This month, we have a guest column by Wetpixel Co-Administrator Craig Jones who shoots the Nikon D100 in a Nexus housing. Craig comes from a computer science background – so who better to talk to us about using all of the features in the Adobe Photoshop RAW converter called Adobe Camera Raw (v2.2). This is an “advanced” article with a limited audience, but is becoming more and more applicable as digital photographers start to use the wonderful features of the RAW format.

The following screenshot shows the dialog box that pops up when you click to open a RAW file in Photoshop CS. There are 4 tabs to choose from to make changes that will be applied when the RAW file is converted to a TIFF. They are: Adjust, Detail, Len s, and Calibrate. Craig goes into particular detail about the Len s tab – this is a new and amazing feature that lets the photographer correct chromatic aberration, aka “CA.” Chromatic aberration happens when light passes through an air/water interface, and to a lesser extent through a lens. It is essentially preferential “splitting” of the light beam in the same way as when it passes through a prism, but to a lesser degree. In practical terms what it means is that blue light won't land in the same place as red light – something that is especially important for digital cameras which have red, green, and blue pixels arrayed in a Bayer pattern on the sensor. The corrections in Adobe CS allow the user to compensate for CA and essentially bring the spread out colors back into line. This is a tremendous advantage, especially for macro photography through a flat port which is well known to introduce CA.

The following are Craig's Photoshop CS RAW processing steps:

“(0) Select Adobe RGB, 16 bit, and the desired resolution. I've been up-scaling my images in ACR but like to hear other opinions on that. I set resolution to 300 dpi (remember that that's only embedded metadata). You shouldn't need to do this every time though you should set your camera defaults. Set brightness, exposure, and saturation at 0, shadows at 5 and contrast to 50 or 75.

(1) Use the exposure and contrast sliders to adjust the image to appear roughly exposed properly. This is only necessary for underexposed images (or in the case of Kodak deliberately overexposed ones). It's important during the adjustments not to clip any of the channels so you may need to return to this control from time to time. The "exposure" slider is the overall brightness control while contrast limits dynamic range.

(2) Set white balance. I frequently use the eyedropper for this. For macro with your camera, lenses, and strobes the proper white balance will lie within a normal range of settings so you will eventually know where to set it. Don't be afraid to change it, though, if it doesn't look right. For wide angle, settings vary so the eyedropper is more valuable. If you are using filters keep that in mind, too. Make sure the histograms don't clip on the right while doing this. If they do make some adjustments in step 1.

(3) Now for the hard part. You need to decide how much dynamic range the final image should contain. I frequently limit dynamic range because most images just don't have it, but this is specific to each images. High dynamic range images require low contrast settings and vice versa. Adjust the contrast slider in combination with the exposure slider to set the proper exposure and dynamic range to your liking. Don't worry yet about brightness (the image may seem too dark at this point). Hold down the ALT key while adjusting brightness. This allows you to see precisely when clipping occurs and in which channels. Clipping a pixel is sometimes OK but you should few if any dots when doing this.

(4) Adjust the black threshold using the Shadows slider. Occasionally the default value of 5 will be too high but generally (for my D100) its not nearly enough. Hold down the ALT key while adjusting this control and you will see which pixels are getting truncated to 0. As long as the image is all white your Shadow setting is too low. For images with a lot of backscatter, raising the Shadow level will seriously improve matters but at the cost of lost shadow detail. Don't be afraid to raise this value but make sure you err on the low side.

(5) Use the brightness control to adjust the overall brightness of the image if necessary. I generally leave this set at 0 and increase it only when necessary. Doing so may require you to adjust the exposure slider downward.

(6) Adjust saturation to taste. I'm always using at least +10 saturation and sometimes more (or much more). I've use +100 often enough so don't worry about it. Adjusting this slider will probably dictate adjustments in steps 3, 4 and 5. In reality, all these controls interrelate so you have set them all together. I generally start with the one furthest out first and set saturation fairly early on.

You should now have an image that has its basic adjustments done. Proceed now to the "Detail" tab.

I don't personally adjust this from image to image but simple set sharpness and luminance smoothing to 0 and color noise reduction to 25 (probably the ACR default). Cameras are different and when I switch to Kodak I expect to have to adjust these values for each image.

Proceed to the Lens tab and do the following:

(1) Look in the corners (or as far away from the image center as possible) and find an area of high monochrome contrast. Using the zoom tool select a small portion of the image that displays some detail.

(2) Adjust the two chromatic aberration sliders while carefully observing the effect on the zoomed area. If you are adjusting an image shot using a good wide angle lens and a dome port, this step may be unnecessary, but macro shots with flat ports will receive a noticable benefit from this. The two sliders adjust the Red and the Blue relative to the Green, so study the effect carefully to determine what is going on, then adjust with the goal of converging all three colors. On my D100 high magnification macro shots, settings around +80 are common for both sliders. For the 5050/PT-015 and macro, the sliders are usually pegged at +100 (need about +125 for this setup). CA on the PT-015 is massive.

(3) I don't personally have a need for the vignetting control so I've never used it. I wouldn't hesitate if I thought it were a problem though. I'd take a test shot of an all-white subject for that.

That's it. Once converted, I generally only make fine exposure/gamma adjustments using levels, set my blacks using levels or channel mixer, then make fine color balance adjustments. A common adustment is using the cyan range of the hue/saturation control to improve blues and I occasionally do selective adjustments (either through dodge/burn, selection tools, or adjustment layers and the eraser). I don't use curves. The rest of my adjustments are mostly backscatter removal and sharpening.” [Craig Jones]