Nginx Module Reference Manual: Image filter Module (image filter)

If you want to use these modules, you must specify the relevant compilation parameters at compile time.

This module can make changes to a picture file (http://www.aliyun.com/zixun/aggregation/16701.html ">jpeg, GIF, and PNG") when it is passed.
To use this module, you must specify the following compilation parameters at compile time (0.7.54 version available):

This module relies on LIBGD and recommends the use of recent versions.
Sample configuration:

Instructions

Image_filter

Syntax: Image_filter (test|size|resize width height|crop width height)
Default value: None
Working with Fields: location
Specifies the type that needs to be changed. Follows：

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Image_filter_buffer

Syntax: Image_filter_buffer size
Default value: 1M
Working with fields: HTTP, server, location
Reads the maximum value of a picture.

Image_filter_jpeg_quality

Syntax: image_filter_jpeg_quality [0 ... 100]
Default value: 75
Working with fields: HTTP, server, location
Set the quality ratio of the loss when processing JPEG pictures, with a maximum recommended value of 95.

Image_filter_transparency

Syntax: Image_filter_transparency on|off
Default value: On
Working with fields: HTTP, server, location
This directive allows you to disable image transparency in GIF and palette-based PNG to improve image quality.
True Color PNG's alpha channel always exists, regardless of whether this parameter is set.
Note: Grayscale PNG is not tested and will be processed as true color.