What is going on with smart highlighting in Extract?

SG
Posted By
Scottie_G.
May 27, 2005
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748
Replies
12
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Closed
I understand the premise of smart highlighting (to be use for more defined edges), but wondering, what is going on behind the scenes that makes that a better extractions as opposed to using the usual soft thick brush. thanks.

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C
chrisjbirchall
May 27, 2005
Extract works best when you draw the narrowest possible highlighter whilst still fully covering the transition between foreground and background.

Clearly without smart highlighting a thicker brush makes the task easier. With smart highlighting on, however, not only are the edges easier to follow but the the program paints what it perceives to be the narrowest highlight possible.

You can speed up the process by toggling the plain brush into a smart one as you work by holding the Alt key.

Here’s a tip which works well if your background is quite plain, for instance a plain wall or a paper studio backdrop.

* Before going into Extract, click on the background with the magic wand to make a rough selection. * Invert the selection.
* Go Select>Modify>Border and set this to about 6 pixels * Invert the selection again.
* Save as an alpha channel
* Deselect the ‘marching ants’
* Open Extract
* Select this alpha channel in the Channel drop-down menu

You will now find your image has been "smart highlighted" without all the laborious work with the highlighter tool!

Before previewing the extraction check at a high magnification and go over any areas (such as hair) where the automatic highlighter needs thickening out to completely cover the transiton areas.

Hope this helps.

Chris.
SG
Scottie_G.
May 28, 2005
"With smart highlighting on, however, not only are the edges easier to follow but the the program paints what it perceives to be the narrowest highlight possible. "

thanks great reply chris:

why are edges easier to follow? seems edges are easier to paint with larger brush. what does that mean program paints with what perceives narrowest highlight possible. don’t seem to understand that.
C
chrisjbirchall
May 28, 2005
The Highlighter should paint over the transition, half of it covering the background and half covering the foreground.

When the plug-in computes the extraction it only "looks" within the highlighted area. A sharp, hard edge is easier to find. With a soft edge (such as a garment or something slightly out of focus) the plug-in needs more information to correctly determine what is background and what is foreground. Hence a wider highlight line will provide this information.

This is Extract’s strength. Other selection methods within Photoshop will generally draw a fine line between FG and BG. Extract will allow a transition between the two (Almost like "selectively feathering") giving a mare natural result on soft edges.

Extract also works well on fine hair. By brushing a wide highlighter over areas where the background can be seen "through" the hair, the plug-in will usually do an excellent job of separating it out.

Chris.
PC
Pierre_Courtejoie
May 28, 2005
Scottie, this is getting annoying!

Have you had the thought to try smart highlighting, before asking questions?

I have to say that I never used it before (thanks , Chris!!) but I did understand exactly what Chris said, after I tried it.

Try it on images with sharp edges, and soft ones. You’ll see it happen right in front of your eyes.
C
chrisjbirchall
May 28, 2005
Whilst on the subject of hair, let me tell you how to cope with the colour bleed which can occur when the background is a strong colour.

At our studio, for instance, we often use a blue or green chromakey background to make these cutouts easier. Unfortunately this will often leave tinges of green in the fine strands of hair around the edges.

To eliminate this, take your extracted image and click the "protect trasparency" button in the layers palette. Then you can use a soft clone tool set to the blending mode "Colour" to paint away the colour fringing by sampling the hair colour from a point a little way in from the affected areas.

Hope this is of some use.

Chris
SG
Scottie_G.
May 29, 2005
great info Chris, that provided some understanding on PHotoshop’s point of view I was looking for. Why not shoot on white? also, do you use the channels method of extraction? ie making your own high contrast mask? or just use extraction tool?
C
chrisjbirchall
May 29, 2005
Mornin’ Scottie

Why not shoot on white?

I do. and on black. Depends on the subject really. Unlike the movie industry "chromakeying" doesn’t always have to be done against Chromagreen or Chromablue.

It’s just that the Green background is quite handy if you need to make very quick selections – when working on a large number of images from the same shoot for instance. It is a colour which doesn’t often appear in a (portrait) subject.

The majority of my "keying" work is actually done against a mid tone grey. This is fairly easy to select and leaves no nasty fringing in the hair. With fine blond hair, however, we usually have to resort the the green.

do you use the channels method of extraction? ie making your own high contrast mask?

I use the Extract tool.

This actually works by making a channel mask.

Here’s a handy tip for when you want to extract the background from a 16 bit file (Extract only works in 8 bit):

* Make a duplicate of your file
* Convert the dupe to 8 bit.
* Run the Extract filter.
* Leaving this file open, go back to the 16 bit version
* Go Select>Load Selection
* In the drop-down boxes choose the Alpha channel from the Duplicate

This will load the alpha channel you created in the 8 bit image into your 16 bit version. Now you can convert this channel to a selection and hit delete to remove the background.

Chris.
PC
Pierre_Courtejoie
May 29, 2005
Also, some users prefer the "regular way" to create selections in Photoshop, then create a selection border, and import it in extract.

Why, will you wonder? because extract also does color edge decontamination. (this is why extract does not create a mask)
SG
Scottie_G.
May 30, 2005
I’m reading Katrin Eisenman’s great book on masking, and while there are all so many ways to extract, so many ways to use blending modes etc, it goes on and on–making your own masks…. I’m just wondering if you get good with Extract Filter, maybe you can bail on all those other ones. Is this sort of what you concluded, Chris?
PC
Pierre_Courtejoie
May 31, 2005
Scottie, if Extract was THE universal solution for masking/extracting, do you think that an acclaimed Photoshop Guru would have written a whole book about the different methods of masking?
Y
YrbkMgr
May 31, 2005
Scottie,

One of the keys to photoshop is learning different ways to isolate different elements. Each has its advantages and disadvantages, depending on image composition, intent, and a users skill or familiarity with the different ways to isolate image elements.

Consider: If I type text into an image, thus creating a text layer, why would I use the extract tool to select and thus isolate that element?

For some images it makes sense to start with the magic wand, for others, the Pen tool, and for others… well, the’re in the book. There is no "one size fits all" – unless one chooses to limit ones skill with photohsop, that is.
SG
Scottie_G.
May 31, 2005
thanks.

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