cs3 masking similar pixels

[Koper]

so how can i go about masking pixels that are the same in two different photos. I want to extract light streaks from a photo and have an exact same copy of the photo without light streaks.

 

maybe a script that select the exact same pixels from two photos??

[AJLynn]

Make a layer mask and copy it?

[Koper]

sorry for being un-clear

 

I'm looking for some way in cs3 to auto select similar pixels... automatically but across 2 different photos (layers). once the selection has been done, then i can create the mask.

maybe I'm still unclear?

[mattclinch]

i'd be very interested in this too.

i know a difference layer of the two images will bring up similar pixels as near black, but the differences the other pixels (which is usually highly useless).

 

you need a layer style that keeps pixels within a certain tolerance of each other as black, but anything over a certain tolerance is white (or a shade of grey depending on the amount of variation in pixel hue/saturation/lightness to allow for aliasing and motion blur).

 

i hope there is a way of doing this.

[Koper]

smart, I like the way your thinking, i'll play a bit tommorow with it.

 

but maybe there is away to reverse engineer this tut

 

http://www.aecbytes.com/tipsandtricks/2008/issue27-photoshop.html

[mattclinch]

yea, i had a big play with image stacks, but again, the stack modes other than 'median' (for removing people and noise) all seem highly pointless to me (im sure some people will benefit from seeing the 'mode' pixel colour, but it eludes me who!).

 

i'll have a play around with it tonight and see if there is a way around this.

[Fooch]

Try this. It might not work as well (I'm just guessing via the math)

 

Put the streak layer on top of the clean layer.

Set streak layer as difference (in blend mode)

This will give the streaks as an inverted colour with most of the background being black.

 

CRTL + ALT + C and paste the combined layer (copy merged) to get the merged image (you can merge it as well but i like to keep a copy for backup)

 

The merged layer has black on most of it. You might have to crank the levels on it, or/and mask out the other black parts.

Set it then to linear dodge / colour dodge over the unstreak image to test. You should have the "streaked" image perfectly.

 

Alternatively, if all you need is car lines.. paint a black layer - draw quick lines via the pen tool and stroke w path .. set layer to colour dodge. Control light streaks intensity with fill not opacity