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I have the following piece of code:
define(RED_THESHOLD,100);
define(GREEN_THESHOLD,200);
define(BLUE_THESHOLD,100);
function thresholdImage(String $imgdata){
$original_limit = ini_get('memory_limit');
ini_set('memory_limit', '-1');
$imageResource = imagecreatefromstring($imgData);
// Limit red green and blue color channels here
}
But I do not know how I can apply the color the constants:
RED_THESHOLD
GREEN_THESHOLD
BLUE_THESHOLD
According to the classic algorithms I need to read pixel by pixel each channel and apply the threshold by the following piece of code (I use images red channel as an example):
$new_pixel_value = ($red_pixel_value>RED_THESHOLD)?RED_THESHOLD:$red_pixel_value;
Do you know how I can do this?
This can be done by finding the color index for each pixel, converting that into RGBA, then constraining those values, converting it back into a color index and setting the pixel.
<?php
const RED_THESHOLD = 255;
const GREEN_THESHOLD = 10;
const BLUE_THESHOLD = 10;
$image = imagecreatefrompng('test.png');
$maxX = imagesx($image);
$maxY = imagesy($image);
for ($y = 0; $y < $maxY; ++$y) {
for ($x = 0; $x < $maxX; ++$x) {
$existing = imagecolorsforindex($image, imagecolorat($image, $x, $y));
$red = ($existing['red'] > RED_THESHOLD) ? RED_THESHOLD : $existing['red'];
$green = ($existing['green'] > GREEN_THESHOLD) ? GREEN_THESHOLD : $existing['green'];
$blue = ($existing['blue'] > BLUE_THESHOLD) ? BLUE_THESHOLD : $existing['blue'];
$new = imagecolorexact($image, $red, $green, $blue);
imagesetpixel($image, $x, $y, $new);
}
}
imagepng($image, 'test2.png');
Here is a comparison picture:
I'm trying to convert a grayscale image to pure black and white in PHP using the GD library.
The purpose would be to detect the cervical cells within the image.
I'll leave the PHP code and a MatLab one (I wrote this code in MatLab and I'm trying to obtain the same result in PHP). Basically, I'm having trouble accessing each individual pixel's color and modifying it. sample image
PHP:
<?php
$im = imagecreatefromjpeg("celule.jpg");
function imagetograyscale($im)
{
if (imageistruecolor($im)) {
imagetruecolortopalette($im, false, 256);
}
for ($c = 0; $c < imagecolorstotal($im); $c++) {
$col = imagecolorsforindex($im, $c);
$gray = round(0.299 * $col['red'] + 0.587 * $col['green'] + 0.114 * $col['blue']);
imagecolorset($im, $c, $gray, $gray, $gray);
}
}
imagetograyscale($im);
//imagefilter($im, IMG_FILTER_CONTRAST, -255); //i'm not looking for this effect
header('Content-type: image/jpeg');
imagejpeg($im);
$C = imagesx($im); //width
$L = imagesy($im); //height
echo "Dimensiuni imagine: latime $C, inaltime $L <br>";
//scanning through the image
for($x = 0; $x < $L; $x++) { //each line
for($y = 0; $y < $C; $y++) { //each column
// pixel color at (x, y)
$color = imagecolorat($im, $y, $x);
$color = imagecolorsforindex($im, $color); //getting rgb values
$RED[$x][$y] = $color["red"]; //each rgb component
$GREEN[$x][$y] = $color["green"];
$BLUE[$x][$y] = $color["blue"];
}
}
?>
MATLAB:
clear all, clc, close all;
I = imread('celule.jpg');
imshow(I)
title('original');
a=rgb2gray(I);
figure;
imshow(a)
title('grayscale');
s=size(a);
for i=1:s(1)
for j=1:s(2)
if a(i,j)>190
a(i,j)=0;
else a(i,j)=255;
end
end
end
figure;
imshow(a)
title('pure black and white');
Here's a way to do that with gd:
#!/usr/bin/php -f
<?php
// Open image and get dimensions
$im = imagecreatefromjpeg("cellule.jpg");
$w = imagesx($im);
$h = imagesy($im);
// Convert to greyscale
imagefilter($im,IMG_FILTER_GRAYSCALE);
imagepng($im, "grey.png"); // DEBUG only
// Allocate a new palette image to hold the b&w output
$out = imagecreate($w,$h);
// Allocate b&w palette entries
$black = imagecolorallocate($out,0,0,0);
$white = imagecolorallocate($out,255,255,255);
// Iterate over all pixels, thresholding to pure b&w
for ($x = 0; $x < $w; $x++) {
for ($y = 0; $y < $h; $y++) {
// Get current color
$index = imagecolorat($im, $x, $y);
$grey = imagecolorsforindex($im, $index)['red'];
// Set pixel white if below threshold - don't bother settting black as image is initially black anyway
if ($grey <= 190) {
imagesetpixel($out,$x,$y,$white);
}
}
}
imagepng($out, "result.png");
?>
I didn't find anything about the subject, but I am dreaming vividly or is it possible in PHP to scan a PNG image and find the transparent positions in a picture?
for example, if there is a image of a TV with a transparent hole where the screen is. Can I find the most top-left, most top-right, most bottom-left, most bottom-right coordinates of transparent pixels by scanning the alpha-channel?
Not sure if there's a library doing this, I checked real quick but did not find..
Maybe not the most elegant solution and I'm sure there's a better way of doing it, but this works for a well-formed png image
// Returns the coordinates of a transparent rectangle in a PNG file (top left, top right, lower left, lower right
public function getTransparentRectangleCoordinates($fileUrl)
{
define ('TRANSPARENCY_THRESHOLD', 100); // 127=fully transparent, 0=black
$img = #imagecreatefrompng($fileUrl);
if (!$img) return ('Invalid PNG Image');
$coordLowestX = array(imagesx($img), '');
$coordHighestX = array(0, '');
$coordLowestY = array('', imagesy($img));
$coordHighestY = array('', 0);
$minX = imagesx($img);
$maxX = 0;
$minY = imagesy($img);
$maxY = 0;
// Scanning image pixels to find transparent points
for ($x=0; $x < imagesx($img); ++$x)
{
for ($y=0; $y < imagesy($img); ++$y)
{
$alpha = (imagecolorat($img, $x, $y) >> 24) & 0xFF;
if ($alpha >= TRANSPARENCY_THRESHOLD)
{
if ($x < $coordLowestX[0]) $coordLowestX = array($x, $y);
if ($x > $coordHighestX[0]) $coordHighestX = array($x, $y);
if ($y < $coordLowestY[1]) $coordLowestY = array($x, $y);
if ($y >= $coordHighestY[1]) $coordHighestY = array($x, $y);
if ($x < $minX) $minX = $x;
if ($x > $maxX) $maxX = $x;
if ($y < $minY) $minY = $y;
if ($y > $maxY) $maxY = $y;
}
}
}
// This means it's a non-rotated rectangle
if ( $coordLowestX == array($minX, $minY) )
{
$isRotated = false;
return array( array($minX, $minY), array($maxX, $minY), array($minX, $maxY), array($maxX, $maxY) );
}
// This means it's a rotated rectangle
else
{
$isRotated = true;
// Rotated counter-clockwise
if ($coordLowestX[1] < $coordHighestX[1])
return array($coordLowestX, $coordLowestY, $coordHighestY, $coordHighestX);
else // Rotated clockwise
return array($coordLowestY, $coordHighestY, $coordLowestX, $coordHighestX);
}
}
I've tried experimenting with the GD library to simulate Photoshop's muliply effect, but I haven't found a working solution yet.
According to Wikipedia, the multiply blend mode:
[...] multiplies the numbers for each pixel of the top layer with the corresponding pixel for the bottom layer. The result is a darker picture.
Does anyone know of a way to achieve this using PHP? Any help would be much appreciated.
You need to take every pixel of your image, then multiply each RGB value with your background color / 255 (it's the Photoshop formula). For example, a JPG file with a red background color multiply filter, saved as a PNG file for better results:
<?php
$filter_r=216;
$filter_g=0;
$filter_b=26;
$suffixe="_red";
$path=YOURPATHFILE;
if(is_file($path)){
$image=#imagecreatefromjpeg($path);
$new_path=substr($path,0,strlen($path)-4).$suffixe.".png";
$imagex = imagesx($image);
$imagey = imagesy($image);
for ($x = 0; $x <$imagex; ++$x) {
for ($y = 0; $y <$imagey; ++$y) {
$rgb = imagecolorat($image, $x, $y);
$TabColors=imagecolorsforindex ( $image , $rgb );
$color_r=floor($TabColors['red']*$filter_r/255);
$color_g=floor($TabColors['green']*$filter_g/255);
$color_b=floor($TabColors['blue']*$filter_b/255);
$newcol = imagecolorallocate($image, $color_r,$color_g,$color_b);
imagesetpixel($image, $x, $y, $newcol);
}
}
imagepng($image,$new_path);
}
?>
I've been looking for Multiply blend between two images as well and couldn't find any native-php solution for it. It appears that only way (for now) is to "manually" set pixels, pixel-by-pixel. Here's my code that does Multiply blend between two images, assuming that images are of the same size. You can adjust it to handle different sizes if you like.
function multiplyImage($dst,$src)
{
$ow = imagesx($dst);
$oh = imagesy($dst);
$inv255 = 1.0/255.0;
$c = imagecreatetruecolor($ow,$oh);
for ($x = 0; $x <$ow; ++$x)
{
for ($y = 0; $y <$oh; ++$y)
{
$rgb_src = imagecolorsforindex($src,imagecolorat($src, $x, $y));
$rgb_dst = imagecolorsforindex($dst,imagecolorat($dst, $x, $y));
$r = $rgb_src['red'] * $rgb_dst['red']*$inv255;
$g = $rgb_src['green'] * $rgb_dst['green']*$inv255;
$b = $rgb_src['blue'] * $rgb_dst['blue']*$inv255;
$rgb = imagecolorallocate($c,$r,$g,$b);
imagesetpixel($c, $x, $y, $rgb);
}
}
return $c;
}
Function returns image object so you should ensure to do imagedestroy after you're done using it.
There should be a workaround using overlay native-php blend, which suggests that 50% gray pixels of destination image will be affected by source pixels. In theory, if you do need to blend two black-and-white images (no gray tones), if you set contrast of destination image so white will become 50%-gray, and then overlay-blend source image over it, should give you something similar to multiply. But for color images, or grayscale images, this wouldn't work - above method appears to be the only option.
I was led into this thread when I needed to blend two images in GD. It seems there is no code specifically for that so I will just leave this here for future visitors to this page.
This is a fork from the answer of colivier that supports multiply-blending of two images.
The two images need not be of the same size BUT the overlaying image will be resized and cropped to the size of the bottom layer. I made a fit helper function to do just that but don't bother with that.
imagecolorat returns the base color, even with PNGs with transparency. That is, a 50% black (visible as (128, 128, 128)) will be returned as (0, 0, 0, 64) 64 being the alpha value. This code takes into consideration translucency and converts the translucent colors to the visible color values.
// bottom layer
$img1 = imagecreatefromjpeg(realpath(__DIR__.'/profilePic.jpg'));
// top layer
$img2 = imagecreatefrompng(realpath(__DIR__.'/border2.png'));
imagealphablending($img2, false);
imagesavealpha($img2, true);
$imagex = imagesx($img1);
$imagey = imagesy($img1);
$imagex2 = imagesx($img2);
$imagey2 = imagesy($img2);
// Prereq: Resize img2 to match img1, cropping beyond the aspect ratio
$w1 = max(min($imagex2, $imagex), $imagex);
$h1 = max(min($imagey2, $imagey), $imagey);
$w_using_h1 = round($h1 * $imagex2 / $imagey2);
$h_using_w1 = round($w1 * $imagey2 / $imagex2);
if ($w_using_h1 > $imagex) {
fit($img2, $imagex, $imagey, 'HEIGHT', true);
}
fit($img2, $imagex, $imagey, 'WIDTH', true);
// Actual multiply filter
for ($x = 0; $x < $imagex; ++$x) {
for ($y = 0; $y < $imagey; ++$y) {
$rgb1 = imagecolorat($img1, $x, $y);
$rgb2 = imagecolorat($img2, $x, $y);
$idx1 = imagecolorsforindex($img1, $rgb1);
$idx2 = imagecolorsforindex($img2, $rgb2);
// Shift left 8, then shift right 7
// same as multiply by 256 then divide by 128
// approximate multiply by 255 then divide by 127
// This is basically multiply by 2 but, expanded to show that
// we are adding a fraction of white to the translucent image
// $adder = ($idx2['alpha'] << 8 >> 7);
$adder = ($idx2['alpha'] << 1);
$rmul = min(255, $idx2['red'] + $adder);
$gmul = min(255, $idx2['green'] + $adder);
$bmul = min(255, $idx2['blue'] + $adder);
$color_r = floor($idx1['red'] * $rmul / 255);
$color_g = floor($idx1['green'] * $gmul / 255);
$color_b = floor($idx1['blue'] * $bmul / 255);
$newcol = imagecolorallocatealpha($img1, $color_r, $color_g, $color_b, 0);
imagesetpixel($img1, $x, $y, $newcol);
}
}
imagejpeg($img1, __DIR__.'/out.jpg');
/**
* Fits an image to a $w x $h canvas
*
* #param type $w Target width
* #param type $h Target height
* #param int $fit_which Which dimension to fit
* #param bool $upscale If set to true, will scale a smaller image to fit the given dimensions
* #param bool $padded If set to true, will add padding to achieve given dimensions
*
* #return Image object
*/
function fit(&$img, $w, $h, $fit_which = 'BOTH', $upscale = false, $padded = true) {
if (!in_array($fit_which, array('WIDTH', 'HEIGHT', 'BOTH'))) {
$fit_which = 'BOTH';
}
$w0 = imagesx($img);
$h0 = imagesy($img);
if (!$upscale && $w0 <= $w && $h0 <= $h)
return $this;
if ($padded) {
$w1 = max(min($w0, $w), $w);
$h1 = max(min($h0, $h), $h);
}
else {
$w1 = min($w0, $w);
$h1 = min($h0, $h);
}
$w_using_h1 = round($h1 * $w0 / $h0);
$h_using_w1 = round($w1 * $h0 / $w0);
// Assume width, crop height
if ($fit_which == 'WIDTH') {
$w2 = $w1;
$h2 = $h_using_w1;
}
// Assume height, crop width
elseif ($fit_which == 'HEIGHT') {
$w2 = $w_using_h1;
$h2 = $h1;
}
elseif ($fit_which == 'BOTH') {
if (!$padded) {
$w2 = $w = min($w, $w_using_h1);
$h2 = $h = min($h, $h_using_w1);
}
else {
// Extend vertically
if ($h_using_w1 <= $h) {
$w2 = $w1;
$h2 = $h_using_w1;
}
// Extend horizontally
else {
$w2 = $w_using_h1;
$h2 = $h1;
}
}
}
$im2 = imagecreatetruecolor($w, $h);
imagealphablending($im2, true);
imagesavealpha($im2, true);
$transparent = imagecolorallocatealpha($im2, 255, 255, 255, 127);
imagefill($im2, 0, 0, $transparent);
imagealphablending($img, true);
imagesavealpha($img, true);
// imagefill($im, 0, 0, $transparent);
imagecopyresampled($im2, $img, ($w - $w2) / 2, ($h - $h2) / 2, 0, 0, $w2, $h2, $w0, $h0);
$img = $im2;
}
Have you tried to use php manual?
For people looking to apply a 'multiply' effect on images like the one in Photoshop (generally b&w ones), you can achieve it with the IMG_FILTER_COLORIZE filter.
<?php
function multiplyColor(&$im, $color = array(255, 0, 0)) {
//get opposite color
$opposite = array(255 - $color[0], 255 - $color[1], 255 - $color[2]);
//now we subtract the opposite color from the image
imagefilter($im, IMG_FILTER_COLORIZE, -$opposite[0], -$opposite[1], -$opposite[2]);
}
?>
If used with png image and alpha must be well and works very well
$filter_r=215;
$filter_g=5;
$filter_b=5;
$alpha=70;
$suffixe="_red";
$path="./img/foto_220_590.png";
if(is_file($path)){
$image=imagecreatefrompng($path);
$new_path=substr($path,0,strlen($path)-4).$suffixe.".png";
echo $imagex = imagesx($image);
echo $imagey = imagesy($image);
for ($x = 0; $x <$imagex; ++$x) {
for ($y = 0; $y <$imagey; ++$y) {
$rgb = imagecolorat($image, $x, $y);
$TabColors=imagecolorsforindex ( $image , $rgb );
$color_r=floor($TabColors['red']*$filter_r/255);
$color_g=floor($TabColors['green']*$filter_g/255);
$color_b=floor($TabColors['blue']*$filter_b/255);
//$newcol = imagecolorallocate($image, $color_r,$color_g,$color_b);
// this new alpha
$newcol = imagecolorallocatealpha($image, $color_r,$color_g,$color_b,$alpha);
imagesetpixel($image, $x, $y, $newcol);
}
}
imagepng($image,$new_path);
I updated #colivier script to be able to myltiply two images, and not just an image with a color:
/**
* Multiply $pathToDst and $pathToSrc to $resultPath
*
* #param string $pathToDst
* #param string $pathToSrc
* #param string $resultPath
*/
function multiply($pathToDst, $pathToSrc, $resultPath) {
switch (pathinfo($pathToDst, PATHINFO_EXTENSION)) {
case "gif" :
$resourceDst = imagecreatefromgif($pathToDst);
break;
case "png" :
$resourceDst = imagecreatefrompng($pathToDst);
break;
default :
$resourceDst = imagecreatefromjpeg($pathToDst);
break;
}
switch (pathinfo($pathToSrc, PATHINFO_EXTENSION)) {
case "gif" :
$resourceSrc = imagecreatefromgif($pathToSrc);
break;
case "png" :
$resourceSrc = imagecreatefrompng($pathToSrc);
break;
default :
$resourceSrc = imagecreatefromjpeg($pathToSrc);
break;
}
for ($x = 0; $x < 400; ++$x) {
for ($y = 0; $y < 400; ++$y) {
$TabColorsFlag = imagecolorsforindex($resourceDst, imagecolorat($resourceDst, $x, $y));
$TabColorsPerso = imagecolorsforindex($resourceSrc, imagecolorat($resourceSrc, $x, $y));
$color_r = floor($TabColorsFlag['red'] * $TabColorsPerso['red'] / 255);
$color_g = floor($TabColorsFlag['green'] * $TabColorsPerso['green'] / 255);
$color_b = floor($TabColorsFlag['blue'] * $TabColorsPerso['blue'] / 255);
imagesetpixel($resourceDst, $x, $y, imagecolorallocate($resourceSrc, $color_r, $color_g, $color_b));
}
}
imagepng($resourceDst, $resultPath, 0);
imagedestroy($resourceDst);
imagedestroy($resourceSrc);
}
How do I check if a PNG image has transparent pixels using PHP's GD extension?
I know this is old, but I just found this on the comments of the PHP docs. (link)
Here is the function which determines whether the PNG image contains alpha or not:
<?php
function is_alpha_png($fn){
return (ord(#file_get_contents($fn, NULL, NULL, 25, 1)) == 6);
}
?>
The color type of PNG image is stored at byte offset 25. Possible values of that 25'th byte is:
0 - greyscale
2 - RGB
3 - RGB with palette
4 - greyscale + alpha
6 - RGB + alpha
Only works for PNG images though.
It doesn't look like you can detect transparency at a glance.
The comments on the imagecolorat manual page suggest that the resulting integer when working with a true-color image can actually be shifted four times total, with the fourth being the alpha channel (the other three being red, green and blue). Therefore, given any pixel location at $x and $y, you can detect alpha using:
$rgba = imagecolorat($im,$x,$y);
$alpha = ($rgba & 0x7F000000) >> 24;
$red = ($rgba & 0xFF0000) >> 16;
$green = ($rgba & 0x00FF00) >> 8;
$blue = ($rgba & 0x0000FF);
An $alpha of 127 is apparently completely transparent, while zero is completely opaque.
Unfortunately you might need to process every single pixel in the image just to find one that is transparent, and then this only works with true-color images. Otherwise imagecolorat returns a color index, which you must then look up using imagecolorsforindex, which actually returns an array with an alpha value.
I know this is an old thread, but in my opinion it needs improvement since walking through a huge png by checking all pixels only to find out it is not transparent is a waste of time. So after some googleing I found Jon Fox's Blog and I improved his code with the help of the W3C PNG Specification further to be reliable, fast and have a minimum on memory imprint:
function IsTransparentPng($File){
//32-bit pngs
//4 checks for greyscale + alpha and RGB + alpha
if ((ord(file_get_contents($File, false, null, 25, 1)) & 4)>0){
return true;
}
//8 bit pngs
$fd=fopen($File, 'r');
$continue=true;
$plte=false;
$trns=false;
$idat=false;
while($continue===true){
$continue=false;
$line=fread($fd, 1024);
if ($plte===false){
$plte=(stripos($line, 'PLTE')!==false);
}
if ($trns===false){
$trns=(stripos($line, 'tRNS')!==false);
}
if ($idat===false){
$idat=(stripos($line, 'IDAT')!==false);
}
if ($idat===false and !($plte===true and $trns===true)){
$continue=true;
}
}
fclose($fd);
return ($plte===true and $trns===true);
}
It can be done!
I've combined all answers and comments into one function which should be fast & reliable:
function hasAlpha($imgdata) {
$w = imagesx($imgdata);
$h = imagesy($imgdata);
if($w>50 || $h>50){ //resize the image to save processing if larger than 50px:
$thumb = imagecreatetruecolor(10, 10);
imagealphablending($thumb, FALSE);
imagecopyresized( $thumb, $imgdata, 0, 0, 0, 0, 10, 10, $w, $h );
$imgdata = $thumb;
$w = imagesx($imgdata);
$h = imagesy($imgdata);
}
//run through pixels until transparent pixel is found:
for($i = 0; $i<$w; $i++) {
for($j = 0; $j < $h; $j++) {
$rgba = imagecolorat($imgdata, $i, $j);
if(($rgba & 0x7F000000) >> 24) return true;
}
}
return false;
}
//SAMPLE USE:
hasAlpha( imagecreatefrompng("myfile.png") ); //returns true if img has transparency
Pretty strait forward function, it will check if there is any transparent pixel in the image, if it is, it will return true.
$im = imagecreatefrompng('./transparent.png');
if(check_transparent($im)) {
echo 'DA';
}
else {
echo 'NU';
}
function check_transparent($im) {
$width = imagesx($im); // Get the width of the image
$height = imagesy($im); // Get the height of the image
// We run the image pixel by pixel and as soon as we find a transparent pixel we stop and return true.
for($i = 0; $i < $width; $i++) {
for($j = 0; $j < $height; $j++) {
$rgba = imagecolorat($im, $i, $j);
if(($rgba & 0x7F000000) >> 24) {
return true;
}
}
}
// If we dont find any pixel the function will return false.
return false;
}
This is how I detect 8-32 bit transparency. It only work with PNG's.
function detect_transparency($file){
if(!#getimagesize($file)) return false;
if(ord(file_get_contents($file, false, null, 25, 1)) & 4) return true;
$content = file_get_contents($file);
if(stripos($content,'PLTE') !== false && stripos($content, 'tRNS') !== false) return true;
return false;
}
cronoklee's function is very good, but when I was using it I found a bug. It does not work for images with 8 bit pallet. Here is the fixed variant:
public function hasAlpha($imgdata)
{
$w = imagesx($imgdata);
$h = imagesy($imgdata);
if($w>100 || $h>100){ //resize the image to save processing
$thumb = imagecreatetruecolor(100, 100);
imagealphablending($thumb, FALSE);
imagecopyresized( $thumb, $imgdata, 0, 0, 0, 0, 100, 100, $w, $h );
$imgdata = $thumb;
$w = imagesx($imgdata);
$h = imagesy($imgdata);
}
//run through pixels until transparent pixel is found:
for($i = 0; $i<$w; $i++) {
for($j = 0; $j < $h; $j++) {
$ci = imagecolorat($imgdata, $i, $j);
$rgba = imagecolorsforindex($imgdata, $ci);
if($rgba['alpha']) { return true; }
}
}
return false;
}
Improved cronoklee's function. Removed unnecessary bit shifting for each pixel, reduced false negatives count, added explanation in function description.
/**
* Estimates, if image has pixels with transparency. It shrinks image to 64 times smaller
* size, if necessary, and searches for the first pixel with non-zero alpha byte.
* If image has 1% opacity, it will be detected. If any block of 8x8 pixels has at least
* one semi-opaque pixel, the block will trigger positive result. There are still cases,
* where image with hardly noticeable transparency will be reported as non-transparent,
* but it's almost always safe to fill such image with monotonic background.
*
* Icons with size <= 64x64 (or having square <= 4096 pixels) are fully scanned with
* absolutely reliable result.
*
* #param resource $image
* #return bool
*/
function hasTransparency ($image): bool {
if (!is_resource($image)) {
throw new \InvalidArgumentException("Image resource expected. Got: " . gettype($image));
}
$shrinkFactor = 64.0;
$minSquareToShrink = 64.0 * 64.0;
$width = imagesx($image);
$height = imagesy($image);
$square = $width * $height;
if ($square <= $minSquareToShrink) {
[$thumb, $thumbWidth, $thumbHeight] = [$image, $width, $height];
} else {
$thumbSquare = $square / $shrinkFactor;
$thumbWidth = (int) round($width / sqrt($shrinkFactor));
$thumbWidth < 1 and $thumbWidth = 1;
$thumbHeight = (int) round($thumbSquare / $thumbWidth);
$thumb = imagecreatetruecolor($thumbWidth, $thumbHeight);
imagealphablending($thumb, false);
imagecopyresized($thumb, $image, 0, 0, 0, 0, $thumbWidth, $thumbHeight, $width, $height);
}
for ($i = 0; $i < $thumbWidth; $i++) {
for ($j = 0; $j < $thumbHeight; $j++) {
if (imagecolorat($thumb, $i, $j) & 0x7F000000) {
return true;
}
}
}
return false;
}
Usage:
hasTransparency( imagecreatefrompng("myfile.png") ); //returns true if img has transparency