Hello,
When picture background has just one color, is there in Inkscape a simple way to pick transparency index from this background (JPG) and to save picture with transparent background (PNG)?
Ps.: I am looking for a simple way that isn’t necessary to use Bezier tool around picture, since the background color is single.
Thanks in advance,
Cadu

Welcome Cadu!

If the background has enough contrast to the subject, you can use this method: http://tavmjong.free.fr/INKSCAPE/MANUAL ... -SIOX.html. I don't know how it works, or if it takes a transparency index from the background. And you do still have to draw a rectangle around the image, but it's not like tracing a complex line. After the trace is complete, and assuming it's successful, you can use File menu > Export Bitmap, which will save a PNG image with transparency intact.

If the background does'nt have enough contrast for the SIOX technique to work, you might be able to use a raster graphics program (The GIMP is free and open source) and change the background color, before importing to Inkscape.

I hope it works, but let us know if you run into any problems

if you're not tied to using inkscape for this, then gimp has a select by color tool. but i'm pretty sure you can't have a jpg picture actually have crystal clear delineated areas of contrast colors, as the format is not designed for that, and produces dither dots at the interface of those contrast colors. hence even select by color (from a jpg) will produce dirty results. might be better off to trace bitmap in inkscape using single color, and clean up the result by hand. even this though is often a trade off between the time spent cleaning up and the quality of result...sometimes it's just better to trace by hand (using a tablet of course) for more realistic results.

Hi,
I made some tests in Gimp. To this usage (remove/create transparent background), Gimp works great when background is more homogeneous or single color. In these cases, it is just to make an selection and use in Gimp menu [ colours=>colour to alpha ]. The results are great and fast to any type of image (PNG, JPG, etc.). Just remembering that just PNG, TIFF and GIF offer transparency. Actually, I didn't go ahead with Inkscape method cause first time it sugested hard-work!!! But I am getting familiarized with Inkscape just now. I will try soon and comment/compare outputs.
Best,
Cadu

There's a PDF in this topic: viewtopic.php?f=6&t=6616 It's a tutorial I made, with an example of using the SIOX technique. (Look about 2/3 to 3/4 down the page.) But I think the tavmjong Guide shows an example as well. Oh yikes! I just looked up the example in the Guide, and it's pretty bad . Mine's a more successful example

Please do keep in mind that jpegs are not very good candidates for replacing background with transparency. Even if the background is a single color, or a set of colors that don't feature in the foreground, it's almost impossible (in jpeg) to have a clean silhouette of the background. Theres going to be a boundary of pixels here and there, spread around the silhouette edge. If you put this transparent background jpeg source picture onto any other background color, those stray pixels will show horribly. I've done something like this before. By way of cleaning up those stray pixels, before i knew it, I was (clumsily) editing the picture. Cleaning up stray pixels quickly becomes guessing and creating an outline, and it doesn't quite work from a picture that didn't have an outline everywhere to start with. All i'm saying is, beware of the time that this can eat up, producing less than satisfying images; in lieu of locating a suitable image in png/gif/tiff format to begin with. Or you may even save time by tracing over original, to create a new image, rather than cleaning up existing jpeg.
Hope this helps..or else just print it out, scrumple up into a ball, and throw into a waste basket.
Enjoy your vectors with inkscape.