imagecopyresampled with opacity

Question

I want to add a small image on anther big image as a watermark with opacity.

I'm using imagecopyresampled to put image on anther image.

But, how to provide opacity for watermark image.

Please help me.

I'm using this simple example code for add watermark on image without opacity:

<?php

$background = imagecreatefrompng("background.png");

if ($background !== false) {
    $watermark = imagecreatefrompng("watermark.png");
    // Add watermark on background
    imagecopyresampled($background,$watermark,
        100, 100, 0, 0,
        128, 128, 128, 128);
    // Add image header
    header("Content-type: image/png");
    imagepng($background);
    imagedestroy($background);
}

For example:

This is background or main image

This is background or main image

This is watermark image

enter image description here

I want this type of output

enter image description here

Is it possible or not in PHP?

Nice images and examples but can we see your code which didn't work? — Hanky Panky, Aug 23 '14 at 06:20
@Hanky웃Panky Now, I'm updated my question with example PHP code. — Temüjin, Aug 23 '14 at 06:30
http://stackoverflow.com/questions/32243/can-png-image-transparency-be-preserved-when-using-phps-gdlib-imagecopyresample — Hanky Panky, Aug 23 '14 at 06:32
Hi I'm already read this question. It's not suitable for my problem. I want to add image as water mark with opacity. — Temüjin, Aug 23 '14 at 06:34
Not an expert of how PHP handles images, but I would process manually the image, processing all the pixel by doing an average of the colours of the background and the foreground image. Of course you would also need to calculate the correct offsets (positioning) of the image. — fstab, Aug 23 '14 at 10:00

score 3 · Answer 1 · answered Sep 15 '14 at 10:32

Just use this simple PHP function:

<?php

function filter_opacity(&$img, $opacity) //params: image resource id, opacity in percentage (eg. 80)
{
    if (!isset($opacity)) {
        return false;
    }
    $opacity /= 100;

    //get image width and height
    $w = imagesx($img);
    $h = imagesy($img);

    //turn alpha blending off
    imagealphablending($img, false);

    //find the most opaque pixel in the image (the one with the smallest alpha value)
    $minalpha = 127;
    for ($x = 0; $x < $w; $x++) {
        for ($y = 0; $y < $h; $y++) {
            $alpha = (imagecolorat($img, $x, $y) >> 24) & 0xFF;
            if ($alpha < $minalpha) {
                $minalpha = $alpha;
            }
        }
    }

    //loop through image pixels and modify alpha for each
    for ($x = 0; $x < $w; $x++) {
        for ($y = 0; $y < $h; $y++) {
            //get current alpha value (represents the TANSPARENCY!)
            $colorxy = imagecolorat($img, $x, $y);
            $alpha = ($colorxy >> 24) & 0xFF;
            //calculate new alpha
            if ($minalpha !== 127) {
                $alpha = 127 + 127 * $opacity * ($alpha - 127) / (127 - $minalpha);
            } else {
                $alpha += 127 * $opacity;
            }
            //get the color index with new alpha
            $alphacolorxy = imagecolorallocatealpha($img, ($colorxy >> 16) & 0xFF, ($colorxy >> 8) & 0xFF, $colorxy & 0xFF, $alpha);
            //set pixel with the new color + opacity
            if (!imagesetpixel($img, $x, $y, $alphacolorxy)) {
                return false;
            }
        }
    }

    return true;
}

Example of usage:

<?php
$image = imagecreatefrompng("img.png");
filter_opacity($image, 75);
header("content-type: image/png");
imagepng($image);
imagedestroy($image);

Source: http://php.net/manual/en/function.imagefilter.php

Farshad · Accepted Answer · 2014-09-16T04:46:48.477

2

Try to use this opensource PHP project:

Image workshop https://github.com/Sybio/ImageWorkshop

edited Sep 16 '14 at 04:46

answered Aug 23 '14 at 06:35

Farshad

1,465
1
9
12

I have tested this code with Gif file type for transparent image . try to test with tweeter icon in gif file type – Farshad Aug 23 '14 at 07:02
i have edited the code [Demo Link](http://farshadajdar.com/imgeditor/imgeditor.php?imgfile=bg.png) | [Source Code](http://farshadajdar.com/imgeditor/imgeditor.txt) – Farshad Aug 23 '14 at 07:57
I have edited the code above [Demo Link](http://farshadajdar.com/imgeditor/merged.png) | [Source Code](http://farshadajdar.com/imgeditor/imgeditor2.txt) – Farshad Aug 23 '14 at 10:04

imagecopyresampled with opacity

2 Answers2