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bluemouse

free hand (lasso) tool and antialiasing

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Hello,

New user here. I'm trying to figure out how to get the freehand tool to create a smooth selection that isn't so jagged.

In the screenshot, the five cut outs (from left to right) are as follows:

5a845dee19761_2018-02-14screenshot001.png.b8251d970d6d1cfc14e5061ae5d6d12e.png

1. lasso, anti-alias OFF (very jagged)

2. lasso, anti-alias ON (less jagged, but still pretty bad)

3. lasso, anti-alias ON, Feather = 1px (blurry)

4. erase tool, hardness = 100 (better)

5. erase tool, hardness = 80 (to my eye, best)

I'd like the lasso tool to create selections that are closer to the erase tool example so I can fill them in with a color. I don't understand why even with the anti-alias on, the lasso selections are still really jagged.

The document shown is a drawing scanned at 600dpi, zoom 200%.

Any help would be most appreciated! Thank you!

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I've tried to make the freehand selection tool work better but it ain't doing it, so, what about a workaround?

  • Make a pixel layer
  • Fill it with black or white or any strong colour
  • drop its opacity to 50%
  • Use the eraser to draw the selection/s you want
  • then to create the selection press <Cmd> on Mac, <Ctrl> on Windows, and click on the pixel Layer
  • You should now have the marching ants selection.

Now you can hide the pixel Layer and do whatever you need to with the selection.

 

If you want to fill the selection area you will need to invert the Pixel selection <Cmd> + <Shift> + <I> Same on Windows but replace <Cmd> with <Ctrl>


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6 hours ago, bluemouse said:

I don't understand why even with the anti-alias on, the lasso selections are still really jagged.

What are the pixel dimensions of the file?

 

The anti-alias option only affects whether or not the pixels on the edges of the selection are opaque or are smoothed by applying transparency to them. IOW, it has an effective 1 pixel radius. Feathering reduces the sharpness of selection edges by partially selecting the edge pixels using a variable pixel radius, which can be a fractional number like 0.2 or 3.1 pixels.

 

Because both of these options are based on pixels, to get results more like the Erase tool, you will need to adjust the feathering radius proportionally to the pixel dimensions of the image. So for example, if your document is only a few hundred pixels wide or tall, a feather radius considerably less than 1 px may be what you need to use.


Affinity Photo 1.6.7 & Affinity Designer 1.6.1; macOS High Sierra 10.13.6 iMac (27-inch, Late 2012); 2.9GHz i5 CPU; NVIDIA GeForce GTX 660M; 8GB RAM
Affinity Photo 1.6.9.81 & Affinity Designer 1.6..2.24 for iPad; 6th Generation iPad 32 GB; Apple Pencil; iOS 12.0

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Thank you for responding firstdefence and R C-R! Much appreciated.

firstdefence, thanks for the workaround. I used your suggestion and it definitely did what I needed it to do.

R C-R, I had no idea you could set the feathering radius to partial pixels! It's not intuitively obvious to a new user like myself, and the UI doesn't make it clear because the slider used to change the radius only increments in full pixels. Thanks for pointing that out; I doubt I would've ever figured that out on my own. The file in question isn't that small - about 5000 x 3500 pixels, but shrinking the feathering radius to about 0.2 pixels smooths out the edges of the lasso selection.

Re: the freehand tool itself though, when I look at the marching ants, it looks like it only selects full pixels -- is that correct? Even though reducing the feathering radius to 0.2 pixels makes the edges smoother, the selection itself still seems more jagged than a similar shape created by the erase tool. I'm guessing the way the selection tool works limits how smooth a curve the freehand tool can create.

 

 

2018-02-17 screenshot 001.png

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12 hours ago, bluemouse said:

Re: the freehand tool itself though, when I look at the marching ants, it looks like it only selects full pixels -- is that correct? Even though reducing the feathering radius to 0.2 pixels makes the edges smoother, the selection itself still seems more jagged than a similar shape created by the erase tool. I'm guessing the way the selection tool works limits how smooth a curve the freehand tool can create.

 

A pixel selection's marching ants are always drawn on pixel boundaries and therefore appear stair-stepped if you zoom in sufficiently, regardless of the tool used to make the selection.

A given pixel can be partially selected (resulting in partial opacity when a mask is created from a selection, for example), as I'm sure you are aware. Marching ants enclose regions where each pixel is selected by at least 50%, and therefore the outermost pixels of a feathered selection will lie outside the marching ants.

Quick Mask mode provides several alternative visualisations of a pixel selection, and there you'll see the varying intensity of selection when a selection is feathered.

 

 

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12 hours ago, bluemouse said:

R C-R, I had no idea you could set the feathering radius to partial pixels! It's not intuitively obvious to a new user like myself, and the UI doesn't make it clear because the slider used to change the radius only increments in full pixels.

The slider will increment by fractional pixels if you hold down the Alt/Option key while adjusting it. Also, if you have a mouse with a scroll wheel, you can hover the mouse pointer over the numeric field value & use the scroll wheel to change it. Holding down Alt/Option changes it by 0.1 px increments & holding down the CMD key (probably Ctrl on Windows) increments it by 10 px. And you can even click & drag the mouse pointer left & right over the "Feather" text in the Context toolbar to change the value.

 

This also works for most other numeric fields in the UI.


Affinity Photo 1.6.7 & Affinity Designer 1.6.1; macOS High Sierra 10.13.6 iMac (27-inch, Late 2012); 2.9GHz i5 CPU; NVIDIA GeForce GTX 660M; 8GB RAM
Affinity Photo 1.6.9.81 & Affinity Designer 1.6..2.24 for iPad; 6th Generation iPad 32 GB; Apple Pencil; iOS 12.0

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