batch processing canvas texture

[Drakkenson]

I have recently had the need to have pictures with a frame around them. At present it is possible to obtain this by using "resize canvas" and setting it to values larger than the photo dimensions. It is also possible to set the colour of the canvas that is visible around the original picture.

However, it would be useful to have not only a solid colour for the canvas, but also an image, such as a picture frame or a pattern of some kind. For this, it would be nice to be able to specify an arbitrary image as canvas, as a possible option instead of the solid colour setting.

[Drakkenson]

Sorry for answering my own post.
As a continuation of the proposal regarding the canvas in batch processing mode, besides the possibility to set a picture as canvas, another useful option would be to be able to set a transparent canvas, for filetypes that support it, such as png. This could be useful in web page design and other places that require batch resizing. Of course, having these options in the single image resize tools(Image submenu) would also be nice.

[CoDEmanX]

@Drakkenson:
you can use the watermark function to add some sort of canvas image (thanks to alpha support).

another useful option would be to be able to set a transparent canvas

that's exactly what i'm looking for too!
I use the batch convert to resize the canvas of couple images. Unfortunately, you can pick a solid color for the canvas only. It would be very handy if one could select "alpha" as color, at least 100% transparency. Partial transparency would be even better of course.

I also tried to use the color 255,0,255 for the canvas and set it to transparent afterwards. It doesn't work 'cause you can't replace a color by transparency
If one opens each image, convert colors to 8bit and set a color to transparent one by one - that works. But i can't do this using the batch converter GUI.