Export JPG Opacity problem

[CS1]

Anyone have the following problem:

I have a rectangle on my page with 10% opacity.

When I export the image as a JPG, the rectangel appears as solid fill with no opacity why is this?

[CS1]

As you can see by the attached image, exprting as PDF works fine.

[CipesDesign]

CS1, I have also noticed some odd results when exporting VW's files, in which opacity settings lower than 100% have been used, as image files. While PDF looks as expected on screen, when I've printed from the PDF file the opacity adjusted objects seem to (sometimes) become solid. Just FYI, as I understand it: Opacity = 100% is the same as Transparency = 0%. The terminology can be a little tricky... P

[CS1]

Haha yeah I get ya.

Yeah I have noticed the same thing, appears transparent on screen then when printing comes out opaque.

I have also noticed that if you have a hatched object then place a rectangle over the top (even if only partially covers the hatched object) then change the opacity, the hatched object prints out all weird, I can copy the hatched object and beside the other one, and provided the transparent object doesnt cover it at all it appears fine.

[IanH]

I've come to the BB today to comment on this before seeing this.

When I am exporting plan views that use transparency, the export as image is showing solid fills, although it is fine, but very much slower, using PDF.

I'm pretty much sure that I have exported this particular file as an image in the past because it takes so long to rasterise the pdf in Photoshop. Something appears to be working intermittently or has recently got broken.

[islandmon]

check out:

http://en.wikipedia.org/wiki/Alpha_channel

http://en.wikipedia.org/wiki/Portable_Network_Graphics

http://en.wikipedia.org/wiki/PDF

[IanH]

Not quite sure of the relevance of alpha channels. Bit of a smokescreen if you ask me. It would be a bit different if you wanted to export as a layered image, but we don't.

If you have a set of vectors, at some point its going to have to be rasterised. During this rasterising process, the image may be 'flattened'. So direct opacity/alpha support is not needed in a flat raster file. Just like in photoshop where transparent layers are flattened with varying opacity when you export as jpeg, the opacity does not suddenly disappear just because you output as jpeg.

For example, you take a photo through a window. Just because jpeg cannot support alpha/transparency, its not going to mean that the glass window becomes solid when you take the photo with a digital camera. But this is exactly what is happening when in VW you export image - in any format.

Also, this problem persists with image file formats that do support transparency. Outputting as png or photoshop, formats that do support transparency, the same issue - easy to spot, go to export image and hit render and the transparency goes solid colour no matter what file format is chosen. And i'm not convinced its always been like this for formats other than jpeg.

In the past I normally have output as pdf, but my last large project took an hour to rasterize in photoshop at full resolution so on subsequent takes, I'm 90% sure that I used an image export in some format (likely to be photoshop) or other because I would remember having to wait an hour whilst photoshop rasterised the file and I have a couple of versions of full resolution plans with inbuilt flattened opacity.

I'm not convinced that there is an odd thing going on and that image transparency of some form or other has not suddenly stopped working 100% of the time. I'm not saying that NNA have broken something, it could quite easily be something in the Vista GDI subsystem or third party libraries that NNA use to rasterise vector files.

[IanH]

Confirmed as working as expected under 2009. Apparently never worked for image export in 2008, even with image file formats that supported transparency within the file unless you worked around the problem with say a pdf.

Edited October 13, 2008 by IanH