image

Command-line image manipulation tools

Usage

JRE 16 is required, older versions are not supported. That fact alone should be enough for you not to consider actually using this thing. And yes, I do use some newer language features.

java -jar image.jar [--input input_image] [--output output_image] [options]

Download a pre-compiled jar file from Releases or use the maven package command.

I may eventually try using jpackage to compile regular executables, but for now you'll have to do it this way.

Options:

• -i, --input <path>

• -o, --output <path>

• -b, --brighten <amount>

  • Values range from 0 (no change) to 255 (clip everything white)

• -d, --darken <amount>

  • Values range from 0 (no change) to 255 (clip everything black)

• -f, --filter <filter>

  • See Filters section below

• -l, --list-filters

• -p, --palette <path|text>

• -r, --resize <WxH>

• -rq, --resize-quick <WxH>

  • About 5x quicker than regular resize, though quality takes a hit for natural images

• --iterations <num>

  • Higher amount approximates a Gaussian blur when using the box-blur filter

• --radius <pixels>

• -h, --help

  • Help also shows when program is run without any arguments

• -V, --version

Examples

Resize an image to full HD:

java -jar image.jar --input input.png --output output.png --resize 1920x1080

Blur an image using default settings:

java -jar image.jar --input input.png --output output.png --filter box_blur

Resize, brighten, blurring, dithering and grayscale an image (why would you do this?), all with custom settings and enabling debug messages:

java -jar image.jar \
--input input.png \
--output output.png \
--resize 1366x768 \
--brighten 20 \
--filter box_blur \
--radius 20 \
--iterations 2 \
--filter floyd_steinberg \
--palette palette.txt \
--filter grayscale \ 
--debug

Filters

• Grayscale conversion

  • grayscale, grayscale_average, grayscale_min, grayscale_max, grayscale_perceptual

• Palette conversion, dithering

  • floyd_steinberg, nearest_color

• Blurring

  • box_blur

• Resizing

  • resize, resize_fast

• Brightness correction

  • brighten, darken

Filter parameters

• Grayscale filters require no additional configuration.

• Palette conversion filters require a target palette; see Using and formatting palettes section below.

  • --palette <text|path>

• Blur filters can take user-defined radius and iteration values, or fall back to standard values (radius=5, iterations=1).

  • --radius <pixels>
  • --iterations <num>

• Resize filters require either a target size in the form of WIDTHxHEIGHT or only the size of the longest side (calculates the smaller side to preserve the aspect ratio)

  • e.g. --resize 1920x1080 or --resize 1920

Using and formatting palettes

In order to use palette conversion filters, this program requires a target palette.

You can either define palettes by writing them out as a command-line argument using the --palette flag, or using a text file instead. Colours must be in hexadecimal form: #RRGGBB.

Supported formatting as a command-line argument:

--palette "#FFFFFF #63D0E4 #000000"

A text file should use newlines instead of whitespaces:

#FFFFFF
#63D0E4
#000000

Use the text file by pointing the --palette flag to it.

--palette path-to-file.txt