New to Flash - Imported layers contain contents of lower layers?

Question

Hello.
I have just started using flash, and know next to nothing about some of its functions, so I apologise if I appear to ask questions with obvious answers.
Anyway, I am attempting to add animation to a previously created layered image, which I am importing from a .psd. The image is structured so that different layers contain translucent masks for objects below - e.g., an upper layer might contain a purple tint gradient which is overlayed on the layers below. I can open up this image in photoshop and it behaves as you might expect, but I'm having difficulties importing the image into flash. When I do, for some reason, the layer contents are modified so that some layers contain not only the contents previously in the layer, but the contents of everything below it, as if that layer and all layers below have been merged down into that one layer. The lower layers are still present, but any modifications made to them are not visible as they are blocked by lower layers. This does not seem to be true for all layers -  only those that previously contained elements with an alpha value anywhere between 0 and 255 - i.e., the mask layers. This makes it impossible to achieve my goal, as I am attempting to animate the objects beneath the masks.
I'm not sure entirely why this is happening - it seems to be flash converting my layers in a very unintuitive manner. If anybody can help me figure out how to get around this, I would be very grateful. Possibly I could import each layer one at a time and re-arrange them in flash, but this would be very time consuming, especially considering that I may want to add animation to multiple similar files in the future. As such, if there is a way to get the layers to import correctly as arranged in the .psd, then this would be extremely useful.
Thanks!
[moved from AS3 forum - not AS related]

Answer 1

What are you using to generate the PSD?
Flash's mask support is a bit tricky. In most versions of flash it works as an on/off switch. If a layer is marked as a mask layer, if there is ANY data (transparent or not, white or black or any color), it considers that you want to show that portion of the layers it masks. If there is no bitmap data of any kind in the area, it will NOT show that.
Pictures are much easier to explain. This behavior would be much different in Photoshop.
In Flash, say you start with a giant ugly stock rainbow square as the graphic you wish to mask:
Note in the timeline above I have a layer above named 'mask' and it's set to actually be a mask layer. In that layer I have this radial black/white gradient:
If I pasted that into the alpha channel of a layer in Photoshop it would gradient the pictures transparency based on the black/gray/white. In flash, it doesn't care about that. All it cares about is there "is" or "is not" data. Since there's data in a larger region than the image it is masking, it will show the whole rainbow square below it, unlike Photoshop:
There's the output, mask applied.
Now if I actually cut a square of "bitmap data" out of the middle of the mask, Flash will dutifully clip that area so you can't see it. No data = can't see. So my new mask:
Now due to there being "missing data" in that rectangular area it will cut out that portion of the rainbow box:
Does this clarify a bit about the simplicity of masks?
To get masks to work a bit more like Photoshop there's a bit of a code workaround we've all used for quite a long time. You can read it in many links of you search for AS3 gradient mask. Take a look at the code samples to see how.