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Polygonal lasso tool creates squary lines, why?


Morzun

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(I think) I'm not a newbie anymore when it comes to Photoshop, but the thing that's happening now is beyond my knowledge.

Somehow, when I try to make triangles using the Polygonal Lasso tool, it converts the straight lines to squares.
Hoping someone knows why this is happening.

Here's how it looks after I made my selection: Untitled-2.png

Thanks in advance!
 

MrToM

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Any marquee is based on the pixels in the image.

As the image is essentially a grid of [usually] square pixels then the marquee has to follow the shape of the pixels.

Although Adobe likes to think you can split a pixel, you cannot.
A marquee can only contain 'whole' pixels.

The pixel is the smallest 'element' in a digital image.

Regards.
MrTom.
 

Morzun

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Thanks Tom.

I already thought it might have something to do with that.

So to work around this, I could simply make a bigger canvas and try my luck on there?
 

ALB68

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Thanks Tom.

I already thought it might have something to do with that.

So to work around this, I could simply make a bigger canvas and try my luck on there?

I don't think there is a "work around" for this nor would you need one. As Tom said more or less, this is just the way it works. Your zoomed in really high to display this.
 

Morzun

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Yeah, I was zoomed in a lot. I zoomed out less though, and yet the selections I make end up very ugly-looking.

In this tutorial, they seem to zoom in a good bit too, but it isn't happening to them.
 

MrToM

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Sort of...

No matter what you do you will always have that effect......it can't be anything else with a grid of squares...if you think about it, so in order to reduce the 'squareness' of the marquee you need more pixels to represent the same 'area' of the image.

The only way you can do that is to re-sample the image.

Whilst this will enable you to make a better marquee it does also mean that the area will contain pixels that were not in the original image....re-sampling 'adds' pixels to an image to make it bigger by taking one pixel at a time, looking at the surrounding pixels and adding more pixels around it based on those already there.

The 'added' pixels are calculated by any one of several 'algorithms' depending on what you want to do....make it bigger or smaller.

Re-sampling is classed as a big 'no no' and should be avoided at all costs.....the artist should ensure the image has enough pixels in it to work with beforehand.....unfortunately this is not always the way people do it and re-sampling is required.

My advice would be to make a copy of your PSD file and experiment with up-sampling......remember, increasing the pixel dimensions by 2 means the total pixel count increases by a factor 4.....each pixel in the image now will be replaced by 4 pixels.

Make the image 4 times bigger and your pixel count goes up by a factor of 16......this could lead to massive file-sizes so be careful how much you up-sample by......go up in small steps.

Check it each time to see if you have enough pixel 'density' to marquee the same area as before but with a smoother edge.

I doubt you'll get it to a point where you cannot see the individual pixels as the area you want to select is very small but you should get it somewhat better.

As far as I know there isn't anything else you could do to improve it.....there are only so many pixels in an image after all.

Regards.
MrTom.
 

Morzun

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Thanks guys, that's some good stuff to know.

My previous post apparently wasn't approved by a moderator (yet), but in there I basically linked to a tutorial in which a guy also zooms in and uses the exact same tool - only he ends up with perfectly straight lines.
I also just recalled this to be the first time ever I notice Photoshop doing this when using the polygonal lasso tool, so I'm still a little confused.
 

MrToM

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...in there I basically linked to a tutorial in which a guy also zooms in and uses the exact same tool - only he ends up with perfectly straight lines...

I thought the 5 post thing had been lifted but maybe not.
There are no links in any of the posts but if you could see your way to trying again I'd very much like to see that tutorial.

You may have to get your post count up to 5 before it will allow you to post links and whilst posting for the sole reason of upping your post count is frowned upon I'm sure in this case it will be ok.

Much appreciated.

Regards.
MrTom.
 

ALB68

Dear Departed Guru and PSG Staff Member
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I thought the 5 post thing had been lifted but maybe not.
There are no links in any of the posts but if you could see your way to trying again I'd very much like to see that tutorial.

You may have to get your post count up to 5 before it will allow you to post links and whilst posting for the sole reason of upping your post count is frowned upon I'm sure in this case it will be ok.

Much appreciated.

Regards.
MrTom.

I can't say , I didn't see the mod notice as it didn't appear on the post. Anyway I took care of it. Sorry for the inconvenience. The 5 post requirement for links has been negated but I don't know if the system knows it :banghead:
 

MrToM

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Yeah....if you look at that video you can see that he has LOTS more pixels in the image.

The image he is working on is 3840x5760px so his marquee area actually contains many, many, more pixels than your example.

If you download the Project Files for that tutorial and open up the image in PS, do the same marquee as the tutorial and zoom in so that you can see the pixels you'll find the exact same 'squared' boundary as in your example..

Remember, PS is a PIXEL based image editor......the PIXEL is THE most important thing in the image.....and everything that PS does relies on them.

One other thing to note is that things like the marquee boundary, (Marching Ants), and guide lines, your brush shape cursor etc etc are all Non-Scaling. That means that no matter how far you zoom into an image those things will not change their size...OK, the brush will but the line thickness of the cursor will remain constant.

These Non-Scaling elements are draw according to your SCREEN resolution and NOT part of the Image....so a 'guide line' is drawn using a single line of [ LCD monitor ] pixels and NOT a single line of IMAGE pixels.

Likewise all vector shapes are drawn using the screen pixels and are converted to image pixels when rasterised.
All the marquee tools also use the screen pixels until you finish the creation....this is why when you use the Polygon Lasso tool it draws nice straight diagonal lines....because its using the screen pixels, but when you close the shape the line jumps to being 'squared'.....because now its using the image pixels.

Get it? LOL.

Its not that easy to get your head around granted, but thats the basic jist of it anyways....just in case you wanted to know.

Regards.
MrTom.
 
Last edited:

Morzun

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That's something I never actually thought of myself, thanks Tom. I can already tell I'm going to visit this forum frequently.

,
 

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