stars | Strolls with my Dog

This article and the following one will discuss the effect on resolution of digitizing a continuous optical image.

The sampling process carried out by the sensor results in digital values corresponding to an intensity at each pixel’s location. These so-called Data Numbers are stored ideally as-is in the raw file and are proportional to infinitesimal point samples of a new continuous image: the optical image smoothed by the characteristics of the pixels’ effective active area, known as the pixel aperture function.

Figure 1. Simulated Pixel Aperture Function of a 4um pitch Back Side Illuminated pixel in isolation. Note diffusion beyond the -2/+2um theoretical pixel boundaries suggested by pitch.

Smoothing by a finite pixel area reduces resolution. Continue reading Sampling in Imaging →

Now that we know how to open 12-bit raw files captured with the new Raspberry Pi High Quality Camera, we can learn a bit more about the capabilities of its 1/2.3″ Sony IMX477 sensor from a keen photographer’s perspective. The subject is a bit dry, so I will give you the summary upfront. These figures were obtained with my HQ module at room temperature and the raspistill – -raw (-r) command:

Raspberry Pi HQ Camera	raspistill --raw -ag 1	Comments
Black Level	256.3 DN	256.0 - 257.3 based on gain
White Level	4095	Constant throughout
Analog Gain	1	Gain Range 1 - 16
Read Noise	3 e-, gain 1 1.5 e-, gain 16	1.53 DN from black frame 11.50 DN
Clipping (FWC)	8180 e-	at base gain, 3400e-/um^2
Dynamic Range	11.15 stops 11.3 stops	SNR = 1 to Clipping Read Noise to Clipping
System Gain	0.47 DN/e-	at base analog gain
Star Eater Algorithm	Partly Defeatable	All channels - from base gain and from min shutter speed
Low Pass Filter	Yes	All channels - from base gain and from min shutter speed

Continue reading Pi HQ Cam Sensor Performance →

Musings about Photography