# PHP的图片处理功能

- URL: https://wuming.si/blog/563/
- Author: Aaron
- Published: 2014-06-22
- Language: en
- Categories: Technology
- Originally published at: https://blog.wo.ai/archives/563

在一个小项目里需要用到php的图像处理功能，才发现php通过imagefilter能够实现强大的功能。

# imagefilter

(PHP 5)

imagefilter — Applies a filter to an image

### Description

bool imagefilter ( resource `$image` , int `$filtertype` [, int `$arg1` [, int `$arg2` [, int `$arg3`[, int `$arg4` ]]]] )

imagefilter() applies the given filter `filtertype` on the `image`.

### Parameters

`image`
    An image resource, returned by one of the image creation functions, such as [imagecreatetruecolor()](http://www.php.net/manual/en/function.imagecreatetruecolor.php).
`filtertype`
    `filtertype` can be one of the following: 

  * `IMG_FILTER_NEGATE`: Reverses all colors of the image.
  * `IMG_FILTER_GRAYSCALE`: Converts the image into grayscale.
  * `IMG_FILTER_BRIGHTNESS`: Changes the brightness of the image. Use `arg1` to set the level of brightness.
  * `IMG_FILTER_CONTRAST`: Changes the contrast of the image. Use `arg1` to set the level of contrast.
  * `IMG_FILTER_COLORIZE`: Like `IMG_FILTER_GRAYSCALE`, except you can specify the color. Use `arg1`, `arg2` and`arg3` in the form of `red`, `green`, `blue` and `arg4` for the `alpha` channel. The range for each color is 0 to 255.
  * `IMG_FILTER_EDGEDETECT`: Uses edge detection to highlight the edges in the image.
  * `IMG_FILTER_EMBOSS`: Embosses the image.
  * `IMG_FILTER_GAUSSIAN_BLUR`: Blurs the image using the Gaussian method.
  * `IMG_FILTER_SELECTIVE_BLUR`: Blurs the image.
  * `IMG_FILTER_MEAN_REMOVAL`: Uses mean removal to achieve a “sketchy” effect.
  * `IMG_FILTER_SMOOTH`: Makes the image smoother. Use `arg1` to set the level of smoothness.
  * `IMG_FILTER_PIXELATE`: Applies pixelation effect to the image, use `arg1` to set the block size and `arg2` to set the pixelation effect mode.

`arg1`
    

  * `IMG_FILTER_BRIGHTNESS`: Brightness level.
  * `IMG_FILTER_CONTRAST`: Contrast level.
  * `IMG_FILTER_COLORIZE`: Value of red component.
  * `IMG_FILTER_SMOOTH`: Smoothness level.
  * `IMG_FILTER_PIXELATE`: Block size in pixels.

`arg2`
    

  * `IMG_FILTER_COLORIZE`: Value of green component.
  * `IMG_FILTER_PIXELATE`: Whether to use advanced pixelation effect or not (defaults to `FALSE`).

`arg3`
    

  * `IMG_FILTER_COLORIZE`: Value of blue component.

`arg4`
    

  * `IMG_FILTER_COLORIZE`: Alpha channel, A value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.

### Return Values

Returns `TRUE` on success or `FALSE` on failure.

我用到的几个功能

imagefilter($dst_r, IMG_FILTER_BRIGHTNESS, -80);

The documentation misses the exact meaning and valid ranges of the arguments for ImageFilter(). According to the 5.2.0 sources the arguments are:  
IMG_FILTER_BRIGHTNESS  
-255 = min brightness, 0 = no change, +255 = max brightness

IMG_FILTER_CONTRAST  
-100 = max contrast, 0 = no change, +100 = min contrast (note the direction!)

IMG_FILTER_COLORIZE  
Adds (subtracts) specified RGB values to each pixel. The valid range for each color is -255…+255, not 0…255. The correct order is red, green, blue.  
-255 = min, 0 = no change, +255 = max  
This has not much to do with IMG_FILTER_GRAYSCALE.

IMG_FILTER_SMOOTH  
Applies a 9-cell convolution matrix where center pixel has the weight arg1 and others weight of 1.0. The result is normalized by dividing the sum with arg1 + 8.0 (sum of the matrix).  
any float is accepted, large value (in practice: 2048 or more) = no change

ImageFilter seem to return false if the argument(s) are out of range for the chosen filter.

You must add `imagesavealpha($im, true);` so the alpha channel will be saved on the new image.
    
    
    $im = imagecreatefrompng('image.png');
    imagealphablending($im, false);
    
    imagesavealpha($im, true);
    
    if($im && imagefilter($im, IMG_FILTER_COLORIZE, 0,0,255,0)) {
        imagepng($im, 'image-new.png');
        imagedestroy($im);
    }