Even am facing the same problem...
Only PNG24/32 supports Transparency, not PNG8.
My problem is that the PNG does not appear at all. I can see it in the editor but when i preview the file, its not there. So, I went ahead and used the jpg version of the same graphic and in Captivate, selected transparent background. I chose "white" and it worked. the jpg appears with a transparent background!
I was having the same problem today (with a 5KB file). I ended up using PS to re-save the .PNG in .GIF format instead. I still had to switch on the background transparency in Captivate. But it turned out relatively well. (Relative to the .JPG that I tried it with---the anti-aliasing with that file format was terrible.)
Scaling down the image worked for me
In my experience, Captivate 3 seems to interpret the transparency in an image as black if the file size is large. It seems to happen in the resizing compression. There are two ways I have found to overcome this:
1. The most effective is to reduce the file size to less than 100kb. For most Captivate projects this still offers a good quality resolution in PNG format.
2. Using PhotoShop, lock the transparency then save the file again. If the save was previously interlaced then choose the opposite (none) this time – reverse if interlaced previously. Then reimport the file. This is not always effective but for some quirky reason, sometimes it works. It will not work with very large files but seems to work with stubborn smaller PNG files, where Captivate is interpreting transparency as black.
I hope this is of assistance to you.
The solution I've found is to just ensure that the image you're importing is smaller than the slide size. If Captivate has to resize or crop your image it (for some reason) interprets transparent space as black. Just resize the image to have a width and height less than that of the slide before importing and all should be well.
I know this is an old thread, but I just came across this problem and found a different solution that I thought I would share just in case it helps someone else.
I used the same custom png button with a transparent background (made in fireworks) for more than 50 projects with no problem. Suddenly, the black background (with a white border) that others mentioned appeared on the 56th project but only after it was published. It all appeared fine in the workspace. None of the solutions above would work.
my solution: I just merged the image button into the background and then placed a transparent button over it to create the action that I needed. Hope that helps someone in the future!
I found solution where I was having the same problem on browsers.
Problem at my end:
I was creating a transparent png's with image editor for web but in internet browsers it was showing a black background instead of transparent background.
Solution as per:
I find problem in my css file. Please check 'img' class in css modify or delete. it will remove the background.
I am using Captivate 5. My .png files were not transparent in the web browser exports. The problem was in the properties of the image. Uncheck "Allow Smoothing" and the gradient transparencies all work. This also resolved an issue with transparent text captions that were placed on layers above the .png showing color flashes during transitions.
Make sure you have an empty layer below the cropped image before you save as a .png. Turn off the visibility of the layer below before you output. Do not use the "Save for web and devices feature, make sure you use File/Save as...
I'm assuming you're creating the image in PS.
1. Open in Photoshop
2. Image > Mode > RGB / CMYK
Seems that Indexed Colors were causing the problem on my end.
OMG who is still using Indexed Colors nowadays? They are only 8-bit. I abandoned them over 15years ago. Sorry, for the exclamation but you should have seen the question marks in my eyes!
I still use them extensively if I don't need the color depth. Not so much for Captivate but definitely in HTML pages.
Try double klicking on your "background" layer in your layers palette, to make it into a layer, layer 0 by default. You shouldn't have any proplems after that.
Hope it helps!