In javascript there is function getImageData(), is there any function in PHP similar to that.
Have a look at the GD library functions:
http://www.php.net/manual/en/ref.image.php
EDIT:
Specifically, the getimagesize function for dimensions and more :)
EDIT
Hello again. This should help. You can get the RGB values of your image like so:
// the file
$file = 'test.gif';
// get the width and height of the image
list($width, $height) = getimagesize($file);
// create your image resource
$image = imagecreatefromgif($file);
// you could use the image width and height values here to
// iterate through each pixel using two nested for loops...
// or... set specific values for $x and $y
$x = 0;
$y = 0;
// get the colour index for the current pixel
$colourIndex = imagecolorat($image, $x, $y);
// get an array of human-readable RGB values
$colourValues = imagecolorsforindex($image, $colourIndex
// display RGB values
print_r($colourValues);
GD is your best bet:
http://php.net/manual/en/function.imagecreatefromjpeg.php
You'll need to know the type (png, jpg) before you start.
Related
In a recent competition I was given the task to extract binary data (another PNG) from a PNG image file's alpha channel. The data was encoded in such a way that if I read the values in the alpha channel for each pixel from the top left (e.g. 80,78,71,13,10,26,10) up to a specific point then the resulting data would form another image.
Initially I tried to complete this task using PHP, but I hit a roadblock that I could not overcome. Consider the code below:
function pad($hex){
return strlen($hex) < 2 ? "0$hex" : $hex;
}
$channel = '';
$image = 'image.png';
$ir = imagecreatefrompng($image);
imagesavealpha($ir, true);
list($width, $height) = getimagesize($image);
for ($y = 0; $y < $height; $y++){
for ($x = 0; $x < $width; $x++){
$pixel = imagecolorat($ir, $x, $y);
$colors = imagecolorsforindex($ir, $pixel);
$a = pad(dechex($colors['alpha']));
$channel.= $a;
}
}
After running this, I noticed that the output did not contain the PNG magic number, and I just didn't know what went wrong. After a bit of digging I found out that $colors['alpha'] only contained values less than or equal to 127. Due to the data having been encoded with a 0-255 range in mind, I could not find a way to extract it, and ended up (successfully) solving the problem with node.js instead.
So, my question is: Is there any way I could have read the PNG file's alpha channel that would have returned the values in a 0 to 255 range as opposed to 0-127, or is this a hard-coded limitation of PHP and/or GD?
For the record, I tried to use ($colors['alpha']/127)*255 in order to try and forge the value in the incorrect range to the correct one, but to no avail.
It is a limitation of GD. According to https://bitbucket.org/libgd/gd-libgd/issues/132/history-behind-7-bit-alpha-component, in GD source it says:
gd has only 7 bits of alpha channel resolution, and 127 is
transparent, 0 opaque. A moment of convenience, a lifetime of
compatibility.
If you install ImageMagick PHP extension, you can get the alpha value between 0-255 for a pixel (let's say with x=300 and y=490) like this:
$image = new Imagick(__DIR__ . DIRECTORY_SEPARATOR . 'image.png');
$x = 300;
$y = 490;
$pixel = $image->getImagePixelColor($x, $y);
$colors = $pixel->getColor(true);
echo 'Alpha value: ' . round($colors['a'] * 255, 0);
ImageMagick: https://www.imagemagick.org
ImageMagick for PHP (called Imagick): http://php.net/manual/en/book.imagick.php
In your code:
list($width, $height) = getimagesize($image);
references a variable '$image' that was not defined in the code.
using getimagesize means $image is a filename.
so this line get's width and height from a filename.
This line broke the code when I tested it.
You already have your answer, but this is for posterity.
Considering the code, I feel:
$width=imagesx ($ir);
$height=imagesy ($ir);
Would be more logical (and actually works)
I've scoured around the internet a fair bit and I can't seem to find any reference to what I am attempting to achieve... I fear that means I'm probably going about doing something the wrong way, but I'll pose this question here anyways in hopes that maybe I am not.
I would like to take an already generated image that has a rectangular selection already drawn on it via a specific color and a dynamic (but always rectangular) path, and crop or cut-out (and use) the inner area of that rectangular path.
Let's use an image generated by google maps as an example for this:
I thought perhaps the imagemagick library would hold a solution for this, but, I don't know if it's because I haven't quite narrowed down the exact key terms for what I am looking to do exactly, or if it's because it cannot (at least not simply) be done, but I haven't turned up any solutions.
Any solutions, advice, or smacks to the head are welcome.
[Please note that (for now) I would like to operate under the assumption that these images already exist, so any information regarding the pixel coordinates of the relative selection area on the image doesn't exist]
Your problem seems to boil down to this: How do I find a red rectangle in an image?
This is quite an open-ended problem, and could actually be quite difficult to solve. However, if the following assumptions can be made, then the task will be a lot easier:
The rectangle is drawn in pure RGB red (#ff0000).
The rectangle is aligned parallel with the image edges.
The image is saved in a lossless format like PNG.
The image contains no other pixels of this exact colour.
We know the width of the rectangle's edges.
The example you provided seems to tick all these boxes. Since it's stored as an 8-bit indexed color image, the first step would be to convert it into a true color image. This makes it easier to check the pixel values.
Then find the outermost edges of the frame, inset the coordinates by the frame width, and crop the image. Here's some code that will do this for you:
<?php
$src_img = 'er7RT.png';
$frame_color = 0xff0000;
$frame_width = 6;
// Load image and copy to true color image resource
$im = imagecreatefrompng($src_img);
$sw = imagesx($im);
$sh = imagesy($im);
$im1 = imagecreatetruecolor($sw, $sh);
imagecopy ($im1, $im, 0, 0, 0, 0, $sw, $sh);
imagedestroy($im);
// Get outer dimensions of frame.
// Assume the frame color appears nowhere else in the image.
$minx = $miny = 999999;
$maxx = $maxy = -$minx;
for ($x=0; $x<$sw; $x++) for ($y=$sh/20; $y<$sh; $y+=$sh/10) {
if (imagecolorat($im1,$x,$y)==$frame_color) { $minx = $x; break 2; }
}
for ($x=$sw-1; $x>=0; $x--) for ($y=$sh/20; $y<$sh; $y+=$sh/10) {
if (imagecolorat($im1,$x,$y)==$frame_color) { $maxx = $x; break 2; }
}
for ($y=0; $y<$sh; $y++) for ($x=$sw/20; $x<$sw; $x+=$sw/10) {
if (imagecolorat($im1,$x,$y)==$frame_color) { $miny = $y; break 2; }
}
for ($y=$sh-1; $y>=0; $y--) for ($x=$sw/20; $x<$sw; $x+=$sw/10) {
if (imagecolorat($im1,$x,$y)==$frame_color) { $maxy = $y; break 2; }
}
if ($minx>=$maxx || $miny>=$maxy) die("Couldn't locate frame");
// Subtract frame width to obtain crop region
$minx += $frame_width;
$maxx -= $frame_width;
$miny += $frame_width;
$maxy -= $frame_width;
// Create new image with cropped dimensions
$im2 = imagecreatetruecolor($maxx-$minx, $maxy-$miny);
imagecopy ($im2, $im1, 0, 0, $minx, $miny, $maxx-$minx, $maxy-$miny);
// Finish up
header("Content-Type: image/png");
imagepng($im2);
imagedestroy($im1);
imagedestroy($im2);
I tried a lot of methods to do that, but I still have a lot of troubles with that.
Is it possible to resize all images to fixed width and height?
I want every uploaded image with width>=200px and height>=260px to be resized to width=200px and height=260px, but I want to keep a bit of proportionality and if image is bigger than 200x260px to resize it proportionally and then to capture center of image 200x260px.
I just need idea to know where to start and what to do, but if you have an example I would like to see it. Thanks.
If you want to trim the image you can do in the following way:-
//Your Image
$imgSrc = "image.jpg";
//getting the image dimensions
list($width, $height) = getimagesize($imgSrc);
//saving the image into memory (for manipulation with GD Library)
$myImage = imagecreatefromjpeg($imgSrc);
// calculating the part of the image to use for thumbnail
if ($width > $height) {
$y = 0;
$x = ($width - $height) / 2;
$smallestSide = $height;
} else {
$x = 0;
$y = ($height - $width) / 2;
$smallestSide = $width;
}
// copying the part into thumbnail
$thumbSize = 100;
$thumb = imagecreatetruecolor($thumbSize, $thumbSize);
imagecopyresampled($thumb, $myImage, 0, 0, $x, $y, $thumbSize, $thumbSize, $smallestSide, $smallestSide);
//final output
header('Content-type: image/jpeg');
imagejpeg($thumb);
To begin writing the function, we have to declare it as such… Then we have to throw in our attributes. We want to restrict our image, so we have to let the function know the dimensions to which we want to restrict it, and we have to know what the original image size is to begin with (we’ll get to that part in a second).
<?php
function imageResize($width, $height, $target) {
//takes the larger size of the width and height and applies the
formula accordingly...this is so this script will work
dynamically with any size image
if ($width > $height) {
$percentage = ($target / $width);
} else {
$percentage = ($target / $height);
}
//gets the new value and applies the percentage, then rounds the value
$width = round($width * $percentage);
$height = round($height * $percentage);
//returns the new sizes in html image tag format...this is so you
can plug this function inside an image tag and just get the
return "width=\"$width\" height=\"$height\"";
}
?>
Before we take our new function on a test drive, we need to get the width and height of the image that we want to display. There is a magical command in PHP called getimagesize(). This command, used properly, will return the image width, height, type, and even the width and height in HTML image tag format (width=”x” height=”y”).
$mysock = getimagesize("images/sock001.jpg");
Now, $mysock is an array that holds vital information about the particular image we want to display. In index 0, we have the width ($mysock[0]), and in index 1, we have the height ($mysock[1]). That’s really all we need, in order to get what we want done. Want to see the function… well, function? Here we go!
Let’s say you want to display a list of your beautiful socks, but you want room on the page to show them neatly in a row, and to do that they cannot be larger than 150 pixels tall or wide.
<?php
//get the image size of the picture and load it into an array
$mysock = getimagesize("images/sock001.jpg");
?>
<!-using a standard html image tag, where you would have the
width and height, insert your new imageResize() function with
the correct attributes -->
<img src="images/sock001.jpg" <?php imageResize($mysock[0],
$mysock[1], 150); ?>>
That’s it! Now, no matter what the original file size, it will be restricted to no more than 150 pixels in width or height (or whatever you specify).
I have a jpeg image resource loaded into a variable in php. Given a grayscale value, like 6, how can I set a single, particular pixel to that grayscale value? My client has made it exceedingly clear that there is a big difference between grayscale and rgb.
Is this even doable in php with the GD library? If so, how?
Note: The script does indeed grayscale the entire image, but using an obscure algorithm. My script obtains the RGB for each pixel, and obtains the grayscale value corresponding to the algorithm. It just needs to now transform that pixel to that particular grayscale value.
You will probably find the the imagesetpixel function handy. The following is an example of how you could use it:
// $image = <GD image resource>
for($x = 0; $x < $width; x++)
{
for($y = 0; $y < $height; $y++)
{
$value = specialFunction($rgb_value);
// Depending on what the above function returns, the call below
// might have to be changed
$color = imagecolorallocate($image, $value, $value, $value);
imagesetpixel($image, $x, $y, $color);
}
}
Do you have access to the terminal or something along those lines to install Image Magick. If so, then you can could use the following
convert image.jpg -colorspace Gray image-bw.jpg
I'm not sure how to do it with the PHP GD Library sorry.
Just for fun I've been looking at how to use the GD library to create a colour palette from an image. So far I've used GD to resize a user uploaded image to an appropriate size for displaying on a webpage.
Now I'd like to be able to get about five or so different colours from the image that represent the range of colours present in it. Once I've done that I'd like to generate a complementary palette based upon those colours, which I can then use to colour different elements on the page.
Any help I can get about how I would find the initial colour palette would be much appreciated!
EDIT:
I've come to my own solution which you can see below.
Well I've spent a couple of days fiddling around and this is how I managed to build my colour palette. Its worked fairly well for me and you can change the size of the colour palette to return more or less colours from the image.
// The function takes in an image resource (the result from one
// of the GD imagecreate... functions) as well as a width and
// height for the size of colour palette you wish to create.
// This defaults to a 3x3, 9 block palette.
function build_palette($img_resource, $palette_w = 3, $palette_h = 3) {
$width = imagesx($img_resource);
$height = imagesy($img_resource);
// Calculate the width and height of each palette block
// based upon the size of the input image and the number
// of blocks.
$block_w = round($width / $palette_w);
$block_h = round($height / $palette_h);
for($y = 0; $y < $palette_h; $y++) {
for($x = 0; $x < $palette_w; $x++) {
// Calculate where to take an image sample from the soruce image.
$block_start_x = ($x * $block_w);
$block_start_y = ($y * $block_h);
// Create a blank 1x1 image into which we will copy
// the image sample.
$block = imagecreatetruecolor(1, 1);
imagecopyresampled($block, $img_resource, 0, 0, $block_start_x, $block_start_y, 1, 1, $block_w, $block_h);
// Convert the block to a palette image of just one colour.
imagetruecolortopalette($block, true, 1);
// Find the RGB value of the block's colour and save it
// to an array.
$colour_index = imagecolorat($block, 0, 0);
$rgb = imagecolorsforindex($block, $colour_index);
$colour_array[$x][$y]['r'] = $rgb['red'];
$colour_array[$x][$y]['g'] = $rgb['green'];
$colour_array[$x][$y]['b'] = $rgb['blue'];
imagedestroy($block);
}
}
imagedestroy($img_resource);
return $colour_array;
}
this may help you
<?php
$im = ImageCreateFromJpeg($source_file);
$imgw = imagesx($im);
$imgh = imagesy($im);
// n = total number or pixels
$n = $imgw*$imgh;
$colors = array();
for ($i=0; $i<$imgw; $i++)
{
for ($j=0; $j<$imgh; $j++)
{
$rgb = ImageColorAt($im, $i, $j);
if (isset($colors[$rgb])) {
$colors[$rgb]++;
}
else {
$colors[$rgb] = 1;
}
}
}
asort($colors);
print_r($colors);
The imagecolorat function will give you the colour value at a pixel which you can use to scan the image and create a colour histogram:
http://www.php.net/manual/en/function.imagecolorat.php