anti-aliasing vs. feathering

M
Posted By
MathDreamer
Apr 11, 2004
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2326
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I believe anti-aliasing makes an edge look smoother by making the pixels fade out to tranparency from an edge.

Feathering blurs the pixels.

1) What is actually happening to the pixels?
What are the similarities and differences between anti-aliasing and feathering? I understand visually the difference. But how are the pixels changed?

2) Also, does using the gaussian blur have the same effect as feathering? I’m asking this because I read a method that lets you see how much feathering is being applied by using the gaussian blur. I want to know if there is a difference in how the pixels are treated.

The method is as follows:
Step 1: Make a selection
Step 2: Change to quick mask mode
Step 3: Use the gaussian blur filter, which effects the selection and not the image. You see the blur on the edge of the selection.
Step 4: Get out of quick mask mode.
Step 5: Do whatever it is that you need to do with the selection.

Sincerely,

Robert Dawson
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anti-aliasing feather vs

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S
stuff-it
Apr 11, 2004
On Sun, 11 Apr 2004 05:37:58 -0700, wrote:

I believe anti-aliasing makes an edge look smoother by making the pixels fade out to tranparency from an edge.

Feathering blurs the pixels.

1) What is actually happening to the pixels?
What are the similarities and differences between anti-aliasing and feathering? I understand visually the difference. But how are the pixels changed?
2) Also, does using the gaussian blur have the same effect as feathering? I’m asking this because I read a method that lets you see how much feathering is being applied by using the gaussian blur. I want to know if there is a difference in how the pixels are treated.

The method is as follows:
Step 1: Make a selection
Step 2: Change to quick mask mode
Step 3: Use the gaussian blur filter, which effects the selection and not the image. You see the blur on the edge of the selection.
Step 4: Get out of quick mask mode.
Step 5: Do whatever it is that you need to do with the selection.
Sincerely,

Robert Dawson

Feathering uses transparency. For example, If you take two layers, white on top, black on bottom. Apply a mask to the white and use the marquee selection , round or sqare, doesnt matter. No feathering. Hit the delete key and u got a perfect sharp edged cookie cutter hole where the black will show through.

Now take the take the lection again and apply as much feathering as you like, say 50 pixels. you will then see it will taper off into gray.

so lets say a round selection with no feather would be a perfect punch hole.. a feather of say 50 will reach outside the outer edge 50 pixels and use graduated transparency. That is exactly how to create a vignette.

antialiasing is just pretty much blurring hard squared blocks to give it more of a rounded shape for text and graphics mostly so things dont look so blocky…

Two totally diffrent animals.. Hope this makes sense to ya.. look at a vignette of how it gradually fades,
CW
Colin_Walls
Apr 11, 2004
On (2):

I understand that applying GB to a mask is exactly equivalent to feathering. However, it is much, much more flexible and, as you observe, visible. Personally, I tend to use layer masks, not QuickMask, but the effect is the same. The only difference is that you can return to a layer mask and change it later.

Broadly, masking and selection are equivalent and interchangeable. I usually do a rough selection [using whatever tool does the job] and then add a mask, which picks up the selection automatically, and carry on from there.
CW
Colin_Walls
Apr 11, 2004
As another contributor to this forum often points out, accuarate selection is the key to getting the best from PS. I would simply add that masking is a better way to achieve the same result.
DM
Don_McCahill
Apr 11, 2004
A bit about AA and feathering. AA only works on slanted or curved items, and will use differing amounts of pixel density to make these look smoother, and avoid the stair-step effect. If you apply AA to a square, nothing will happen. If you move the square a half pixel, then it might, and if you rotate it any amount (other than a multiple of 90 degrees) it will also coming into effect.
RW
Rene_Walling
Apr 11, 2004
I believe anti-aliasing makes an edge look smoother by making the pixels fade out to tranparency from an edge.

The pixels can also fade from one colour to another

Feathering blurs the pixels

Feathering does NOT blur your image pixels, feathering blurs the edges of your selection. Or to put it another way, feathering blurs the selection mask (not the image).
M
MathDreamer
Apr 12, 2004
Thank you for your help everybody

The pixels can also fade from one color to another, but I believe this happens by fading out to tranparency from an edge. The outer color becomes more prominent because the pixels on the outer edge have more transparency, which shows the outer color. I believe this is what Photoshop is doing to the pixels.

I have a follow up question.

I made a mistake when I said feathering blurs the image pixels, which implies all of the image pixels are effected. As Rene pointed out it blurs the edges. But what is Photoshop doing when it "blurs" the edges? What is it doing to the transparency of the pixels? What else is going on?

Sincerely,

Rob
DM
Don_McCahill
Apr 12, 2004
I don’t think it is doing anything else. If you have a feather of 10 then the pixels are selected at 5, 10, 15, 20, etc opacity to what works out to 10 pixels on the outside of the old selection at less than 50 percent, and 10 pixels on the inside of the old selection from 50% to 100%.

It is not touching the pixels of the image at all, only of the selection … when you delete or do something else, then the percentage of opacity comes into play.
L
LenHewitt
Apr 12, 2004
Rob,

A selection is just a mask. A feathered selection is a soft-edged mask.

To see that, just save the selection to an alpha channel and then view that channel. (Or hit Quick Mask)

As Don says, nothing happens to any image pixels until you USE that mask

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