How is the creation of PHP dynamic images implemented?

WITH-GD=[/PATH/TO/GD]
--WITH-JPEG-DIR=[/PATH/TO/JPEG-6B]
--with-t1lib=[/path/to/t1lib]
After you finish adding the Make command and then execute the make install command, restart Apache and run Phpinfo () to check that the new settings are in effect. Now we can start the image creation work.
Depending on the version of the GD library file that you installed, you will be able to create a graphics file in GIF or PNG format. If you are installing gd-1.6 or a previous version, you can use a GIF-formatted file, but you cannot create a PNG format, and if you install a later version of gd-1.6, you can create a PNG file but you cannot create a file in GIF format.
Creating a simple image also requires a number of functions, which we'll explain step-by-step.
In the following example, we will create a PNG-formatted image file, the following code is a header containing the MIME type of the created image:
? Header ("Content-type:image/png");
Use Imagecreate () to create a variable that represents a blank image, which requires an image-size parameter in pixels, in the format imagecreate (X_size, y_size). If you want to create an image with a size of 250x250, you can use the following statement:
$NEWIMG = Imagecreate (250,250);
Because the image is still blank, you might want to fill it with some color. You need to first use the Imagecolorallocate () function to specify a name for this color with its RGB value, which is formatted as imagecolorallocate ([image], [red], [green], [blue]). If you want to define azure, you can use the following statement:
$skyblue = Imagecolorallocate ($newImg, 136,193,255);
Next, you need to fill this image with this color using the Imagefill () function, which has several versions of the Imagefill () function, such as Imagefillrectangle (), Imagefillpolygon (), and so on. For the sake of simplicity, we use the Imagefill () function in the following format:
Imagefill ([Image], [Start x Point], [Start y point], [color])
Imagefill ($NEWIMG, 0,0, $skyblue);
Finally, after the image is established, release the image handle and the memory that is occupied:
Imagepng ($NEWIMG);
Imagedestroy ($NEWIMG);? >
In this way, all the code for creating the image looks like this:
? Header ("Content-type:image/png");
$NEWIMG = Imagecreate (250,250);
$skyblue = Imagecolorallocate ($newImg, 136,193,255);
Imagefill ($NEWIMG, 0,0, $skyblue);
Imagepng ($NEWIMG);
Imagedestroy ($NEWIMG);
? >
If you save this script file as skyblue.php and access it with a browser, we will see a turquoise 250x250 image in PNG format.
We can also use image creation functions to manipulate images, such as making a large image into a small image:
Suppose you have an image from which you want to crop a 35x35-sized image. All you need to do is create a blank image of 35x35 size, create an image stream containing the original image, and then place a resized original image in a new blank image.
The key function to complete this task is imagecopyresized (), which requires the following format:
Imagecopyresized ([New Image handle],[original image handle],[new image x], [New Image Y], [original image x], [Original IM Age Y], [new Image X], [New Image y], [original image x], [original image y]).
? /* Send a header to let the browser know what type of content The file contains */
Header ("Content-type:image/png");
/* Create a variable that holds the height and width of the new image */
$newWidth = 35;
$newHeight = 35;
/* Create a new blank image of the given height and width */
$NEWIMG = Imagecreate ($newWidth, $newHeight);
/* Get data from the original larger image */
$ORIGIMG = Imagecreatefrompng ("Test.png");
/* Copy the resized image, using Imagesx (), Imagesy () to get the original image in X, y dimensions */
Imagecopyresized ($NEWIMG, $ORIGIMG, 0,0,0,0, $newWidth, $newHeight, Imagesx ($ORIGIMG), Imagesy ($ORIGIMG));
/* Create desired image, free memory */
Imagepng ($NEWIMG);
Imagedestroy ($NEWIMG);? >

How is the creation of PHP dynamic images implemented?