Trace Bitmap: Alpha rendered with white background

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Postby TrickyWidget » Sat Dec 28, 2013 6:40 am

Hello, all! Long time user, first time poster.

I'm using Trace Bitmap to vectorize some PNGs (with multi-scan color). For the most part it works fine, except I'm having trouble with the portions of the images that have transparency. They are all rendered as if they were against a white background and the alpha is lost. See attachments for before and after shots (placed over a grey background).

I've searched and searched, but I can't find anything that seems to address this. I've tried both using the Export Bitmap function in Inkscape and external converters, but all give the same result.

Ideally, I'd love to be able to retain the transparency. But failing that, at the very least I need to be able to choose which color it blends in. Does anyone know how to accomplish this?

Thank you very much!

Attachments

Original, transparency intact.

Original.png (17.05 KiB) Viewed 3310 times

Vectorized, alpha blended to white!

Vectorized.png (21.21 KiB) Viewed 3310 times

Re: Trace Bitmap: Alpha rendered with white background

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Postby Lazur » Sat Dec 28, 2013 10:17 am

Re: Trace Bitmap: Alpha rendered with white background

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Postby TrickyWidget » Sat Dec 28, 2013 11:07 am

Thanks for the response!

Lazur URH wrote:I'm curious how could you get the auto-trace to make gradients at all.
As far as I could see it produces a group of flat shaded paths atop eachother to represent colour transitions.
Or did it?

It did. I just did a lot of scans for a smooth look.

Lazur URH wrote:If you can't get the options to trace only the opaque parts, you can still use the node editor tool to select any traced paths of the unwanted anti-aliased transparent edge, and delete it.

Well, the transparent parts in question are actually shadows. (I can't post the actual graphics due to licensing restrictions.) So I'd strongly prefer to keep the shadows than need to re-create them. And even if I try to pull them out, the closer "shadow" paths also start becoming part of the rest of the image. So I either wind up with some white-ish shadow left, or parts of the main image missing.

Re: Trace Bitmap: Alpha rendered with white background

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Postby Polygon » Tue Dec 31, 2013 5:08 am

I´m not getting why you need to autotrace at all as Inkscape (and others) can´t determine transparency at all.
Drawing this shape isn´t too complicated.
Maybe the file will tell you something.

ATtransparent.svg

(28.76 KiB) Downloaded 227 times

path3810.png (9.4 KiB) Viewed 3255 times

Happy New Year!

Cheers
P.

Re: Trace Bitmap: Alpha rendered with white background

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Postby TrickyWidget » Tue Dec 31, 2013 10:47 pm

Polygon wrote:I´m not getting why you need to autotrace [that image] at all

I don't. I just used that as an easy and clear example of what I'm talking about. I can't post the actual art I'm working with due to licensing restrictions.

Polygon wrote:Inkscape (and others) can´t determine transparency at all.

I feared that might be the case. Do you know if there's any way to control how it flattens the image? (Instead of just assuming a white background.)

Thanks!

Re: Trace Bitmap: Alpha rendered with white background

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Postby Polygon » Wed Jan 01, 2014 8:02 pm

TrickyWidget wrote:I don't. I just used that as an easy and clear example of what I'm talking about. I can't post the actual art I'm working with due to licensing restrictions.

I feared that as well.

TrickyWidget wrote:I feared that might be the case. Do you know if there's any way to control how it flattens the image? (Instead of just assuming a white background.)
Thanks!

Sure - just get rid of all objects in the background - then save to PNG.

Cheers
P.