Color Correction
Below is copied and pasted from a forum entry at OPR. I use a modified version of this technique on nearly every restoration as my first step. The technique below is better. To see the forum discussion that follows, here is the link to Glenna's tutorial at OPR....
THE MOST PRECISE COLOR CORRECTION METHOD I'VE DISCOVERED!
1. In Photoshop go to Image/Adjustments/Curves. On the top menu bar, set your Sample Size to 3px by 3px. This prevents you from clicking on a "maverick" pixel that will throw off your correction, as is possible using the 1px by 1px.
2. Double click on each eyedropper and set the RGB values as follows:
These values will prevent your getting shadows with obliterated details and your highlights from being blown-out.
3. When you save the dialog box, Photoshop will ask whether you want to keep the values as defaults. Say yes.
4. Duplicate the original image layer.
5. Create a threshold adjustment layer above the dupe.
6. Use the threshold slider to find your highlight and shadow points: For highlights, move the slider to the far right. Then slowly move it left until you begin to see white areas. Use the preview toggle to ensure that you're setting your point on the actual image and not on damage. You can use the up and down arrows to have finer control over the movement of the slider (Up= 1 number higher ; Down=1 number lower). Shift/click on the area that appears to be the "whitest", and a small cross-haired circle with the number 1 below it will appear.
7. Without leaving the threshold dialogue box, shift the slider to the far left and begin slowly moving it to the right until black areas appear. Follow the same guidelines as for setting the white point, shift-click, and you'll see a small cross-haired circle with the number 2 below it.
8. Close the threshold dialog box. The markers will disappear, but they'll show up again later. Discard the threshold adjustment layer.
9. To set your mid-tone (gamma), create a new layer above the dupe layer and fill it with 50% gray. Set the gray layer to the Difference blend mode. The image will look VERY strange. Above the gray layer, create another threshold adjustment layer. Move the slider to the left until you see white areas. Choose the smallest white area that is part of the image, rather than damage (shift-click). A small cross-haired circle with the number 3 below it will appear. Often the gamma point will coincide with either the white or the black point. If so, just remember which it is.
10. Close the threshold dialogue box and discard the threshold and gray layers.
11. Go back to your curves dialog box. The set points will reappear on your image. Choose the white-point eyedropper and click it in the exact center of the cross hairs of your number 1 circle. Choose the black-point dropper and click in the center of the number 2 circle. For the mid-tones use either the number 3 circle or the 1 or 2 that coincided with the gamma point. By using your shift lock, you can see targets that are identical to those you set. When one is on top of the other you won't see a target, so you'll know you're directly over it.
If you toggle between the original and adjusted duplicate layer, you'll be amazed.
Note: This won't always give you perfect color correction, but I've found that it's a great starting point, and usually any further adjustments you make will be minor. The beauty of this method is that there's no guessing. You set your numbers, set your points, and as long as you're on a part of the image that's relatively pristine you'll get phenomenal results.
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