[spxxxx]

Found this in my archives for tips etc - thought I would share it - the effort involved really does pay dividends for that special shot

1 Open your image that you wish to colour correct, and set the levels if necessary.
2 Open up the Curves Adjustment pallette and double click on the Black Eye-dropper. Set the r/g/b numbers to 10 in each box.
3 Double click the White Eye-dropper and set the r/g/b numbers to 245
4. Close the Curves box and click Yes when prompted to Save the new settings as default (You only have to do this bit once)
5. Open a new Threshold Adjustment Layer from the Layers window or via the menu. The image will temporarily change to all black and all white.
6. Move the slider to the extreme left, so that the Threshold level number gets down to 1. If you image does not have any pixels at that low level, you may need to go back up to level three or four or even more. You will be able to see the pixels at these values in the image window.
7. When you have found the lowest number pixel, you need to hover your cursor over the image window. You will notice that it changes to an Eye-dropper again. Go to a pixel that has the lowest setting and holding down the shift key click on this black pixel.
8 Now, do the same at the other end of the threshold scale, shift-clicking on the whitest pixel. Close the threshold dialog box and delete these new Adjustment layers that you have created.
9 Now, you need to create a new layer, which is 50 % grey, in order to set the grey-est point. So, use the new layer button on the layers window or Shift-Command/Control-N. Then, fill this with 50% grey. I use Shift-fn-F5 on my PowerBook, so I suspect that Shift-F5 will do it on a desktop. The fill contents needs to be set to the 50% grey.
10 Change the layer blending mode to "Difference" using the drop down control on the layer window. You will now see the image has changed again - temporarily.
11 Add a Threshold layer to this one, as you did before, and slide the slider down to the extreme left. This will then show you the pixels that are the grey-est. Once again, Shift click the Eye-dropper cursor on this pixel.

Nearly there, now

12 Close the dialog again and delete all these new layers, which will leave you with your original image and three "target" points, numbered 1,2,3
13 Open a new Curves Adjustment layer.
14 With the CAPS Lock key depressed click on the Black Eye-dropper in the Curves adjustment box and hover your cursor over point 1 in your image. When it is exactly in register, click on it. Do the same for the white point, number 2 and the grey point number 3.
15 Close the dialog box.

Your image will now have the black, white and grey points set to their blackest, whitest and greyest and any colour cast should have disappeared.

This may look long winded, but, after a couple of goes, it becomes very quick and easy. Y

[Dave]

Interesting tutorial. If you use a 3rd party for printing, they should be able to tell you the the absolute white & black points figures, so that you get the perfect print each time, using your method above

[spxxxx]

Hadn't thought of that .......... good point

Now if you were really clever you could create an adjustable action.........

[P-E]

Nice one I will have to give this a try TFS.

[spxxxx]

Right - idle hands and all that ........

I've written two actions which do most of the work for you which I have emailed to Steve

Instructions

1. Open picture
2. Run "1st part" action
3. This give you 4 layers
4. Make only the "background" and "black and white" layer visible
5. Double click on the threshold box for that layer - move slider left and "shift click" move slider right and "shift click"
6. Hide that layer and make the other 3 visible
7. Double click on the threshold layer and "shift click" - no need to move slider
8 Run "2nd part" action
9 Double click on curves adjustment box
10.With the CAPS Lock key depressed click on the Black Eye-dropper in the Curves adjustment box and hover your cursor over point 1 in your image. When it is exactly in register, click on it. Do the same for the white point, number 2 and the grey point number 3

Job Done

Simon

[Steve]

Thanks Spxxxx for the file.

Action file now available

Rep points given

[P-E]

I'm stuck between instructions 6 & 7

[spxxxx]

If you click on the eyes you make layers visable or not

The grey curves slider doesn't have to be moved (unlike what you did for black and white) as its already set to the correct shade.

Then just select a visable pixel and "shift click" to select your third point.

Simon

[spxxxx]

When you have made the bottom three visable you then click on the threshold layer second from top - not the original one you used for black / white

Simon

[P-E]

Cheers Simon

One other thing....when I've finished how do I delete the colour points on the image?

[spxxxx]

Originally Posted by P-E

Cheers Simon

One other thing....when I've finished how do I delete the colour points on the image?

Once you have clicked on all three points and clicked "ok" on the curves box they disappear and don't show on the now visable background layer.

Simon