Monday, February 11, 2013

Using Photoshop Calculations To Make Selections and Hello Bozeman

Real quick, just to start the post I'd like to say hello to a reader in Bozeman Montana, USA.  I don't get a lot of readers from Montana in general, but for the past couple of months I've seen someone from Bozeman peeking in almost every day.  That kind of interest deserves some sort of recognition.  I do get consistent visitors from several cities from around the world, but usually they're larger cities.  There's Athens, Greece.  Athens is large enough that it could be a circle of visitors, each checking in once a week or once a month.  There probably isn't a day that goes by without someone from New York popping in, but that's just the fact that there's eight million people in NYC.  It could be 365 people stopping by once a year.  Bozeman has less than 40k people.  I'm guessing I don't have a real large following in Bozeman, so welcome (in the words of Sheldon Cooper) Bozite.  From the image on Wikipedia I'm guessing your city council thinks traffic signals are a status symbol.  You appear to have one signal every half block.  Enough about that.  Today's image comes from separating out the stalk of some sort weed by using Adobe Photoshop CS6 (and before for several versions) Calculations dialog box.  If you've clicked on Calculations (Image/Calculations), your next click was probably to hit the Cancel Button.  To find out why I use this monster dialog box and where to use it, hit the "Read More".

Calculations is not for the faint of heart and, unfortunately, not for users of Adobe Photoshop Elements (of any version).  PSE users don't have Calculations and don't have access to Channels.  (You have Channels, just not access to them.)  I'm pretty sure people's first question would be why I'd use Calculations rather than using the Quick Selection Tool (W) and Refine Edge.  Easy answer.  The Quick Selection Tool and Refine Edge work well (great sometimes) if you're selecting something with fuzzy, furry or flyaway edges.  Not so much if there are a lot of internal voids.  Directly in front of me as I wirte this post is an image of a shoreline up in Maine.  It has a white birch tree, a pine, and (what looks like) a maple tree.  The birch has very fine branches.  The pine has lots of individual small, needle covered limbs and the maple is full of holes between leaves.  It's a nightmare to try to work with as far as the QST and RE.  I've tried it.  I just can't get it to work worth a darn.

Calculations on the other hand, makes making the selection a snap.  Go to the Channels Panel.  Flip through the Red, Green and Blue Channels.  See which one gives the strongest initial contrast.  Leave the strongest Channels selected.  There's no reason to make a copy of the Channel.  Calculations is going to result in its own Alpha Channel.  Go to Image/Calculations.  The Channel you left selected should be pre-selected in the dialog box.  In the third internal box you'll see Blending.  Flip through the Bland Modes to see what mode gives the best  increase in contrast.  Once you determine the best contrast and have made sure the Result box is set to New Channel, click OK. 

You can now use a Levels Adjustment (Image/Adjustments/Levels) (don't use an Adjustment Layer.  Be sure to use a Levels Adjustment.  There's a difference.)  Bring both outside tick marks toward the center.  If there are any left over grey areas, paint them out using the Brush Tool (B) with either White or Black.

In order to use the Selection, click on the Alpha Channel while holding down the CTRL key.  That will load the Channel as a Selection.  Then click on the Add New Layer Mask icon at the bottom of the Layers Panel.  This will produce a Layer Mask with the Selection already masked out.   It's different from the Quick Selection Tool.  It should be used for a different reason.