉(zhuǎn)換 (例如YCbCr, YCCK, RGB, CMYK)
以及樣本是否混合(長度14B) |
| DQT |
DQT |
量化表 |
| SOF0 |
SOF0 |
基線DCT, 色度抽樣 |
| DRI |
|
重新開始間隔-加入出錯時的復(fù)原標(biāo)準(zhǔn)(長度不定) |
| DHT |
DHT |
Huffman壓縮表 |
| SOS |
SOS |
掃描開始: 圖像數(shù)據(jù)流 |
| EOI |
EOI |
圖像結(jié)束標(biāo)記 |
如上表所示，另存為輸出文件所包含的附加信息使文件比另存為網(wǎng)頁格式多40kb。對于大部分高分辨率的圖像文件來說，這部分?jǐn)?shù)據(jù)并不明顯，但如果想要壓縮圖像文件大小以供網(wǎng)頁使用，那么這部分就很明顯了。
出處：藍(lán)色理想
責(zé)任編輯：bluehearts
上一頁 PS中的"另存為"與"另存為網(wǎng)頁格式" [2] 下一頁 PS中的"另存為"與"另存為網(wǎng)頁格式" [4]
◎進入論壇Photoshop、Fireworks版塊參加討論，我還想發(fā)表評論。
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第 1 頁 
第 3 頁 PS中的"另存為"與"另存為網(wǎng)頁格式" [3]
