Transparency, Or No Transparency. That Is The Question.

When in doubt, quote the Bard...

I'm working on a filter that is supposed to handle the image one way if it has transparency, and another way if does not. The filter result will always have a transparent background.

However, I have been unable to figure out how to test for a transparent background. "Get Alpha" does find the transparency if there is one, providing a black and white result, but returns a pure white (alpha for the full image) if the image doesn't have a transparent background.

Is there anyway to do what I'm trying to do with components? Or will a user input for Use Transparency be required?

I went ahead and added a checkbox control for the user to tell the filter if the image has a transparent background. But I haven't submitted the filter, so I can change it...

There is a switch controlling the inputs. One is a color input with Allow Images sel ected. The other is the external Image input. (A third input is a demo mode pattern.)

I understand how to use both Get Alpha and Set Alpha.

What I want to do is have the filter determine if the input image has an alpha layer, (other than for the bounds of the image,) that is different fr om the result of running the image through a Threshold component.

To demonstrate:

Use one of the built-in preview images and enable the transparency. Run the image through both the Get Alpha and Threshold components in parallel, the black and white result for each each component will be different.



Now run the same preview image through those components after disabling the transparency. The result of the Threshold component will be the same, but the Get Alpha component result has changed. It's now all white.



Is it possible to choose whether to use the result of Get Alpha or Threshold based on the result of Get Alpha?

I've come to the conclusion it isn't. But I'd love to be proven wrong.

If you scale the Get alpha result to, say 5 % around the center of the image and blur it by 5 units and then pick the center point with Lookup, if the result is anything but pure white, there is information on the alpha channel.

You can then use the IF or even the Threshold component to choose from two different inputs depending on whether it is pure white or not.

If that is what you mean.

Yes, I just coded the same thing at the same time... I had thought of the blur, but not the scale, excellent idea ThreeDee & CF&M.

Here's a version using blur...

Alpha image test.ffxml

Glad to see that you found a method that works for what you need...

Quote
L.Adair wrote: CFandM, my version 4 FF wouldn't open your file. It said I needed a later version.

I built that filter in FF5 so just for the heck of it I installed FF4 version 406 and
put together that filter again.....
btw this does not use a blur I used a free gradient..

If And Or Else FF4 Version.ffxml

Thank you, CFandM, for the version 4 code. I pulled it into FF and tinkered with it.

My Kaleidoscope solution doesn't always work, if the image is white with a transparent background. Your Free Gradient solution doesn't work if an input image without transparency isn't the same ratio as the the filter is working with, (new image, from the file menu.) It "sees" the "missing" sections as alpha, so it bypasses the Threshold output.

I'm not sure what you mean when you say I could tweak Lookup to see b/w. However, I tried using Blend to input black into the Lookup Y input. I didn't see any difference. But while tinkering, I discovered inputting a shade of gray into Lookup Y seems to work for any image.

I need to do more testing, of course. But it may be the best solution.

Thanks again for all your help.

This thread is interesting and useful