Enhances the contrast of a color image

# Imagick::contrastStretchImage

(PECL imagick 2, PECL imagick 3)

Imagick::contrastStretchImage — Enhances the contrast of a color image

### 说明

public function Imagick::contrastStretchImage(float `$black_point`, float `$white_point`, int `$channel` = Imagick::CHANNEL_DEFAULT): bool

Enhances the contrast of a color image by adjusting the pixels color to span the entire range of colors available. 此方法在Imagick基于ImageMagick 6.2.9以上版本编译时可用。

### 参数

`black_point`

  The black point.

`white_point`

  The white point.

`channel`

  Provide any channel constant that is valid for your channel mode. To apply to more than one channel, combine channeltype constants using bitwise operators. `Imagick::CHANNEL_ALL`. Refer to this list of channel constants.

### 返回值

成功时返回 `true`。

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