Adjusting RAW vs. Non-RAW Images


You've already seen how the White Balance controls (the Temp and Tint sliders) can be used to correct the white balance and other color problems in a RAW image. However, these controls behave a little differently as you switch between RAW and non-RAW images such as TIFF, JPEG, or Photoshop files.

Light has inherent color qualities. These qualities are measured using a temperature scale. When you change the white-balance setting in your camera, you're simply letting your camera know a little more about the color of the light under which you are shooting. The information is used by your camera to calibrate its color calculations so that they will be more accurate.

When you open a RAW file in Aperture, the first thing the application does is calculate the color of every pixel in your image. It uses the temperature and tint settings that you (or your camera) specified as image metadata to calibrate its settings for the color of the light you were shooting under. When you change these settings, you're doing nothing more than changing the calibration reference that Aperture uses for its calculations.

In a non-RAW file (a JPEG, TIFF, or Photoshop file, for example) the color of every pixel is already set. The white-balance calculation was made by your camera when you took the shot, and can no longer be altered.

In Aperture, therefore, when you adjust the Temp or Tint sliders while editing a non-RAW file, the program has to work with existing color information and adjust existing pixel colors. It can't simply alter the fundamental color calibration. Unfortunately, altering existing colors is more complicated than simply recalibrating during a RAW conversion, as you'll see in this example.

1.

With the Lesson 09 Images item selected in the Projects panel, press Command-Option-S to switch to Standard layout. Then, press I to open the Adjustments and Metadata Inspectors.

2.

In the Browser, select the image dafnis for bad wb jpeg. As you can see, this image has a white-balance problem. We'll try to correct it using the White Balance controls.

3.

Still in the Browser, Command-click the image dafnis for bad wb raw. This is a copy of the same image, but one that was shot with the correct white balance. We'll use it as a reference for our correction efforts.

4.

In the Viewer, click the image dafnis for bad wb jpeg to make it the primary selection.

The image is plainly too blue, so we'll use the Temp slider to skew the image's color toward yellow.

5.

In the White Balance controls in the Adjustments Inspector, drag the Temp slider to the right to about 9185. This helps the image a lot, but it's getting a little too pink.

6.

Move the Tint slider to the right until the Tint value field says 10. This removes some of the pink from the image, but the color is still not quite the same as in our correct image.

7.

Play with the sliders some more and see how close you can get the image to the correct white balance. You'll find that it's difficult to get it there. What's more, as you get more accurate skin tones, you'll be adding a color cast to the white of the clouds and altering the blue hue of the sky.

Simply put: the White Balance controls are not nearly as effective on a non-RAW file as they are on a RAW file. What's more, by the time you're done adjusting a non-RAW file using the White Balance controls, you will have used up a lot of the editing latitude in your image. As a result, any further adjustments could very well result in posterization and tone breaks in your image.

Let's take another look at how white-balance adjustments differ between RAW and non-RAW images.

8.

In the Browser, click to select the boat jpeg image, and then Command-click to also select the boat raw image.

Two versions of the same image appear. The image on the left is a JPEG copy of the RAW file that's shown on the right.

9.

In the Viewer, click the left-hand image (the JPEG file) to make it the primary selection.

10.

In the White Balance controls, drag the Temp slider all the way to the left, until the temperature value reads 2500 K.

11.

Now click to make the right-hand image (the RAW file) the primary selection and set its temperature value to 2500 K.

While both images now have a strong blue cast, you should see that the colors are still quite different. In the JPEG image, the blue cast doesn't go through all of the different color ranges as thoroughly as it does in the RAW file. In the JPEG image, the red on the bottom of the boat is much redder than in the RAW file. The same is true of the greens in the background.

What you've seen from these exercises is that the white-balance adjustment packs a lot more power when you're working with RAW files. If you're shooting RAW, then, you should be sure to make all of your white-balance adjustments in RAW format before you save to any other formats.

Similarly, if you're working with JPEG files, don't expect to be able to make the same type of dramatic white-balance corrections that you can make with a RAW file. When working with JPEGs, you may need to rely more on the Tint wheels than on the White Balance controls for your color corrections.




Apple Pro Training Series(c) Aperture
Apple Pro Training Series: Aperture
ISBN: 0321422767
EAN: 2147483647
Year: 2004
Pages: 185

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