In 8 bit, add an adjustment layer called "Threshold". Move the slider back and forth and it will show those areas. This is in PS7.
Gary
In levels dialog>option – click the highlight and/or shadow sliders. Your image will show what you want.
Thanks both Gary and Barry for the tips.
Have a nice Xmas
Mario
One more thing on Gary’s suggestion. After you do the threshold, pick the color sampler tool and number the darkest then lightest areas. Then trash the threshold adjustmaent layer and you have the darkest and lightest areas of your work. Also, in levels, hold down the alt key while sliding the left and right slider inward just until the area shows the lightest and darkest area.
I’m sure are many other ways to do this.
Marion