Hi
I'm curious why, when you blur a Fill, some of the blur falls outside the border or path. I understand that happens when you blur a Stroke, because part of the stroke also falls outside the border/path. But when you select an object or path, and fill it with a gradient, the gradient stops at the border/path. Why doesn't the Blur stop at the border/path, when it's the Fill that's blurred?

Thanks for helping me understand

The answer is because it's blurred

Think of it this way, if you had a object that's half red and half blue. If you blurred it you would agree that the red should bleed into the blue as much as the blue should bleed into the red. Now what if the object was half red and half transparent? You've suggested the red should not blur into the transparent area at all, but this conflicts with what we expect in the red/blue example.

As a practical matter, after blurring an object I will often use an unblurred duplicate to clip the blurred object, effectively sealing the blur within the boundaries of the path.

Using a clone is somewhat nicer and it also results in more compact markup.

I still don't know how a clone is different from a duplicate, or even where the clone option is. I would do it micro's way.

And who cares about the markup?

In what way is a clone nicer than using a duplicate to clip?

btw, clone is under edit menu. the main difference is clone is "linked" to original object where duplicate is not. Thus if you change the original object somehow, the clone would be updated automatically but the duplicate would not.

Did I just answer my own question above? Hmm. Aho, are there other reasons you prefer clone or just the ease of updating the image?

Hi again,
Yes, I have thought that using a clip would eliminate the part of the blur that falls outside the border/path. And I also appreciate the discussion about duplicates and clones. I'm sure it will be helpful. But I'm kinda lost as to how it pertains to my question.

Micro, I do follow your example, but can't quite make the leap to how it answers my question. Here's a quick sample to illustrate my question better.

On the left, the white gradient stops at the border/path of the circle. On the right, the blurred white fill escapes the border/path of the circle. I want to know why doesn't the border/path stop the white blur from bleeding into the blue, like it stops the white gradient of the circle on the left, from showing outsidee the border/path.

I understand what you mean about the blue going into the red. Yes, that's what I would expect, within an object. But I'm asking why the blurred blue and red would fall outside the border of the object which the blue and red fills.

I might also comment that I understand how having a blur fall outside the border of an object or path can be useful. Indeed, I've used the blur to create successful highlights. But in my mind, which as a reminder, is not trained or very experienced at all, with computer graphics. To me, there are other ways to create highlights without the Blurring a Fill. For example, gradients can be used, OR blurred Strokes could be used. And to me, if would be more helpful if the blur of a Fill did not fall outside the border or path of an object. I just want to understand, if possible, why it does.

I also understand that I may not be able to comprehend the answer. It may just be that Blur a computer graphics standard, and Inkscape wants to provide it as an option, or to keep on par with the standards. But there are also many, many ways by which Inkscape does things differently than most other graphics programs. So I'm asking if there's a particular reason why Inkscape has designed the Blur to fall outside the border/path of the object it Fills.

I hope this clarifies my question. And thanks for your patience, as I continue to struggle with learning how to use Inkscape.

My understanding is that the object itself has been blurred, meaning the boundary is also blurred. My initial comment was intended to show how you could obtain the behavior you wanted with two simple steps->duplicate (or clone)->clip. We did get off on a tangent a bit, sorry.

The difference between the gradient and the blur is this: In the case of the gradient, the fill is a gradient. But in the case of the blur, the fill is not a blur - instead, the blur is something that is added afterwards, and applies to the object as a whole.

sas wrote:the blur is something that is added afterwards, and applies to the object as a whole.

I think that hits the nail on the head--you're bluring the object not the fill.

If you draw a red square in Inkscape and unfocus you eyes, the effect you see is intended to be the same as if you applied the blur effect and kept your eyes focused.

You are right that all graphics software behave this way.

You can also get a clipped blur using a filter effect, which means you don't need to use a duplicate or a clone, the clip is always correct no matter how you edit the object, and you can easily apply it to any object you want after creating the filter. Here's how:

1. Create a new filter effect.
2. Add Gaussian Blur to the effect, with whatever blur amount you want. That can be changed later, too.
3. Add Composite to the effect, with the following settings:
   
   • Top source is the result of the Gaussian Blur.
   • Bottom source is the Source Graphic.
   • Operator is "In".

The "In" operator clips the top source to the shape of the bottom source. So the blur gets clipped to the original shape. Just what we want!

Here's a screenshot of the filter in case my description isn't sufficient:

Ok, I guess I understand as much as I possibly can, at this point in my graphics "journey". Thanks for your comments, and for helping me understand this I truly appreciate your help!

No problem about going slightly OT, llog and others. Your discussion really is helpful to me. Especially kelan, I've played around with the Filter Effects some, but it's a totally alien (to me) dialog. Your step by step approach is very helpful, in a broader sense, for using Filter Effects in general. But I also look forward to trying the technique you describe for highlights!

So anyway, thanks again to all who replied