imagecreatetruecolor()

(PHP 4 >= 4.0.6, PHP 5, PHP 7)

新建一个真彩色图像

说明

imagecreatetruecolor()返回一个图像标识符，代表了一幅大小为$x_size和$y_size的黑色图像。

是否定义了本函数取决于 PHP 和 GD 的版本。从 PHP 4.0.6 到 4.1.x 只要加载了 GD 模块本函数一直存在，但是在没有安装 GD2 的时候调用，PHP 将发出致命错误并退出。在 PHP 4.2.x 中此行为改为发出警告而不是错误。其它版本只在安装了正确的 GD 版本时定义了本函数。

参数

图像宽度。

图像高度。

返回值

成功后返回图象资源,失败后返回FALSE。

范例

新建一个新的 GD 图像流并输出图像

以上例程的输出类似于：

注释

Note:此函数需要 GD 2.0.1 或更高版本(推荐 2.0.28 及更高版本)。

参见

• imagedestroy()销毁一图像
• imagecreate()新建一个基于调色板的图像

If you want to create a *transparent* PNG image, where the background is fully transparent, and all draw operations happen on-top of this, then do the following:

What you do is create a true colour image, make sure that the alpha save-state is on, then fill the image with a colour that has had its alpha level set to fully transparent (127).
The resulting PNG from the code above will have a red circle on a fully transparent background (drag the image into Photoshop to see for yourself)

HOW THE CHECK THE MEMORY BEFORE CREATING AN IMAGE?
I worked on a script where I delt with large images. Very often the error "out of memory" occured. So I had to figure out, how to check the memory BEFORE creating an image. I didn't find a solution on the web, so I ran my own test script. It built lots of images to compute the needed memory. I found out, that the formula mem = x * y * channel was not enough. There was an additional multiplier that varied. As a result 1.7 worked best. So the formula is: mem = x * y * channel * 1.7.
I post this script here hoping it is useful to someone who will run into the same problems.

Taking the opportunity, I thank everyone here at php.net for the great manual and the useful user scripts.

I discovered when installing GD 2+ that ImageCreate() doesn't work well with JPEGS, it makes a true colour JPEG into a 16 colour mess when combining ImageCreateFromJPEG(). If you have GD 2+ you must use ImageCreateTrueColor() for things like thumbnails, etc.

If you want a simple way to mirror images, use the function I've included below.

Example Usage: 

A note to post by Justin Greer @ 18-Nov-2003 10:40:
While this information has already been posted by php at REMOVEreallynicejerk dot com @ 16-Sep-2002 12:01, I feel it neccesary to notice 'cause Justin's post is in the top and it can make people go the wrong way: Justin's way of detecting which imagecreate function to use is too complicated, while there's an easy standard way:

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