You can also dup the base layer, and decompose to B&W using channel mixer.
I would put the green contribution to 1.00 and remove red and blue until
you get a good mask that isolates the "mortar" (you can use "preserve
luminosity").  That is, the 'mortar' is all white, while most of the bricks
are all black.

Then duplicate the base layer again, add a layer mask, and copy/paste the
B&W layer as the mask.  This isolates the mortar.  You can use "colorize"
to adjust the hue/sat/lightness of the mortar then.

It sounds complicated.  It's not, but you'll need to be comfortable with
these operations to use it.  So I did it already:

Just use "Colors -> Colorize" on the top layer to get the colors you want.

On Sun, Apr 24, 2016 at 11:01 AM Akkana Peck <> wrote:

> SArtino writes:
> > I suggested painting the wood edges to a bright
> > green because we make no blend that contains green, sowe can use a
> single photo
> > of one brick wall, and change the color of the green mortar joint to
> whatever.
> > 1 photo of each wall blend, edit 20 different mortar colors. Sounds like
> a
> > simple idea right?
> > *
> This was a week ago so it may be moot by now, but since I didn't see
> any other replies: one thing you can try is different settings of
> Select by: in the Tool options for Select by Color. You could try
> either Hue (since the mortar is greener than everything else),
> Saturation (since the brick color isn't saturated but the mortar is)
> or Green. Don't forget that Select by Color lets you drag to adjust
> how much is selected: up/left to select less, down/right to select
> more. It looks to me like with that image, Green isn't working at
> all but Hue and Saturation both work a lot better than the default
> of Composite.
> You'll still need to clean up your selection after making it,
> either by copying it to a layer mask or by editing it in the
> quickmask. Use Levels to threshold it (Threshold handles only black
> and white so you get hard edges; adjusting the middle slider in
> Levels usually gives a better result, with gradual edges). You
> might also want to use Dilate, Erode and Blur, and maybe paint
> over a few areas that didn't work out quite right.
> Good luck!
>         ...Akkana
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