Adjusts the contrast of an image

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- Adjusts the contrast of an image

# Imagick::sigmoidalContrastImage

(PECL imagick 2, PECL imagick 3)

Imagick::sigmoidalContrastImage — Adjusts the contrast of an image

### Description

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

### 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.

### Return Values

Returns `true` on success.

### Errors/Exceptions

Throws ImagickException on error.

### Examples

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

    <?phpfunction 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; }?>