The Big Three: Setting your camera for the best Aperture RAW results
"The negative is comparable to the composer's score and the print to its performance. Each performance differs in subtle ways." -Ansel Adams
Ansel, of course, was working with film negatives and individually produced darkroom-produced prints. In our case, we have the RAW file which can be considered a digital negative. It does not become an image until we make choices on how the image should be displayed. Subtle differences in these choices can have huge effects on the image as viewed on our computer monitor.
Aperture supports the RAW format of several hundred digital cameras. While JPEGS and TIFFs are formats designed to display images, RAW is simply a dump of the raw intensity data at each pixel. Aperture must make many choices and perform a lot of data manipulation in order to turn the raw sensor data into a viewable image.
The manufacturers have an advantage here. They know exactly how their cameras, including all the settings and controls, turn the sensor data into a viewable JPEG image, and their RAW processors can produce an initial image from the RAW file that exactly matches the way the camera would have produced a JPEG. You are free to adjust that image as far as RAW allows, but you will start with an image equivalent to a JPEG the camera would produce.
The Aperture team generally does not have the luxury of knowing exactly how the camera produces the JPEG from the raw sensor data. While each RAW file contains information on all the relevant camera settings, many are hidden in proprietary codes and formats. Aperture tries to decode as many as it can, but the RAW processor for any given camera may have differing levels of ability to reproduce a JPEG equivalent from the RAW data. In some cases, the Aperture team may think they know better and intentionally produce an image different than the JPEG equivalent, anyway.
What actually affects the raw data that goes into the file? How should you set your camera to get the best results in Aperture? Here are some suggestions for an initial starting point. Feel free to experiment, but you can always come back to these settings to start fresh.
Since the dawn of the camera, the key to a pleasing print has been exposure - how much light gets to the film/sensor and how the film/sensor responds to it. From the beginning, we have had what I call the Big Three: Aperture (how wide the lens opening is), Shutter Speed (The amount of time the light is allowed to hit the sensor) and ISO (How sensitive the sensor is to light intensity). It is beyond the scope of this article, but these three controls establish how much light gets to the sensor and therefore the intensity at each pixel on the sensor. Aperture does not need to know these settings in order to produce a good viewable image, it simply uses the intensities from the RAW file and what it knows of the physics of the camera to produce an image. (We might want to know what the settings are to understand the differences, but Aperture does not care.)
The only other camera setting that matters to Aperture is white balance. Your vision has an amazing ability to correct the colors you perceive based on the color of the light. Cameras must compensate for this and use use white balance to achieve accurate colors no matter the color of the light. It is best to leave the camera at Auto. Aperture does honor some camera's settings in this area, but YMMV. Test it out before you need it, which is good camera advice in general, anyway. White balance is one of the easier things to get right in Aperture!
If the "Big Three" and the white balance were the only settings available, there would be no problem. But as you know there are dozens of other controls and picture tweaks that are available in the camera. Most are ignored by Aperture and are pretty subtle anyway, like the various "vivid" or "sharp" settings. Some settings, such as Canon's Highlight Tone Priority and Nikon's Active D-Lighting are particularly devilish. They silently change the exposure, which makes it into the RAW file, but Aperture does not understand the setting and does not apply the correct tone curve which causes a wrongly exposed result as viewed in Aperture.
To sum up, (the original form of TL;DR!) when first starting out with Aperture and a new camera, it is best to reset the camera to its defaults and use only ISO, Aperture and Shutter Speed with Auto White Balance until you have a good idea how Aperture develops the RAW data for your camera. Especially avoid settings like Highlight Tone Priority and Active D-Lighting that silently change exposure levels and compensate for that with a change in tone curve.
If you are coming to the forum with a RAW issue, please follow the same steps. Reset the camera to its default settings and try to repeat the issue with the Big Three only. Be sure to tell us that you did this in the post.