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Finding the White or Black Point in Photoshop
Using Photoshop’s Levels dialog is a great way of adding a quick punch to your photos. Dragging the white and black point sliders in a little reduces the dynamic range and often improves the overall tone of a picture.
The Levels dialog is also very useful for color correction and is a great starting place to find good white and black point references.
With your Levels panel open, click on the white point eye dropper. You could just click on the image and set the white point from here, but holding down the alt key (it’s marked that way on my Mac keyboard too) posterizes the image, creating an easy way to see the differences in color ranges.

Use Levels to find the white or black points in your images
You can drag the sliders too… If you want to place an eyedropper to use for a reference point, hold the shift key down too and click on your image.
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