Image Filter

The module is a filter that transforms images in JPEG, GIF, PNG, and WebP formats.

When building from the source code, this module isn’t built by default; it should be enabled with the ‑‑with‑http_image_filter_module build option.

In our repositories, the module is built dynamically and is available as a separate package named angie-module-image-filter.

Important

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

To transform images in WebP format, the libgd library must be compiled with the WebP support.

Configuration Example

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

location = /empty {
    empty_gif;
}

Directives

image_filter

Syntax	image_filter off; image_filter test; image_filter size; image_filter rotate 90 | 180 | 270; image_filter resize width height; image_filter crop width height;
Default	image_filter off;
Context	location

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.

image_filter_buffer

Syntax	image_filter_buffer size;
Default	image_filter_buffer 1M;
Context	http, server, location

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

image_filter_interlace

Syntax	image_filter_interlace on | off;
Default	image_filter_interlace off;
Context	http, server, location

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

image_filter_jpeg_quality

Syntax	image_filter_jpeg_quality quality;
Default	image_filter_jpeg_quality 75;
Context	http, server, location

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.

image_filter_sharpen

Syntax	image_filter_sharpen percent;
Default	image_filter_sharpen 0;
Context	http, server, location

Increases sharpness of the final image. The sharpness percentage can exceed 100. The 0 value disables sharpening. Parameter value can contain variables.

image_filter_transparency

Syntax	image_filter_transparency on | off;
Default	image_filter_transparency on;
Context	http, server, location

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.

image_filter_webp_quality

Syntax	image_filter_webp_quality quality;
Default	image_filter_webp_quality 80;
Context	http, server, location

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.