From you quesion, it seems you are kinda new to GD, I will share some experence of mine,
maybe this is a bit off topic, but I think it will be helpful to someone new to GD like you:
Step 1, validate file. Use the following function to check if the $_FILES['image']['tmp_name'] file is valid file:
function getContentsFromImage($image) {
if (@is_file($image) == true) {
return file_get_contents($image);
} else {
throw new \Exception('Invalid image');
}
}
$contents = getContentsFromImage($_FILES['image']['tmp_name']);
Step 2, get file format Try the following function with finfo extension to check file format of the file(contents). You would say why don't you just use $_FILES["image"]["type"] to check file format? Because it ONLY check file extension not file contents, if someone rename a file originally called world.png to world.jpg, $_FILES["image"]["type"] will return jpeg not png, so $_FILES["image"]["type"] may return wrong result.
function getFormatFromContents($contents) {
$finfo = new \finfo();
$mimetype = $finfo->buffer($contents, FILEINFO_MIME_TYPE);
switch ($mimetype) {
case 'image/jpeg':
return 'jpeg';
break;
case 'image/png':
return 'png';
break;
case 'image/gif':
return 'gif';
break;
default:
throw new \Exception('Unknown or unsupported image format');
}
}
$format = getFormatFromContents($contents);
Step.3, Get GD resource Get GD resource from contents we have before:
function getGDResourceFromContents($contents) {
$resource = @imagecreatefromstring($contents);
if ($resource == false) {
throw new \Exception('Cannot process image');
}
return $resource;
}
$resource = getGDResourceFromContents($contents);
Step 4, get image dimension Now you can get image dimension with the following simple code:
$width = imagesx($resource);
$height = imagesy($resource);
Now, Let's see what variable we got from the original image then:
$contents, $format, $resource, $width, $height
OK, lets move on
Step 5, calculate resized image arguments This step is related to your question, the purpose of the following function is to get resize arguments for GD function imagecopyresampled(), the code is kinda long, but it works great, it even has three options: stretch, shrink, and fill.
stretch: output image's dimension is the same as the new dimension you set. Won't keep height/width ratio.
shrink: output image's dimension won't exceed the new dimension you give, and keep image height/width ratio.
fill: output image's dimension will be the same as new dimension you give, it will crop & resize image if needed, and keep image height/width ratio. This option is what you need in your question.
function getResizeArgs($width, $height, $newwidth, $newheight, $option) {
if ($option === 'stretch') {
if ($width === $newwidth && $height === $newheight) {
return false;
}
$dst_w = $newwidth;
$dst_h = $newheight;
$src_w = $width;
$src_h = $height;
$src_x = 0;
$src_y = 0;
} else if ($option === 'shrink') {
if ($width <= $newwidth && $height <= $newheight) {
return false;
} else if ($width / $height >= $newwidth / $newheight) {
$dst_w = $newwidth;
$dst_h = (int) round(($newwidth * $height) / $width);
} else {
$dst_w = (int) round(($newheight * $width) / $height);
$dst_h = $newheight;
}
$src_x = 0;
$src_y = 0;
$src_w = $width;
$src_h = $height;
} else if ($option === 'fill') {
if ($width === $newwidth && $height === $newheight) {
return false;
}
if ($width / $height >= $newwidth / $newheight) {
$src_w = (int) round(($newwidth * $height) / $newheight);
$src_h = $height;
$src_x = (int) round(($width - $src_w) / 2);
$src_y = 0;
} else {
$src_w = $width;
$src_h = (int) round(($width * $newheight) / $newwidth);
$src_x = 0;
$src_y = (int) round(($height - $src_h) / 2);
}
$dst_w = $newwidth;
$dst_h = $newheight;
}
if ($src_w < 1 || $src_h < 1) {
throw new \Exception('Image width or height is too small');
}
return array(
'dst_x' => 0,
'dst_y' => 0,
'src_x' => $src_x,
'src_y' => $src_y,
'dst_w' => $dst_w,
'dst_h' => $dst_h,
'src_w' => $src_w,
'src_h' => $src_h
);
}
$args = getResizeArgs($width, $height, 150, 170, 'fill');
Step 6, resize image Use $args, $width, $height, $format and $resource we got from above into the following function and get the new resource of the resized image:
function runResize($width, $height, $format, $resource, $args) {
if ($args === false) {
return; //if $args equal to false, this means no resize occurs;
}
$newimage = imagecreatetruecolor($args['dst_w'], $args['dst_h']);
if ($format === 'png') {
imagealphablending($newimage, false);
imagesavealpha($newimage, true);
$transparentindex = imagecolorallocatealpha($newimage, 255, 255, 255, 127);
imagefill($newimage, 0, 0, $transparentindex);
} else if ($format === 'gif') {
$transparentindex = imagecolorallocatealpha($newimage, 255, 255, 255, 127);
imagefill($newimage, 0, 0, $transparentindex);
imagecolortransparent($newimage, $transparentindex);
}
imagecopyresampled($newimage, $resource, $args['dst_x'], $args['dst_y'], $args['src_x'], $args['src_y'], $args['dst_w'], $args['dst_h'], $args['src_w'], $args['src_h']);
imagedestroy($resource);
return $newimage;
}
$newresource = runResize($width, $height, $format, $resource, $args);
Step 7, get new contents, Use the following function to get contents from the new GD resource:
function getContentsFromGDResource($resource, $format) {
ob_start();
switch ($format) {
case 'gif':
imagegif($resource);
break;
case 'jpeg':
imagejpeg($resource, NULL, 100);
break;
case 'png':
imagepng($resource, NULL, 9);
}
$contents = ob_get_contents();
ob_end_clean();
return $contents;
}
$newcontents = getContentsFromGDResource($newresource, $format);
Step 8 get extension, Use the following function to get extension of from image format(note, image format is not equal to image extension):
function getExtensionFromFormat($format) {
switch ($format) {
case 'gif':
return 'gif';
break;
case 'jpeg':
return 'jpg';
break;
case 'png':
return 'png';
}
}
$extension = getExtensionFromFormat($format);
Step 9 save image If we have a user named mike, you can do the following, it will save to the same folder as this php script:
$user_name = 'mike';
$filename = $user_name . '.' . $extension;
file_put_contents($filename, $newcontents);
Step 10 destroy resource Don't forget destroy GD resource!
imagedestroy($newresource);
or you can write all your code into a class, and simply use the following:
public function __destruct() {
@imagedestroy($this->resource);
}
TIPS
I recommend not to convert file format that user upload, you will meet many problems.
