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颜色配置：

另存为网页格式和另存为都提供了是否嵌入ICC颜色配置的选项。颜色配置是用来让图片文件的RGB数值在用户显示器上显示出更真实的色彩。假设你有一个经过颜色管理的环境（校准和配置过的显示器）配置能让颜色显示更接近预期的效果。
很不幸的是，大部分浏览器不支持颜色配置，并且大部分人没有校准过的显示器，所以默认假设是sRGB色彩空间。因此，如果你在网上分享照片，如果你的照片拍摄时使用的是其它色彩空间，例如Adobe RGB，那么强烈建议你转换为sRGB。如果你这样做的话，就基本不需要在文件中嵌入ICC颜色配置了。
通过对比jpeg文件，两种jpeg压缩文件保存方式的区别是很容易识别的。jpeg（jfif）文件格式中列入了一些强制的标记和一些可选的标记。

下面的表格是photoshop另存为和另存为网页格式的输出文件的对比。

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. (长度 5KB)
APP13		Photoshop IRB (Photoshop-specific data, including quality)
APP1		XML metadata (EXIF, IPTC, etc.) (长度17KB)
APP2*	APP2*	ICC color profile (* optional) (长度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两种保存方式输出文件的jpeg标记对比

另存为	另存为网页格式	说明
SOI	SOI	图像开始标记
APP0	APP0	识别标记、版本、分辨率、jfif扩展
APP1		EXIF数据, 两种保存方式都移除了制作者注释(长度5KB)
APP13		Photoshop IRB (Photoshop特有数据,包括质量) (长度5KB)
APP1		XML数据(EXIF, IPTC等) (长度17KB)
APP2*	APP2*	ICC颜色配置(*可选) (长度3KB)
	APP12	Ducky标签-保存为网络格式质量-储存质量等级(长度17B)
APP14	APP14	编码信息: 颜色转换 (例如YCbCr, YCCK, RGB, CMYK) 以及样本是否混合(长度14B)
DQT	DQT	量化表
SOF0	SOF0	基线DCT, 色度抽样
DRI		重新开始间隔-加入出错时的复原标准(长度不定)
DHT	DHT	Huffman压缩表
SOS	SOS	扫描开始: 图像数据流
EOI	EOI	图像结束标记

如上表所示，另存为输出文件所包含的附加信息使文件比另存为网页格式多40kb。对于大部分高分辨率的图像文件来说，这部分数据并不明显，但如果想要压缩图像文件大小以供网页使用，那么这部分就很明显了。

出处：蓝色理想
责任编辑：bluehearts

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