Module ngx_http_image_filter_module

• Example Configuration
• Directives
• image_filter
• image_filter_buffer
• image_filter_interlace
• image_filter_jpeg_quality
• image_filter_sharpen
• image_filter_transparency
• image_filter_webp_quality

The ngx_http_image_filter_module module (0.7.54+) is a filter that transforms images in JPEG, GIF, PNG, and WebP formats.

This module is not built by default, it should be enabled with the --with-http_image_filter_module configuration parameter.

This module utilizes the libgd library. It is recommended to use the latest available version of the library.

The WebP format support appeared in version 1.11.6. To transform images in this format, the libgd library must be compiled with the WebP support.

Example Configuration

location /img/ {
    proxy_pass   http://backend;
    image_filter resize 150 100;
    image_filter rotate 90;
    error_page   415 = /empty;
}

location = /empty {
    empty_gif;
}

Directives

Sets the type of transformation to perform on images:

off

turns off module processing in a surrounding location.

test

ensures that responses are images in either JPEG, GIF, PNG, or WebP format. Otherwise, the 415 (Unsupported Media Type) error is returned.

size

outputs information about images in a JSON format, e.g.:

{ "img" : { "width": 100, "height": 100, "type": "gif" } }

In case of an error, the output is as follows:

{}

rotate 90|180|270

rotates images counter-clockwise by the specified number of degrees. Parameter value can contain variables. This mode can be used either alone or along with the resize and crop transformations.

resize width height

proportionally reduces an image to the specified sizes. To reduce by only one dimension, another dimension can be specified as “-”. In case of an error, the server will return code 415 (Unsupported Media Type). Parameter values can contain variables. When used along with the rotate parameter, the rotation happens after reduction.

crop width height

proportionally reduces an image to the larger side size and crops extraneous edges by another side. To reduce by only one dimension, another dimension can be specified as “-”. In case of an error, the server will return code 415 (Unsupported Media Type). Parameter values can contain variables. When used along with the rotate parameter, the rotation happens before reduction.

Sets the maximum size of the buffer used for reading images. When the size is exceeded the server returns error 415 (Unsupported Media Type).

If enabled, final images will be interlaced. For JPEG, final images will be in “progressive JPEG” format.

Sets the desired quality of the transformed JPEG images. Acceptable values are in the range from 1 to 100. Lesser values usually imply both lower image quality and less data to transfer. The maximum recommended value is 95. Parameter value can contain variables.

Increases sharpness of the final image. The sharpness percentage can exceed 100. The zero value disables sharpening. Parameter value can contain variables.

Defines whether transparency should be preserved when transforming GIF images or PNG images with colors specified by a palette. The loss of transparency results in images of a better quality. The alpha channel transparency in PNG is always preserved.

Sets the desired quality of the transformed WebP images. Acceptable values are in the range from 1 to 100. Lesser values usually imply both lower image quality and less data to transfer. Parameter value can contain variables.