Imagick::sigmoidalContrastImage

(PECL imagick 2, PECL imagick 3)

Imagick::sigmoidalContrastImageAdjusts the contrast of an image

说明

public Imagick::sigmoidalContrastImage(
    bool $sharpen,
    float $alpha,
    float $beta,
    int $channel = Imagick::CHANNEL_DEFAULT
): bool

Adjusts the contrast of an image with a non-linear sigmoidal contrast algorithm. Increase the contrast of the image using a sigmoidal transfer function without saturating highlights or shadows. Contrast indicates how much to increase the contrast (0 is none; 3 is typical; 20 is pushing it); mid-point indicates where midtones fall in the resultant image (0 is white; 50 is middle-gray; 100 is black). Set sharpen to true to increase the image contrast otherwise the contrast is reduced.

See also » ImageMagick v6 Examples - Image Transformations — Sigmoidal Non-linearity Contrast

参数

sharpen

If true increase the contrast, if false decrease the contrast.

alpha

The amount of contrast to apply. 1 is very little, 5 is a significant amount, 20 is extreme.

beta

Where the midpoint of the gradient will be. This value should be in the range 0 to 1 - mutliplied by the quantum value for ImageMagick.

channel

Which color channels the contrast will be applied to.

返回值

成功时返回 true

错误/异常

错误时抛出 ImagickException。

示例

示例 #1 Create a gradient image using Imagick::sigmoidalContrastImage() suitable for blending two images together smoothly, with the blending defined by $contrast and $the midpoint

<?php

function generateBlendImage($width, $height, $contrast = 10, $midpoint = 0.5) {
$imagick = new Imagick();
$imagick->newPseudoImage($width, $height, 'gradient:black-white');
$quanta = $imagick->getQuantumRange();
$imagick->sigmoidalContrastImage(true, $contrast, $midpoint * $quanta["quantumRangeLong"]);

return
$imagick;
}

?>