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The End Game Setting End Points

In our rush to sell you into RAW shooting we sometimes forget that some of our photographers either cannot or choose not to shoot RAW. They are then left with having to correct images downstream, often without ready or obvious points of reference on which to judge and adjust colour. With the help of Adobe Evangelist, Julianne Kost, here we show you how to go about it.

Particularly when you have shot in mixed light or scanned negatives, you may end up with crossed curves. These occur as a result of the shadows carrying a cast in one direction and the highlights carrying a cast in another direction, eg green shadows and red highlights. In this situation global colour adjustments are of little help; you can’t run off to the Photoshop Filter menu and use a single correction filter as this will taint both highlights and shadows to an equal degree. You can visit the Color Balance dialogue box but there you are faced with three Tone Balance radio buttons and six colour options, a total of 18 ways to get things wrong, even if you are able to spot the subtle difference between a cyan cast and a blue cast (to say nothing of in-between, tertiary effects).

Pinning down the colours numerically is the way to deal with this problem and a combination of levels and curves adjustments is a good tactic to employ.

The basis of the method is simple. You look at the red, green and blue values using the Color Sampler tool. Using these values for reference you push two shadow values down to match the lowest RGB value of the trio, then two highlight values up to meet the greatest of the RGB trio. For the mid-tones, you bring the highest and lowest in towards the middle value.

The method is best explained by example and we have used the same image that Julianne Kost uses in her instructional DVD. Hers DVDs are published by software-cinema and are now available through the SWPP & BPPA, online book store.

1. Find the lightest and darkest portions of the image using the Threshold function [1]. In the composite screen grabs an Adjustment Layer has been made for Threshold. At A, on the left, the highlight is selected and marked with the Color Sampler after dragging the Threshold slider to the right. At B, on the right, the threshold has been pulled back across the graph to detect the deepest shadow and then marked with the Color Sampler tool. The mid-tone C we will talk about later.

2. Referring to the info palette [2], which now contains the additional data for the Color Sampler points, we find that the RGB values are as follows: Our aim, therefore, is to drop the shadow red and green values down to the 42 points of the blue and raise the green and blue highlight values up to meet the 237 value of the red channel. When the RGB values are equal the colour is a neutral. This is accomplished using levels.

3. Discard the Threshold Adjustment layer as its job is done.

4. Make an Adjustment Layer for Levels.

5. Highlight the red channel in Levels then highlight the left-hand, shadows Input Level data entry box.

6. Click on the up arrow key while watching the data in the Info Palette. Note that the numbers alongside the dropper number (eg #1) should change from 67/67 until you get to 67/42, the target point for this example. What this has done is to bring the red channel value down to meet the lowest of the trio.

7. Now highlight the green channel, then the shadow Input Level and arrow key up until the Info Palette data moves from 54/54 to 54/42. This has brought the green channel down to meet the lowest of the trio. Note that your values are image dependent and you will be changing different channels to different values in real examples you may have. Also note that the values in alongside the girl’s neck strap is 2 a good point to use as it showed data values of: the actual Levels palette are not important – you have to watch the Info Palette.

8. You now have neutral shadows

9. Highlight the green channel, then the highlight end of the Input Levels and arrow down until the 235/235 becomes 235/237 (ie a small change is this example)

10. Highlight the blue channel and then the highlight data entry box of the Input Levels and arrow down until the 222/222 becomes 222/237. Now you have neutral highlights

11. Add a third Color Sampler point to an area which should be a mid-tone neutral. In this case the area

12. Make a Curves Adjustment Layer. Highlight the red channel, then click anywhere near the middle of the curve, to add a Control Point on the curve and bring out the Input and Output data-entry boxes. Type the red input value of 127 in the top box and the aim output value of 112 in the output box.

13. Move to the blue channel and click a Control Point, then type the input value of 112 and the output value of 127.

14. The last two moves have the effect of neutralising the highlights.

When you perform this operation you will find that the adjustments affect each other and you could find that the curve moves have shifted your (formerly neutralised) shadows and highlights. If this is the case go back and tweak them as necessary.

The final adjustment that we made was to go back and adjust the overall levels in the RGB composite channel to bring up the contrast. We did this by holding down the Alt key while using the highlight and then the shadow slider to reveal the highlight clipping point and the shadow clipping point (ie vales reaching over 255 and down to zero RGB points).

Although the procedure seems complex when written down (DVD-movie is a far better medium to learn this trick!) once you have done it a couple of times it becomes second nature and is certainly faster than grinding the Colour Balance box endlessly as you attempt to second-guess what the colour bias is – this method measures it and removes the user’s eyes from the equation – often a good idea!

Below: The Photo Filter (from the Image>Adjust menu) produces global colour shifts which which makes it unsuitable for crossed curves. It does however have uses, especially if applied via an Adjustment Layer so that you can exploit the built-in mask. You could try this if only a bride's dress was a little cool, eg when photographed in open shade.

Keep it Simple!

There are other, simpler methods of approaching colour balance problems which may work in some circumstances and are certainly worth a try – always go for the simplest, fastest way to get a job done unless you have reason to be fanatically careful about the colour.

If you are sure that the colour bias is a simple, single colour one you could try the Photo Filter in the Image>Adjust dialogue menu. This is very useful if you want a quick method of lifting the warmth of a portrait. However it did not work with the test image used in this feature.

We tried Snap Neutral Midtones in the Levels dialogue box with a visually pleasing result, but the effect was not as controlled as the more complex method described first. The results are tabulated and show errors of 5 or 6 RGB points. However it might do for proofing or for less critical conditions.

Using Image Adjust Auto Colour was also tested, again with reasonable, but not perfect, results. The results are tabulated and show errors of up to 19 RGB points.

The SWPP 2008 Convention was an outstanding success,
we have 191 days to get ready for the 2009 convention - which starts on January 14, 2009

Photo Quote: More varied than any landscape was the landscape in the sky, with islands of gold and silver, peninsulas of apricot and rose against a background of many shades of turquoise and azure. - Cecil Beaton