To add to Itai's great answer, Micro-contrast is an aspect of digital photography that is extremely vulnerable to anti-alias filters, or low-pass filters. A digital image sensor is only capable of processing information down to a certain limit (the Nyquist Limit), after which any additional information will be captured as undefined or ill-defined "noise". This undefined information can be a great detriment to image quality for high density sensors such as those found in your average DSLR. A low pass filter is often placed in front of a digital sensor to eliminate image frequencies below the limit of a sensor. Poorly or cheaply designed filters can have a visible and detrimental effect on micro-contrast in the other direction...softening an image and reducing its sharpness.
Larger format sensors have the benefit of high resolution and lower density on their side. With larger pixels, the need for a low pass filter is greatly lowered, and they are usually eliminated entirely. This allows larger format sensors to achieve much greater micro-contrast...contrast differentiation between individual pixels, than is usually possible with smaller format sensors such as APS-C and Full Frame.