Non-existing space "showing up" when cutting objects

[Devotee]

Hello.

Im doing a self-portrait in Illy and ran into an irritating problem that I´ve yet managed to solve. I have my face, and then a semitransparent shape on top acting like a shadow, if I cut this piece into two with the knife tool, I get a strange line appearing at the cut. The pieces should fit perfectly, and I´m sure they do.

I guess the line is some kind of artifact that´s not really there, since it doesnt get any bigger if I zoom in on it, but it keeps appearing even if I make a pdf or jpg of the image.

Anyone knows what I can do about this? Or some workaraound.

I cant just make the cut off part overlap the bigger shadow, since it uses transparency and it would add up. What can I do?

[Scott Weichert]

Originally Posted by Devotee

since it uses transparency and it would add up.

That's what is happening due to anti-aliasing.

You can turn off anti-aliasing in the preferences and see if the line goes away.

In most cases, this is an AI on screen thing and that line is rarely visible upon printing or exporting.

You could simply use a solid shape, no transparency, that is a darker color. THat will eliminate the additive nature of the transparent objects.

[Devotee]

Thanks for the tip, but turning off anti-aliasing made it even more obvious *sigh* Also, its not a Illy-only artifact for me, it makes it to export (tiff, pdf, jpg), although I havent tried printing it (no printer avalible here).

I dont think I can just make it solid colour, since it´s a shadow that overlaps several other shapes with different colours, I would have to make and remake shitloads of shapes to fix those.

Uhmm, actually, is there a way I can pick the colour that is showing on screen when my objects have a transparency or blending mode? I dont seem to get the colour that is actually appearing, rather the 100% normal version of that colour.

[Lukas Engqvist]

I know I saw a screen dump but didn't see the gap.
I'd be very interesed in seing it. Also like to know what colours and blend mode.
There are some colours that will give a line since screen is RGB, for example a Red shape with a blue shape will appear to have a lighter colour stroke between the two.

It is very hard to comment without seeing the artifacts (and personally think it is a great project and would love to see it since I like seeing any pictures done with hard work).
I have not used the knife tool, but cane see that there is a risk of rounding off as you split a path. You are sure none of the objects has a stroke?

Interesting that the knife does not have any preferences as to tolerance or fidelity.
Had two shapes on top of each other cut with the knife and this is what i get:

So perhapps you should use some other tool to create the devide? Don't know how to set the resolution of the knife.

[Devotee]

Strange that you cant see the gap, I can see it on the picture I added, although its very small and in a slightly different shade than the rest of the shadow. Look closely about 1cm into the shadow from the left side. I guess I see it so clearly just because I know its there.

The shadow is made up of a filled shape, using a reddish black colour (280F00), set to 27% normal blending. I have tried changing the opacity to 100, also setting blending to multiply - doesnt matter. I also just now tried to split the shape using pathfinder divide command, same effect :/ Gets on my nerves

Here is the effect I´m after, you can see the full image I´m working on (although its not finished, still got some work to do). The shadow on the forehead is suppose to fade out, but remain a hard shadow on the rest of the face. I cut two slices from the left of the shadow in the forhead and used blend to make it fade out, I like the effect, but I get these artifacts where I cut no matter how I do.

Click the thumbnail

[Lukas Engqvist]

When you cut you only have the actual shadow selected right?
(I do see the darker hairline).

An opacity mask works much the same as a layer mask in Photoshop. You can use a mesh in black and white to create your mask. Using the opacity mask means you can work with opaque objects to create transparent effects, such as fading or feathering.

[Devotee]

Yes, only the shadow.

Hmm, I´m not at my own computor right now so I cant try it out, are you telling me that opacity masks can have a fading effect, and not just be hard shapes? If thats true, I didnt know that, and you solved many of my problems...

I´m not sure how I should do though, can you give a more detailed description, or link to a tutorial?

_______
edit.
I realised now that you where talking about OPACITY masks, ghaa...I for some reason thought you meant clipping masks. I havent even started experimenting with opacity masks yet, I did find some useful tutorials on it on bitbox now though, and it seems that opacity masks might be the cure for a lot of my problems!

[Lukas Engqvist]

The opacity mask can be made up of vectors or placed bitmaps, even in colour, but it is the lightness value that decides the opactity of the masked image to be revealed. It is probably one of the most powerfull and most advanced features of illustrator. (Before CS4 it was also the only way to blend to transparent)

This is a simple example I made:

starting with a simplified face ;P


selected the shadow (a transparent gradient set to 38% and multiply) and then
created an Opacity mask.


The transparency is controlled with the opacity mask (in my case a gradient mesh iin black and white, but when doing the mask you are not limited to just one object) I can choose to edit the mask or the object by using the opactity pannel. While editing the mask I can't edit any other part of the image.

[Lukas Engqvist]

You can't do this any other way (just added some colour light in the gradient)


But your portrait was more realistic

[Devotee]

OMG, thanks a bunch, I can see this is a really powerful tool. It will make my shading so much easier. I fixed my image, the shadow looks great now. I got confused at first because the effect was really strange, but I had the "clip" box checked, I guess this makes the mask into a clipping mask ASWELL? How does that work?

I also didnt see how I could change my mask later on, as it doesnt show up in the layers palette. But after your description I found out that if I click the opacity setting, I can change between two thumbnails representing both the mask and the masked object. THANKS.

I used a gradient mesh with black and white for the opacity mask, had to set it to 0% opacity at first so I could see through it to my artwork, but It worked really well.