Photo Compositing - - Don't feather selections

Ed_L · #1 05-20-2002, 08:47 AM

When you make a selection, don't feather it. Save it as an alpha channel. From there you can dulicate the alpha channel, then run it through blur, blur more, or gaussian blur for a softer edge. Don't delete the original alpha channel in case you want to modify it further. The selection can be edited as many times as you want, and re-making the selection is not necessary.

Ed

Roger Roberts · #2 05-20-2002, 06:49 PM

Thanks Ed,sounds like a great tip. I'll have to start trying that.

Roger

DannyRaphael · #3 05-31-2002, 11:50 AM

A variation on this theme utilizes Quick Mask mode.

First make a hard edged selection using whatever method works for you, e.g., Lasso tool, Polygon select tool, Quick Mask, pen tool, whatever.

As Ed suggested it's a good idea at this point to save your selection via SELECT=>SAVE SELECTION, just in case you need to start over. Suppose you're selecting a building; you could name your selection "Select Building."

If you're not already in Quick Mask mode, use the keyboard shortcut "Q" to invoke it or click the 'Edit in Quick Mask mode' icon on the Tools palette.

While you're at it... double-click the 'Edit in Quick Mask mode' icon to display the options dialog box. Set the Quick Mask opacity to 100%; click OK.

Now invoke the BLUR=>GAUSSIAN BLUR filter, which will be used to "soften" (feather) the edges of the selection. Adjust the Radius slider until the desired amount of softening is achieved; then click OK.

Notice as you move the radius slider one way or the other you can "see" the effect on the selection. Having Quick Mask opacity set to 100% allows you to clearly identify which areas of the selection are "fully selected" (opaque) and which aren't. If the opacity is set lower, it makes it more difficult to visually assess the degree of feathering. At 100%, "What you see is what you get."

Exit Quick Mask (hit "Q" again or click the 'Edit in Standard mode' icon on the Tools palette).

Lastly... unless this is a trivial situation it may not be a bad idea to save this modified selection via SELECT=>SAVE SELECTION, using a different name, e.g., "Select Building - soft edges".

FAQ: Will this method yield the same results as SELECT=>FEATHER?

Yep, with the advantage of being able to "see" in advance the effect of adjusting the radius value.

Nick Moss · #4 05-31-2002, 01:56 PM

I would guess that the feathering process only affects the edge of the selection while the Gaussian blur will affect the entire selected area? If so, how can the results be equivalent? Oh, hold it, has this got something to do with the radius slider? (If it's like Photopaint it will adjust the number of pixels incorporated into the blurring algorithm)
NMoss

DannyRaphael · #5 05-31-2002, 03:20 PM

Hi Nick:

Thanks for your post. You raise valid questions.

I don't know enough about the "under the covers" implemention of blurring (Gaussian or otherwise) to even remotely claim I understand "why this works" from a technical perspective. Here's my intuative take... and I encourage rebuttal, further questioning, technical clarification and/or correction from you or anyone else so inclined.

For the sake of illustration let's assume we have 5"-diameter, circular, hard edged selection created at 100% opacity and we want to implement a 10 pixel "feather."

It's my understanding that various flavors and degrees of blurring are achieved by applying mathematical formulas/functions to the values of pixels within a sample area governed by radius.

At the center of our circular all pixels within a 10 pixel radius (20 pixel diameter) sample area would have the same values (100% opaque), so calculating differences among them them would result in "no change."

Apparently blurring algorithms take pixels 'beyond the selection boundry' into consideration, which would account for more transparency (feathering) at the edges.

Thanks for giving me the opportunity to stir the braincells. I hope I got this semi-correct.

~DannyR~

Ed_L · #6 05-31-2002, 04:31 PM

I think Danny is right on this. If you apply a blur to a mask, it only affects the edges of the mask, thereby giving the same results as feathering a selection by the same amount as applying in a gaussian blur.

Ed

Nick Moss · #7 06-01-2002, 01:59 PM

OK, I'll have to think some more. After your post I tried this with Photopaint 10 as I was puzzled by the idea of the blur staying at the edges of a selected area. I know nothing about Photoshop except that layers are a big deal (BTW is a layer equivalent to an object in Photopaint?). When I feather a mask only the edges are fuzzed up. I can select the feathering to be inside, outside, middle, or average with respect to the mask edge, and also in a linear or curved shape around the mask so it's pretty flexible. Also, you can see the effect before applying it as the unmasked area of the entire image can be pinked out, showing the degree of feathering around the masked area. Anyway, Gaussian blur of a selected area applies a uniform blur to the whole area, no matter what pixel radius is set. I suspect that this is a difference between Photoshop and Photopaint.

NMoss

Ed_L · #8 06-01-2002, 02:04 PM

I know absolutely nothing about Photopaint, and only slightly more about Photoshop

Maybe someone else can shed some light on this.

Ed

DannyRaphael · #9 06-01-2002, 02:25 PM

Even though I have both applications, I, too, plead a large 5th ammendment on PhotoPaint vs. PS.

I found a couple links where this technique is described from a PS perspective by others more knowledgeable than me:
Link 1
Link 2 - Ben Willmore PDF

It appears that it is indeed the difference in the respective implementations of these functions.

Viva la difference! Both applications have their strengths, weaknessess and quirks.

Nick Moss · #10 06-02-2002, 08:30 AM

Danny,
That's very interesting, the links you found settle it. The "quick mask" mode in PS is the key. I certainly don't want to get into a PS vs. PP discussion as they both do the job, like MSWord and Wordperfect both function to the same end. However, ... I think describing the peculiarities of Photopaint as "quirks" is very generous. All PP users are holdng their breath to see if Corel fixes it in version 11, (or even if there is going to be a version 11).
The reasons we settle on the programs we use often entails a circuitous process that has little relevance to the actual merits of the prgrams themselves. I have actually tried PS briefly and it was a very unsettling experience. I felt completely lost.

NMoss