Imagick::sigmoidalContrastImage

Description

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. alpha indicates how much to increase the contrast: 0.00 is none; 3.00 is typical; 20.00 is pushing it. beta indicates where midtones fall in the resultant image, as a fraction of the quantum range: 0.0 is white, 0.5 is middle-gray, 1.0 is black (multiply by getQuantumRange()['quantumRangeLong'] to get the value to pass).

See also ImageMagick Examples -- Color Modifications — Sigmoidal Non-linearity Contrast.

Parameters

sharpen

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

alpha

The amount of contrast to apply. 1.00 is very little, 5.00 is a significant amount, 20.00 is extreme.

beta

Where the midpoint of the gradient will be. This value should be in the range 0.00 to 1.00 - multiplied by the quantum value for ImageMagick.

channel

Which color channels the contrast will be applied to.

Return Values

Success

Errors/Exceptions

Throws

Examples

Create a gradient image using Imagick::sigmoidalContrastImage() suitable for blending two images together smoothly, with the blending defined by alpha and beta

<?php

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

    return $imagick;
}