Graphics Tips

Photoshop Quick Tip #1: Use Threshold to find an image's darkest and lightest areas

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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.