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I'm actually serious about number 7, as both factors can play a significant part in the image quality equation. The time of day (or night) affects the amount of natural light in most scenes, and determines the need for flash or increased ISO. The weather helps determine how hot or cold both you and the camera are when taking pictures. When the ISO on a camera is adjusted to make it more sensitive in low light, you increase image noise and decrease image quality. Image noise also increases when a digital camera gets warmer, and decreases when it gets colder. And if you're cold, shivering increases blur.
The design and size of the imaging sensor, combined with the image processing technology built into a camera, help determine the potential resolution (sharpness), contrast, and color accuracy of a images from a camera. Compression can remove details or cause weird edges and artifacts, and camera settings can affect everything from sharpness to color saturation. If a camera has a lousy autofocus system, an 8 megapixel camera can act like a 2MP camera, while metering and white balance systems help determine exposure accuracy and realistic color. Then there's the lens, which can also affect image sharpness, plus strange things like distortion and chromatic aberrations that further degrade an image.
In future McNamara Reports, I'll take a closer look at each of these image quality components. But first I wanted to show a side-by-side comparisons of a noise test target shot by two 8MP cameras (both costing over $500, and both set to ISO 400). On the right is an image with relatively low noise. On the left, an image with unacceptably high noise. It should be obvious how noise degrades image quality and resolution, and why purchasing the camera on the right just because it had a high megapixel count would be a mistake.
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