In my last tutorial
I gave a quick overview over the user interface of Adobe Camera RAW and I mentioned a couple of the really nice things you can do with it. Today I am going a little deeper. I will be explaining some of the more important functions of Camera RAW, without going into too much detail. I will use the same example of a rather difficult image that requires some curve tweaking to demonstrate some of the capabilities of Camera RAW.
The picture I will be tweaking is not exactly my most glorious photographic example but it serves the purpose nicely.
Often the question arises why I make these adjustments during the RAW conversion process when they are often easier in Photoshop. As I said I don't want to bore the hell out of you with technical details. In short: RAW files represent the data in linear form while a bitmap is a nonlinear processed image that matches our perception of reality better (light levels as seen by the eye). The during the nonlinear processing dynamic range and color information is lost (another reason why I use 16-bit and ProPhoto RGB as indicated in the last tutorial
When you open up an image in ACR (Adobe Camera RAW) you can quickly switch between Auto Settings and default settings by typing Ctrl-U
on the MAC). Usually the Auto settings are a good starting point, although in many situations not perfect.
The Adjust Tab
Often I process a whole folder with automatic settings and use a custom script in photoshop to quickly get results for web publishing. I then pick some images that I feel need further attention to go through the manual adjustment process. This will still give better results than in-camera processing for all images, but leaves me the option to adjust things further.
One of the most useful options is the White Balance adjustment. With this, you will never have to worry about the white balance setting in the field (remember, RAW only includes brightness levels). You can easily adjust the White Balance in the Comfort of your home. When you click on the pulldown menu, you will see the most common light sources defined. Alternatively you can use the white balance eyedropper tool and use it to select an area in your picture that you know is a pure shade of grey (R,G,B should all be at the same value). ACR will then adjust the whitebalance accordingly (don't worry, you can always select "As Shot").
You can play around with all other settings in the Adjustment tab. All settings are pretty much self explainatory. I have found that is is quite possible to have an image that is slightly overexposed and reduce "Exposure" accordingly. How much you can bring back will strongly depend on your camera. The sensor can only record brightness levels up to a maximum. Everything above this maximum will be clipped and information is lost. With the Canon 20D I bring back overexposed areas up to 1 f-stop (Exposure -1 ).
Make adjustments here and observe the results carefully.
I recommend leaving the Saturation slider where it is. There are better methods of boosting Saturation (Digital Veliva Effects) in Photoshop that generally tend to look better.
Sometimes a photographer is faced with a very difficult lighting scene (dark and bright levels). Many of us use tripods to shoot multiple exposures which can be combined in Photoshop. However sometimes it is possible to get a higher dynamic range from just a single shot. Simply extract multiple TIF files from one RAW file, all with different exposure settings (e.g. -2, -1, 0, 1, 2). We can then use Photoshop to combine them to a High Dynamic Range (HDR) image and map it back into the normal range by using curves (I will show how to do this in a later workflow tutorial).
The Detail Tab
Usually I do not touch the detail tab. In fact most stock image agencies don't want you to sharpen your images, since they use their own methods. I generally prefer to sharpen (and reduce noise) inside Photoshop. In Photoshop CS2 Adobe has introduced new tools for sharpening and noise reduction.
The Lens Tab
The sliders in this tab are used to adjust Lens imperfections. Many consumer grade lenses show a tendency for Chromatic Abberations (colored halos that are caused by light bending as it passes through the lens). The effect is similar as going through a prism. It will be visible in areas of abrupt contrast change (something in front of a very bright sky). You need to zoom into the problem area and use these sliders if you intend to fix that. Quite honestly I rarely use these settings.
Vignetting occurs if the borders of your image are darker, because the lens doesn't deliver the same light to the borders of your sensor (due to different angles). Again with a better lens you won't have to adjust anything.
The Curve Tab
With the curves tab you can determine the contrast of the picture. On the x-axis (horizontal) you have the input levels (the levels recorded by your camera) and on the y-axis (vertical) you have the output levels.
You can use the drop down menu to for default contrast settings or you can actually tweak the curve.
So lets tweak the curve to boost the contrast and bring out Mount Hood. After opening the picture it looks like this:
We will now use the Color Sampler Tool and hover over the mountain and the sky. Above the color histogram we will see some numbers, telling us the exact RGB values. Try to find a value where all 3 numbers are roughly equal and remember the number. This is actually our input brightness. If you move over to the curve and move your mouse around, you will see a value in the Input field and a value in the Output field. It turns out that the mountain and the sky are all in that gigantic spike. This is not a surprise, since the height of the spike shows us how many pixels it contains (high spike = large area).
In order to boost the contrast in this area, we will now adjust the curve as shown on the left.
Since we are working with RAW files and now JPG we can boost much more agressive without fear for posterization effects (in 8-bit images there are less brightness levels available, so this kind of adjustment leaves large areas with the same brightness, looking very unnatural). Of course there are limits even in raw.
By adjusting the curve, so that it is very steep around that spike, I boost the contrast in this area. The result is immediately visible by a spread in the color histogram (see circle). If you compare the two images, you can see what dramatic effect this has on the image (if you look closely, you can also see how the color histogram got pulled apart in this area).
This example is a bit extreme. Usually the necessary adjustments are much less pronounced.
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The Calibrate Tab
In this tab you can adjust the Camera Color profile for your camera for more accurate color rendition.
Quite frankly I never considere this necessary.
This concludes this tutorial. In the next tutorial I am going to touch a couple more aspects of raw conversion and then move to the first steps of processing within Photoshop.
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