Tag Archives: demosaicing

Bayer CFA Effect on Sharpness

In this article we shall find that the effect of a Bayer CFA on the spatial frequencies and hence the ‘sharpness’ captured by a sensor compared to those from a corresponding monochrome imager can go from nothing to halving the potentially unaliased range based on the chrominance content of the image projected on the sensing plane and the direction in which the spatial frequencies are being stressed.

A Little Sampling Theory

We know from Goodman[1] and previous articles that the sampled image (I_{s} ) captured in the raw data by a typical current digital camera can be represented mathematically as  the continuous image on the sensing plane (I_{c} ) multiplied by a rectangular lattice of Dirac delta functions positioned at the center of each pixel:

(1)   \begin{equation*} I_{s}(x,y) = I_{c}(x,y) \cdot comb(\frac{x}{p}) \cdot comb(\frac{y}{p}) \end{equation*}

with the comb functions representing the two dimensional grid of delta functions, sampling pitch p apart horizontally and vertically.  To keep things simple the sensing plane is considered here to be the imager’s silicon itself, which sits below microlenses and other filters so the continuous image I_{c} is assumed to incorporate their as well as pixel aperture’s effects. Continue reading Bayer CFA Effect on Sharpness

Raw Converter Sharpening with Sliders at Zero?

I’ve mentioned in the past that I prefer to take spatial resolution measurements directly off the raw information in order to minimize often unknown subjective variables introduced by demosaicing and rendering algorithms unbeknownst to the operator, even when all relevant sliders are zeroed.  In this post we discover that that is indeed the case for ACR/LR process 2010/2012 and for Capture NX-D – while DCRAW appears to be transparent and perform straight out demosaicing with no additional processing without the operator’s knowledge.

Continue reading Raw Converter Sharpening with Sliders at Zero?