PS文件菜單中的另存為和另存為網(wǎng)頁格式的區(qū)別

2023-11-06 17:32:09 來源/作者: / 己有:1人學(xué)習(xí)過

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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(zhǎng)度 5KB)
APP13        Photoshop IRB (Photoshop-specific data, including quality)
          (長(zhǎng)度5KB)
APP1        XML metadata (EXIF, IPTC, etc.) (長(zhǎng)度17KB)
APP2*  APP2*   ICC color profile (* optional) (長(zhǎng)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(duì)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(shí)別標(biāo)記、版本、分辨率、jfif擴(kuò)展
APP1         EXIF數(shù)據(jù), 兩種保存方式都移除了制作者注釋(長(zhǎng)度5KB)
APP13         Photoshop IRB (Photoshop特有數(shù)據(jù),包括質(zhì)量) (長(zhǎng)度5KB)
APP1         XML數(shù)據(jù)(EXIF, IPTC等) (長(zhǎng)度17KB)
APP2*  APP2*    ICC顏色配置(*可選) (長(zhǎng)度3KB)
     APP12    Ducky標(biāo)簽-保存為網(wǎng)絡(luò)格式質(zhì)量-儲(chǔ)存質(zhì)量等級(jí)(長(zhǎng)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(zhǎng)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(cuò)時(shí)的復(fù)原標(biāo)準(zhǔn)(長(zhǎng)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(duì)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。
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Extraction of Quality Setting in Save As
In files generated using Save As, you can derive the quality setting from the Photoshop IRB resource (0x0406) in the JPEG APP13 (0xFFED) marker. The following hex view is of an image saved with quality setting 2.
(圖見下)
Value       Quality
0xFFFD       Quality 1 (Low)
0xFFFE       Quality 2
0xFFFF       Quality 3
0x0000       Quality 4
0x0001       Quality 5 (Medium)
0x0002       Quality 6
0x0003       Quality 7
0x0004       Quality 8 (High)
0x0005       Quality 9
0x0006       Quality 10 (Maximum)
0x0007       Quality 11
0x0008       Quality 12

另存為的圖像質(zhì)量設(shè)置
在用另存為方式輸出的文件中,你能根據(jù)JPEG APP13 (0xFFED)標(biāo)記中的photoshop IRB資源(0x0406)數(shù)據(jù)推得圖片質(zhì)量的設(shè)置值。下面是一副保存質(zhì)量為2的圖片文件的16進(jìn)制視圖。



數(shù)值       質(zhì)量
0xFFFD       質(zhì)量1 (低)
0xFFFE       質(zhì)量2
0xFFFF       質(zhì)量3
0x0000       質(zhì)量4
0x0001       質(zhì)量5 (中)
0x0002       質(zhì)量6
0x0003       質(zhì)量7
0x0004       質(zhì)量8 (高)
0x0005       質(zhì)量9
0x0006       質(zhì)量10 (最佳)
0x0007       質(zhì)量11
0x0008       質(zhì)量12

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Extraction of Quality Setting in Save For Web
In files generated using Save For Web, you can derive the quality setting (1..100) from the Ducky resource in the JPEG APP12 (0xFFEC) marker (starts with null-terminated ASCII string Ducky). The percent value is stored in hex. The following hex view shows a file saved with quality setting 51 = 0x31:
(圖見下)

另存為網(wǎng)頁格式的質(zhì)量設(shè)置
在另存為網(wǎng)頁格式的圖片文件中,你能根據(jù)JPEG APP12 (0xFFEC)標(biāo)記(以空數(shù)據(jù)開頭、ASCII編碼Ducky結(jié)束)中的Ducky資源推得圖像質(zhì)量設(shè)置(1-100%)數(shù)據(jù)是以16進(jìn)制保存的。圖中在0x31處,16進(jìn)制數(shù)值33表示圖片質(zhì)量為51。
  


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Comparison of Save As vs Save For Web Quality
Many people are confused about why there is a difference in the definition of quality settings within Photoshop and furthermore, how they compare. The following table shows the two methods and the relative ordering of quality between the settings, from best to worst quality. See description below for the limitations of such an ordered comparison.
For more information: read about JPEG chroma subsampling.
Method   JPEG Quality Preset  Chroma Subsampling
Save For Web 100     Maximum 1x1
Save As    12     Maximum  1x1
Save For Web 90           1x1
Save As    11           1x1
Save For Web 80     Very High 1x1
Save As    10           1x1
Save For Web 70           1x1
Save As    9            1x1
Save For Web 60      High   1x1
Save As    8      High   1x1
Save For Web 51           1x1
Save For Web 50           2x2
Save As    6            2x2
Save As    7            1x1
Save As    5      Medium  2x2
Save For Web 40           2x2
Save As    4            2x2
Save As    3      Low    2x2
Save For Web 30     Medium  2x2
Save As    2            2x2
Save For Web 20           2x2
Save As    1           2x2
Save For Web 10     Low    2x2

In graphical form, here is a chart that shows a comparison of the JPEG luminance and chrominance across the default presets, each with the equivalent JPEG standard "quality factor". Of course, it is important to note that the quality factor shown is not an accurate measure of image quality since they are only truly comparable quantities if both Save for Web and Save As were based on linear scalings of the quantization tables included in the JPEG Standard Annex. Since neither is based on the sample tables, the quality factor should only be taken as a very rough comparison measure. The graph is ordered by decreasing luminance quality factors.
(圖見下)
Ordered Graph
(圖見下)
Comparison Graph

另存為和另存為網(wǎng)頁格式的比較
很多人對(duì)為何photoshop中的兩種保存方式質(zhì)量設(shè)定的定義有區(qū)別而不解,還有怎么比較他們。下面的表格是兩種保存方法設(shè)置質(zhì)量后的圖像質(zhì)量排序,從最佳質(zhì)量到最低質(zhì)量。這種排序比較的局限性請(qǐng)看后面的說明。
更多信息請(qǐng)查閱jpeg色度抽樣。
保存方法    JPEG質(zhì)量  預(yù)設(shè)   色度抽樣
另存為網(wǎng)頁格式 100    最佳    1x1
另存為     12     最佳         1x1
另存為網(wǎng)頁格式 90           1x1
另存為     11           1x1
另存為網(wǎng)頁格式 80     較高    1x1
另存為     10           1x1
另存為網(wǎng)頁格式 70           1x1
另存為     9            1x1
另存為網(wǎng)頁格式 60     高     1x1
另存為     8      高     1x1
另存為網(wǎng)頁格式 51           1x1
另存為網(wǎng)頁格式 50           2x2
另存為     6            2x2
另存為     7            1x1
另存為     5      中     2x2
另存為網(wǎng)頁格式 40           2x2
另存為     4            2x2
另存為     3      低     2x2
另存為網(wǎng)頁格式 30      中    2x2
另存為     2            2x2
另存為網(wǎng)頁格式 20           2x2
另存為    1             2x2
另存為網(wǎng)頁格式 10      低     2x2

下面是默認(rèn)設(shè)置下的jpeg亮度和色度的對(duì)比圖表,每個(gè)都有對(duì)應(yīng)的jpeg標(biāo)準(zhǔn)質(zhì)量系數(shù)。當(dāng)然,有必要指出,質(zhì)量系數(shù)不是測(cè)量圖片質(zhì)量的精確標(biāo)準(zhǔn),只是如果另存為網(wǎng)頁格式和另存為都是基于jpeg標(biāo)準(zhǔn)附錄中的量化表的線性測(cè)量,那么質(zhì)量系數(shù)是唯一能用來比較圖片質(zhì)量的參數(shù)。質(zhì)量系數(shù)只能作為一個(gè)粗糙的標(biāo)準(zhǔn)來比較圖片。圖表按亮度質(zhì)量系數(shù)降序排列。
  

排序圖表
  

對(duì)比圖表

標(biāo)簽(TAG) 新手教程 保存技巧