Imagick::sigmoidalContrastImage

Adjusts the contrast of an image

&reftitle.description; public `bool` `Imagick::sigmoidalContrastImage` `bool` `sharpen` `float` `alpha` `float` `beta` `int` `channel` Imagick::CHANNEL_DEFAULT

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

&reftitle.parameters;

`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.

&reftitle.returnvalues;

&imagick.return.success;

&reftitle.errors;

&imagick.imagick.throws;

&reftitle.examples;

### 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;
    }

    ?>