Help with .png bit depths?

[Jon G]

Hi,

I tried to export an an image as a 8-bit png, but it seems that Xara always exports pngs with transparency as 32-bit.

Could someone help me out, as I'm fairly sure that png's are supposed to allow transparency also in 8 bits.

tia,

.jon

[jens g.r. benthien]

In the export options there is a drop-down box at the left center/bottom area. Open it and select *True Color*. The default setting is *true color + alpha* =32 bit.

[Jon G]

Thanks Jens,

Maybe I was not clear with my problem - I need to make 8-bit pngs with one transparent color.

Now Xara always wants to make the pngs 32-bit, regardless of the amount of colours.

I'm not sure if I'm doing it right, as I can't get single colour transparency at all with pngs, if I choose the desired tp colour and tick transparency on the other tab, it's full opaque.

I can only get any transparency when the "make background transparent" is checked, which then logically requires alpha magic...

[jens g.r. benthien]

Ooooops, my apologies...

ok -> export dialog -> select 256 colors in the drop down box -> at the bottom right there is a glass icon -> click the left to make the background transparent -> export

or click the right glass -> make selected color (!) transparent -> export

[Jon G]

Right,

I think I found a bug in the export dialog.

Please try the methods Jens described, my Xara Xtreme 2.0e CD only gives tranparency when both background and selected colour are ticked as transparent, which makes the png 32-bit.

Make selected colour transparent does nothing, and the images I need don't have background.

Comments?

[Charles Moir]

Jon you're right that something is not quite right here, but I think it IS exporting 8-bit PNGs even though Windows reports the bit-depth as 32-bit. Firstly if you import the bitmap back into Xara it reports that it's a 8-bit colour depth. Secondly if you compare the file size to an equivalent GIF (which can only be 8-bit) then are almost identical. Whereas exporting as a real 32-bit PNG with alpha channel produces a much larger file (about twice the size).

So I think this means it is really an 8-bit PNG with single colour transparency, but that the bit-depth flag in the file is incorrect. Anyway it seems to work fine in everything I've tried, and is the same size as an 8-bit PNG.

And if I select several colours from the palette to be transparent, that seems to work correctly as well. i.e. it really is an 8-bit PNG with multiple transparent colours (no alpha channel).

[wW]

I need to use PNG more often. Seems like it's a format somewhere inbetween JPG, GIF & then some. The options are intimidating, but then again, I shouldn't be such a "kicken wing"...

Gary said that folks should be using PNG more often. I should have listened to Uncle gAry awhile back when he mentioned this. Shame on me...