cjpeg 命令

常用示例

说明

cjpeg is an image compression utility from the Independent JPEG Group's (IJG) libjpeg library, also available in the optimized libjpeg-turbo variant. It compresses raster image files into JPEG/JFIF format. The utility reads input images in various formats including BMP, PPM, PGM, and Targa, then outputs compressed JPEG data. By default, output goes to standard output, allowing easy piping and redirection. Input formats are auto-detected based on file headers. For web use, the -progressive option creates images that render progressively during download. The -optimize flag reduces file size through better Huffman tables at the cost of slower encoding. Quality settings around 75-85 typically offer a good balance between file size and visual fidelity.

参数

-quality _N_

Set compression quality level (1-100). Higher values produce better quality but larger files. Default is 75.

-progressive

Create progressive JPEG file for incremental display during download.

-grayscale

Force grayscale output even if input is color.

-optimize

Optimize Huffman coding tables. Produces smaller files but slower compression.

-outfile _name_

Specify output file name instead of writing to stdout.

-targa

Input file is in Targa format (useful when auto-detection fails).

-smooth _N_

Smooth input image to reduce dithering artifacts (1-100).

-maxmemory _N_

Limit memory usage to N kilobytes.

-restart _N_

Emit restart markers every N MCU rows (or N blocks if B suffix used).

-arithmetic

Use arithmetic coding instead of Huffman coding (smaller files, less compatible).

-baseline

Force baseline JPEG output (8-bit, non-progressive).

-verbose or -debug

Enable debug output.