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Imagick: : sigmoidalContrastImage
(PECL imagick 2.0.0)
Imagick::sigmoidalContrastImage — Adjusts the contrast of an image
Description
$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.
Examples
Example #1 Create a gradient image using Imagick::sigmoidalContrastImage() suitable for blending two images together smoothly, with the blending defined by $contrast and $the midpoint
<?php
function generateBlendImage($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;
}
?>
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Document created the 30/01/2003, last modified the 26/10/2018
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