imageconvolution()

(PHP 5 >= 5.1.0, PHP 7)

用系数 div 和 offset 申请一个 3x3 的卷积矩阵

说明

Applies a convolution matrix on the image, using the given coefficient and offset.

参数

由图象创建函数(例如imagecreatetruecolor())返回的图象资源。

A 3x3 matrix: an array of three arrays of three floats.

The divisor of the result of the convolution, used for normalization.

Color offset.

返回值

成功时返回TRUE，或者在失败时返回FALSE。

范例

Embossing the PHP.net logo

以上例程会输出：

Gaussian blur

以上例程会输出：

注释

Note:此函数仅在与 GD 库捆绑编译的 PHP 版本中可用。

参见

• imagefilter()对图像使用过滤器

Here's a good sharpen setting for thumbnail creation: 

Matrices can be used for sharpening, blurring, edge detection, etc, ala Photoshop.
A sharpening example:

Below is some information on building different kinds of matrices. (If you have photoshop (or PSP, GIMP) you can test out your matrices before applying them in PHP)
http://loriweb.pair.com/8udf-basics.html (covers blurs)
http://loriweb.pair.com/8udf-sharpen.html
http://loriweb.pair.com/8udf-edges.html
http://loriweb.pair.com/8udf-emboss.html

Normalization is necessary to keep the image balanced (else any filter may quickly turn the image almost completely black or white).
Here is a short, easy-to-use, class to handle normalization automatically and make for easier input of the 3x3 matrix:
The code respects the "array of three arrays" syntax for use with the imageconvolution() function and automatically calculates the necesarry divisor for normalization.

Example usage:

Some common filters:

Remember you can use imagefilter() for such basic needs but the above class will make it easier for you when you want to create your own filters.

imageconvolution() does not appear in PHP with non-bundled GD libraries. It is a rare situation, but it still happens. That's why I wrote a replication of imageconvolution() in PHP. Compare to the post below, this one makes the use of offset and 30% faster.
Because it's written in PHP, it is 50 times slower than the bundled version.
Actually, this is a replication of gdimageconvolutaion() of GD library, it does not support data validating feature imageconvolution() have. But I guess people who uses this function knows their stuff.
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