Apr 27 2009
Photoshop Quick Tip 1– Use Threshold to find an image’s darkest and lightest areas
Often when color correcting, you need to know the darkest and lightest parts
of an image are. Most of the time you can eyeball it or designate the spots
you want to be the lightest and darkest. But for those times when your
eyes may deceive you or you want to be more precise, this simple trick will
do the job.
With the image open in Photoshop, go to the Image menu and choose the Adjustments
submenu and then select Threshold…
When the Threshold window comes up it will immediately preview its influence
on your image–don’t worry, we won’t actually be applying the effect, we’re
just going to use its preview to highlight the shadows…and the highlights.
You’ll see.
Drag the slider far to the left until almost all the black disappears. The
black represents the darkest areas and when you drag the slider to the left
you force Photoshop to cut off all but the darkest shadows. By dragging the
slider until one more click to the left will remove all the black pixels, you
have effectively revealed the image’s darkest point (see red arrow below).
Do not click OK or Cancel yet, but hold down the Shift key and click on one
of the remaining black areas in your image. You have now placed a Color Sampler
point on the image that will be viewable when you select the Eyedropper tool
or an adjustment filter and will be monitored in the Info palette.
Now, with the Threshold window still open, drag the slider far to the right
until almost all the white disappears. As you may have guessed the white represents
the lightest areas. Dragging the slider to the right like this forces Photoshop
to cut off all but the brightest highlights. Similar to you did with the shadows,
if you dragged the slider until one more click to the right would leave you
with an entirely black image, you have effectively revealed the image’s lightest
point.
Shift-click one of these remaining white pixels to drop a Color Sampler point
that will mark the image’s highlight. Notice in the image below (look carefully)
how the red arrows show where the original Color Sampler point has remained
and where the new one has been placed.
You may now Cancel the Threshold effect. Now choose the Eyedropper tool in
the Tools palette and, sure enough, your Color Sampler points will reappear.
Open the Info palette and it will show you the color value below each of these
Samplers. As you run filters and adjustments the values in the Info palette
will change along with the image to reflect the changes you have made. To remove
a Color Sampler point, choose the Eyedropper tool and move the cursor over the
point you wish to delete. Hold down the Shift and Option keys and your cursor
will change into a pair of scissors. Click the Color Sampler point and it will
be removed.