Noise Performance
The issue of noise is particularly relevant to this comparison since the cameras have different sensor dimensions. Typically, larger sensors house larger pixels and have better noise control. Noise is an unavoidable side effect of turning up the gain on sensor information. Imagine making a recording of a conversation in a restaurant. The signal, your conversation, is playing against the background noise in the restaurant. If the conversation is quiet, and you turn up the volume, you’re turning up the volume of the background noise too. This is exactly what’s happening when you turn up the ISO - you’re working with a lower signal, and turning it up, trying to avoid hearing the background in the process.

Typically, noise and ISO processing is a case of burning the candle at both ends. You’re going to have to give something up - either color accuracy, grain and smoothness, or fine detail. The secret is to make the best balance of tradeoffs, and these three cameras give us three interesting and contrasting approaches.

 
Take a look at this chart. This is, after all is said and done, a graph of the cumulative results of our noise testing. Essentially it takes several factors into account and adds them all up. The best results are the lowest, indicating that the noise “grain” is the smoothest. The Nikon is clearly the winner here, and the Olympus is not very impressive. There are a few things about this that should be noted, however.

First, keep in mind the ISO 200-800 range is where most people are shooting. The Canon and Olympus are performing in pretty similar ways up to ISO 400, then, at ISO 800 the Canon T1i’s noise control improves, approaching the Nikon D5000. From there, the D5000 and T1i track along pretty well, while the E-P1’s noise levels get steadily higher.
 

Nikon D5000, ISO 1600

Canon T1i, ISO 1600

Olympus E-P1, ISO 1600

This may seem like pixel-peeping, but it’s really not. If you look at the at ISO 1600 samples above, you’re going to see some pretty dramatic differences between the three. The Nikon D5000 has far better tones in the mid-to-low values, while the Olympus E-P1 has noticeable, and objectionable noise. The Canon T1i falls in the middle. Interestingly, when you look at the apparent sharpness of the image, the Nikon seems almost soft- out of focus, or lower resolution. This is not a problem with the focus or the lens however; it’s simply the result of the camera’s more aggressive noise processing. As we said, something has to give. Nikon is controlling the noise, and giving up some crispness in the file. Olympus is at the high end of the scale and not really even in the ballgame. Canon sits in the middle.