Setting Image Black and White Points
Photoshop CS3 Tutorial
How to Set Image Black and White Points in Photoshop
The black and white pixel values should not be at the extreme ends of the luminosity values. By setting the darkest pixels in the image to RGB 10,10,10 you retain shadow detail.
The lightest pixels should be set to 245,245,245. In addition to making sure you don't loose your highlight detail, it also begins to correct any major color shifts in the image.
Open an image in Photoshop (File > Open...).
Add a Levels adjustment layer by clicking the Create Adjustment Layer icon and selecting Levels.
Double-click the Black Eyedropper and set the RGB values to 10,10,10. Press OK.
Double-click the White Eyedropper and set the RGB values to 245,245,245. Press OK.
Select the Black Eyedropper tool, hold down the Opt (PC-Alt) key and move the Black slider to find the darkest pixels in the image.
Click the darkest point in the image with the Black Eyedropper tool. It is now set to 10,10,10.
Repeat the process while holding the Opt (PC-Alt) key and moving the White slider to find the lightest pixels. Avoid specular highlights. Click the lightest pixels with the White Eyedropper. White is now set to 245,245,245. Click OK.