Imagick - soft polygon edges with image mask - php

Question

How can I draw image with smooth edges using setImageClipMask?
My code produces like this:
which has sharp jagged edges where the edge of the clip mask is.
The code I am using:
// Draw clip mask
$clipMask = new \Imagick();
$clipMask->newPseudoImage($width, $height, "canvas:white");
$draw = new \ImagickDraw();
$draw->setFillColor(new ImagickPixel('black'));
$draw->polygon($myCoordinates);
$clipMask->drawImage($draw);
// Set mask
$img_main->setImageClipMask($clipMask);
// Draw image
$img_main->compositeImage($myImage, Imagick::COMPOSITE_DEFAULT, $x, $y);

Answer 1

tl:dr don't use masks use a gradient instead.
Masks are a binary choice; the pixel either gets through or it doesn't and are designed to have sharp edges.
Gradients (which don't have to be linear) allow for effects to be applied smoothly. The code below generates a gradient and then uses it to blend between the two images smoothly.
Gradient generated:
Output image:
<?php
$background = new \Imagick(realpath('./Skyline_400.jpg'));
$overlay = new \Imagick(realpath('./background.jpg'));
$overlay->scaleimage(
$background->getImageWidth(),
$background->getImageHeight()
);
$gradient = createGradient($background);
//If you need to see the gradient for debugging.
$gradient->setImageFormat("png");
$gradient->writeImage("./gradient.png");
$gradient2 = clone $gradient;
//The overlay needs to have the gradient reversed
$gradient2->negateimage(false);
$gradient2->setImageAlphaChannel(\Imagick::ALPHACHANNEL_DEACTIVATE);
$background->compositeImage($gradient2, \Imagick::COMPOSITE_COPYOPACITY, 0, 0);
$gradient->setImageAlphaChannel(\Imagick::ALPHACHANNEL_DEACTIVATE);
$overlay->compositeimage($gradient, \Imagick::COMPOSITE_COPYOPACITY, 0, 0);
//Create a new canvas to render everything in to.
$canvas = new \Imagick();
$canvas->newImage($gradient->getImageWidth(), $gradient->getImageHeight(), new \ImagickPixel('black'));
//Blend background into canvas
$canvas->compositeimage($background, \Imagick::COMPOSITE_BLEND, 0, 0);
//Blend overlay into canvas
$canvas->compositeimage($overlay, \Imagick::COMPOSITE_BLEND, 0, 0);
//Output the final image
$canvas->setImageFormat('png');
$canvas->writeImage("./output_test.png");
// Create a gradient/mask to allow images to be blended smoothly.
function createGradient(\Imagick $background)
{
$myCoordinates = [
['x' => 20, 'y' => 20,],
['x' => 360, 'y' => 20,],
['x' => 350, 'y' => 350,],
['x' => 25, 'y' => 350,],
];
$backgroundMask = new \Imagick();
$backgroundMask->newPseudoImage(
$background->getImageWidth(),
$background->getImageHeight(),
'canvas:white'
);
$draw = new \ImagickDraw();
$draw->setFillColor(new ImagickPixel('black'));
$draw->polygon($myCoordinates);
$backgroundMask->setImageFormat('png');
$backgroundMask->drawImage($draw);
// Blur the edges to make the transition between black and white
// be smooth
$backgroundMask->blurImage(2, 0.5);
return $backgroundMask;
}