Selecting fuzzy edge by color?

Selecting fuzzy edge by color?

Post by surface » Wed, 23 Feb 2011 04:28:22



I am very new at photoshop and I am trying to learn how to select an
object that has fuzzy edges against a background whose color varies
but is distinguishable from the object.  Think of a fern bush (mostly
green and brown stems) against  a background that is a reddish wall of
a barn.  Some of my more experienced photoshop friends tell me to just
carefully trace out each leaf and stalk, which is way too time
consuming.  I can test the colors of the pixels near the edges and I
see that the red compononent makes a marked jump from the object to
the background, and, I believe their must be some algorithmic method
whereby I could designate a matrix of colors that constitute the
background (or inversely, the object), and then I should be able to
move a small circle around the visible edges and let the program
figure out which pixels fall either within the object or within the
background based on the color limits I specify.

I want to believe photoshop already has this feature available, but,
the learning curve is immense, so, if anyone can jumpstart me please
advise.

 
 
 

Selecting fuzzy edge by color?

Post by Ragna » Wed, 23 Feb 2011 19:02:17



Quote:>I am very new at photoshop and I am trying to learn how to select an
> object that has fuzzy edges against a background whose color varies
> but is distinguishable from the object.  Think of a fern bush (mostly
> green and brown stems) against  a background that is a reddish wall of
> a barn.  Some of my more experienced photoshop friends tell me to just
> carefully trace out each leaf and stalk, which is way too time
> consuming.  I can test the colors of the pixels near the edges and I
> see that the red compononent makes a marked jump from the object to
> the background, and, I believe their must be some algorithmic method
> whereby I could designate a matrix of colors that constitute the
> background (or inversely, the object), and then I should be able to
> move a small circle around the visible edges and let the program
> figure out which pixels fall either within the object or within the
> background based on the color limits I specify.

> I want to believe photoshop already has this feature available, but,
> the learning curve is immense, so, if anyone can jumpstart me please
> advise.

You have already spotted that the red channel shows better contrast at the
edge than the other channels. SO . . .  copy the red channel into a new
alpha channel and edit its Threshold until the edges of the object show up
clearly. Tidy up the rest of the now black-and-white image and CTRL-click
the channel to create the selection you need.  You may need to have several
go's at it to get the result you want.
Hope this works. Undoubtedly others will suggest a less 'quick-and-dirty'
way of doing what you want.
R.

 
 
 

1. Q: Fuzzy Select

Hello,

could somebody explain me how fuzzy selection (for example in gimp)
works?

I know that there is a reference color (in rgb) and a tolerance value
from 0 to 255 (where 0 is no tolerance and 255 are all colors). But what
algorithm is used to calculate if a color matches this range?

Maybe some links or books for this topic?

Thanks in advance.
Kind regards
Eike Hoffmann

P.S. I want to use it for blue screening (similar to chroma key???)

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