Reminder: Duplicate() Does Not Work With ColdFusion Images

Someone contacted me this morning needing help debugging an image thumbnailing problem. Part of the issue that they were running into was that the Duplicate() function did not seem to work with ColdFusion image objects. This can be confusing since the documentation seems to indicate that it will work:

Task: Create a ColdFusion image from another ColdFusion image.

Functions and Tags: ImageCopy function with the ImageWrite function or the Duplicate function, or by passing the image to the ImageNew function or the cfimage tag.

This language is quite awkward and a little ambiguous; but, it does seem to state that there are many ways to duplicate a ColdFusion image object. Unfortunately, most of these don't actually work - at least not in the way that I have interpreted them.

Let's run though a few demos. First, we are going to read in a picture of the beautiful, sexy, two-time Olympic Gold medalist, and "Dancing With The Stars" celebrity, Misty May. Then, we are going to duplicate Misty May's image using ColdFusion's Duplicate() method. Then we are going to add a caption to both images and write them to the browser:

When we run this code, we get the following output:

Notice that the second caption written to the duplicate image was actually written to both images. This is because the Duplicate() method only creates a copy of the image reference, not a copy of the underlying binary data. It seems as if Duplicate() is no different than simply assigning the image to two variables.

So, Duplicate() clearly doesn't work. But what about the other techniques mentioned in the documentation above? Let's try "passing the image to the ImageNew function":

This gives us the same output as above.

OK, but what about "by passing the image to the ImageNew function or the cfimage tag":

Unfortunately, this also gives us the same output as above. It looks like so far 3 out of the 4 methods in the documentation don't actually do anything.

It turns out, the ImageCopy() method is the only one of the documented techniques that works. To demonstrate this, let's create a ColdFusion user defined function that wraps around the ImageCopy() method:

With this method in place, we can now replace our duplication line with the following:

With this code in place, when we re-run the above demo, we get the following output:

As you can see, each of the above image now has the appropriate caption. This is because the second caption is written to the duplicate image which, thanks to ImageCopy() was not a reference to the original image.

There's nothing wrong with doing something like reading a file in to memory more than once if you need to create a duplicate; I've done that a bunch of times. But, when it comes to creating a duplicate ColdFusion image from an existing ColdFusion image, ImageCopy() is the only method that I have been able to use successfully.

If you are interested in the ImageAddCaption() method, I just added it for testing purposes:

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