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Joint Photographic Experts Group (JPG)

Today it is the most widely spread format for image storage and web publishing. Settings of this format are adjusted with the help of the following parameters:

• bpp - color depth (default - 24 bpp)
• bpp_lossl - bits per pixel for lossless mode
• bpp_exseq - bits per pixel for extended sequential mode
• quality - image quality (default - 85%)
• mode - compression mode (default - baseline)
• sample - compression sample (default - 1:1:1 [:1])
• thumbnail - create thumbnail (default - no)
• exif - save EXIF (default - no)
• iptc - save IPTC (default - no)

bpp

Bpp parameter specifies the number of bits used to transfer the color of one pixel. Its allowed values are:

• 8 - 8 bpp (Grayscale)
• 24 - 24 bpp (True color, YCbCr/RGB for Lossless)
• 32 - 32 bpp (True color, YCCK)

The default value is: 24.

bpp_lossl

bpp_lossl parameter specifies the number of bits per pixel for lossless mode. Its allowed values are:

• 64 - 64 bpp
• 32 - 32 bpp
• 48 - 48 bpp
• 36 - 36 bpp
• 24 - 24 bpp
• 16 - 16 bpp
• 12 - 12 bpp
• 8 - 8 bpp

bpp_exseq

bpp_exseq parameter specifies the number of bits per pixel for extended sequential mode. Its allowed values are:

• 48 - 48 bpp
• 32 - 32 bpp
• 36 - 36 bpp
• 24 - 24 bpp
• 32CMYK - 32 bpp (True color, YCCK)
• 36RGB - 36 bpp (True color, RGB)
• 24RGB - 24 bpp (True color, RGB)
• 12 - 12 bpp
• 8 - 8 bpp

quality

Quality parameter specifies image quality. The higher is its value, the better is image quality. Its allowed values are whole numbers from 25 to 100. The default value is: 85.

mode

Mode parameter specifies the compression algorithm used to create resulting files. Its allowed values are:

• baseline - grayscale, YCbCr, RGB, YCbCrK, CMYK - it is the most widely spread modification of JPEG. Most images in the world are now stored as Baseline YCbCr JPEG.
• progressive - used mostly in Internet to quickly display images "on the fly". Usually, a small part of transferred data is enough to display a rough version of the image.
• lossless - this JPEG modification is often used in medical images. 12 и 16 bit grayscale JPEG is one of standard output formats for various types of medical equipment.
• sequential

The default value is: baseline.

sample

Sample parameter specifies channels of image compression. Today most JPEG files have YcbCr format (where Y-channel stands for brightness while Cb and Cr channels stand for color). Human eye is built in such a way that it perceives brightness change of neighboring pixels first and color change next. If we write an average true color image of photo quality into JPEG format, we can skip every second horizontal value of color channels and still have an image of nearly same quality. Each two pixels of the saved image will have two values of Y channel and one value of Cb and Cr channels. In Image Converter Command Line, this write mode is specified with “sample 4:2:2” parameter. Sample parameter can accept the following values:

• 111 - 1:1:1 - YY CbCb CrCr, YY CbCb CrCr
• 422 - 4:2:2 - YY CbCb CrCr, YY .... ....
• 421 - 4:2:1 - YY CbCb Cr.., YY .... ....
• 422 - 4:2:2 - YY CbCb CrCr, YY CbCb ....
• 411 - 4:1:1 - YY Cb.. Cr.., YY .... ....

The default value is: 111.

thumbnail

Thumbnail parameter specifies whether image thumbnails should be created. Thumbnails are used to quickly preview images in browsers and graphics viewers. Its allowed values are:

• Yes - create thumbnails.
• No - do not create thumbnails.

The default value is: No.

exif

Exif parameter specifies whether EXIF (information on shooting parameters of the camera used) will be saved in resulting files. Its allowed values are:

• Yes - save EXIF in resulting files.
• No - do not save EXIF in resulting files.

The default value is: No

iptc

Iptc parameter specifies whether IPTC (metadata - name, copyright, category) will be saved in resulting files. Its allowed values are:

• Yes - save IPTC in resulting files.
• No - do not save IPTC in resulting files.

The default value is: No.