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I am applying Effect-gaussian blur on an Object with 50% Opacity. Instead of producing a smooth blur effect it ends up with a box around the shape.

why does this happen? Thank you.

enter image description here

enter image description here

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    ...and how can I prevent it; is your follow-up question perhaps? :) My advice would be to use a Feather rather than Gaussian Blur. That has the additional benefit of being a vector effect as opposed to the rasterised Gaussian Blur.
    – Vincent
    Nov 24 '21 at 10:48
  • Lol.. I just wanna know why did this happen , I ask too much question i know and feel sad if I dnt know the answer 🤦‍♀️ am trying what you suggested. Thank you Nov 24 '21 at 10:57
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    :) I'd point out, again, that a radial gradient would be less file-intensive and more versatile in this situation. :)
    – Scott
    Nov 24 '21 at 18:27
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My suspicion is that this has everything to do with the fact that Gaussian Blur is a rasterised effect. It basically converts your object into pixels (gasp!) and then applies a Photoshop effect to it—hence the 'Photoshop Effects' mention in the Effect menu.

As Pixels take up memory space and thus CPU power, it seems reasonable to create an upper limit to the size of the raster image that the effect creates. The default is relatively small, to keep Illustrator running smoothly.

To prevent, I lifted this from http://vectorboom.com/load/tips/basix/remove_gaussian_blur_limitation_in_illustrator/15-1-0-345:

Go to Effect > Document Raster Settings and tweak the value in the field that says 'Add: ____ around object'. Apparently, if you set this value to at least three times the radius of the Blur, the blur effect will not get clipped.

Do note that the value in the field is limited to 720px, most probably to create an upper limit to the amount of pixels in the rasterised effect.

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Seemingly you have already got an explanation and how to persuade Illustrator to be less stingy when deciding how big raster image will be generated as the result of Gaussian blur effect.

The already given workaround (=use Feather) doesn't expand the shape like Gaussian blur, but makes the edges thinner - you may need to make an offset path to get the blur look expanded.

Another workaround is use Gaussian blur but at first

  • make a hidden safety copy of the object
  • make a big no stroke, background colored circle around the object, say 300% of the object dimensions. Bring the object to top:

enter image description here

  • select the new transparent object and the object to be blurred, apply Object > Rasterize > Transparent background and high enough resolution
  • blur the rasterized shape - Gaussian blur is also a raster image, so you do not lose anything (assuming you have also the safety copy):

enter image description here

Consider to make big fuzzy shapes by applying gradients - radial ones in this case. They are vector objects; scaling doesn't spoil them. In the next image a big circle with radial gradient from white to 0% opaque white is placed below the full white circle:

enter image description here

Gradient stops need careful adjustment, blurring would be easier if it worked as wanted.

More complex shapes are possible if you use Gradient Mesh. Check it from Illustrator User's Guide.

If you can accept raster images to be mixed with your vector shapes consider also making the wanted effect in Photoshop. You can easily paste a vector shape from Illustrator into an empty image in Photoshop (assuming the empty image has transparent background and the needed resolution for your final usage), blur, draw more with brushes or process otherwise the shape.

Export the modified shape as PSD or PNG (see NOTE1) with transparent background and place the image back to Illustrator. Pasting it directly back unfortunately removes the transparency.

NOTE1: PNG is RGB only, PSD can have CMYK colors

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  • Am blessed to have this answer as well. Your answer helps me to strong my knowledge. Thank you so much. Nov 24 '21 at 13:09
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    “make a hidden safety copy of the object” – this is a bad habit. Unless you know you will need the original again, you should leave it to proper version control to get back the original in case something goes wrong. (One of the advantages of vector editing over raster is that VCS is much more efficient on it.) Nov 25 '21 at 9:36
  • Is there an object level version control in Illustrator? Maybe I have a serious knowlwdge hole. I have been lucky enough to succeed by keeping a spare copy which has been the next of the risky version in the layers panel and disabled. File level version control is a known thing.
    – user287001
    Nov 25 '21 at 11:10

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