how blurring a group avoids pixelation issues

[brynn]

Hi Friends,
While the comment itself is entirely appropriate, and I'm sure spaventapasseri will respond, I didn't want to start a potentially extended technical discussion there (since the comment area really isn't meant for that).

I'm curious about Lazur's comment on spaventapasseri's image, which is

Hi! That blurred shadow shows some inkscape issues, with that pixelated look. I know that's not a new work of yours, but for the notice anyone new to this, that can be avoided if you first put the "to be blurred" object into a group.

Lazur, I'm not sure what issues you mean, that can be avoided by blurring a group.  Could you post some examples  in this topic, that show the issues, and how grouping avoids it?

Thanks 

[Lazur]

It was discussed here:
http://www.inkscapeforum.com/viewtopic.php?f=5&t=13979

Off-Topic: show

Anyone tried to rotate and skew a blurred object?
(?)
The pixelation issue only appears through inkscape's rendering, it doesn't show up in exported images or the svg viewed in a browser.

As any decent web search engine will uncover, this is a known issue with the old renderer used in current stable versions. You can either increase the quality of the rendering (in the preferences), which will slow down rendering, or e.g. put the object inside a group, blur the group, and apply any transformations to the object itself, inside the group. Note that using the second workaround the filter effect will not be rotated (useful e.g. for shadow effects).

The pixelation of that image's shadow speaks for itself, I cannot get a better image to illustrate the problem.
If you blur the group, the rotation of the objects inside of the group won't affect the look of the blur filter.
I could see that look only inside inkscape, so maybe that wasn't an exported image, but a part of a screenshot.

Maybe there was another topic on that, better explaining the transformation/filter order as well but I remembered this one.

[brynn]

Aahh yes, I remember that.  But I don't understand what you see in spaventapasseri's image, that made you think he might have blurred individual objects, rather than a group.....or rotated (transformed) objects after blurring them (without grouping).  How can you tell, by looking at only a PNG, whether objects were blurred before or after transform?

There are 1 or 2 places where the blur seems less than other places, if you look very, very closely.  That might indicate they were blurred individually, but I can't make the leap to thinking they might have been rotated after blurring.  I'm just curious what caught your attention?

Also, you said:

The pixelation issue only appears through inkscape's rendering, it doesn't show up in exported images or the svg viewed in a browser.

In the same way we can't know when rotation occured, if it occurred, we can't know for sure whether the PNG was exported from Inkscape.  But I'd say it would be a good bet that it was.  Thus my confusion.

Also, in the months while I was putting this site together, I didn't work with Inkscape, almost at all.  I'm finally now getting back to many drawings I had set aside.  So maybe my skills are just rusty  ?

[Lazur]

Original image:

Closeup:


From that pixelated look it is clear that the transformation was applied on the blurred shadow.
This behaviour seems to happen with the pre-cairo renderer, and doesn't show up in exported images.
Thus it seems no way it was an exported image.

[brynn]

Fascinating! Absolutely fascinating!  He must have used some 3rd party screenshot app, directly from the Inkscape window then.  (such as Windows 7's Snipping Tool, or the like)

In the black and gold chart that you posted previously, I can't see the same kind of pixelation, even zooming the browser as high as it will go.  So you must have exported that chart?

Well now that topic at IF makes so much more sense.  I did not understand the issues you were discussing, without seeing the example of the abnormal pixelation.

Thank you for taking the time to explain. 

And now, I'm more anxious than ever for the new renderer!  The last I heard, devs were planning another bug fix release, after 0.48.4 (which I guess would be 0.48.5) before 0.49 comes out.  So it seems we must continue to wait patiently, happily drawing and exporting, all the while   

[Lazur]

Yes, that example image was an exported one.
In the linked topic with that png the original svg was attached.

The blurring issue can be avoided at all by the grouping.
Until 0.49-... comes out, the best thing is that brand new 64bit version in my opinion.
Didn't tried it yet though, but I'm hoping it can work with large raster files.

[brynn]

Wow, this is the 1st I've heard of that.  Since I do use Inkscape on Win7, 64-bit, and have several very large, heavy projects, I'll have to check it out right away!  Thank for mentioning it.