Getting to know your digital SLR is mostly an exercise limited to numbers pertaining to shutter speed, ISO (sensitivity of the sensor) or aperture. You seldom get to hear about the complex and intricate image sensors and the intelligence stored in the many digital processors that power your DSLR.
The skill of the photographer aside, it is this complex electronic circuitry that captures that perfect moment for posterity.
The 35-mm films used to retain light captured through the lenses in analog cameras are yet to be matched by the digital image sensors. Most cameras use smaller sensors and hence capture lessinformation. Of late, DSLRs have started sporting the 35-mm digital image sensors. These sensors, called the full frame digital sensors, comprise more number of charge coupled devices (CCD), yielding images of resolution up to 39 megapixels.
The light collected from the image sensors can be stored either as raw images, which in a 16 megapixel camera can be up to 60 MB, and when stored as JPEG files it can be compressed to around 4 MB. DSLRs are capable of storing images in both raw and JPEG formats simultaneously. The JPEG compression, which reduces the memory footprint to one-tenth, requires enormous computation. The digital signal processor (DSP) designed using logical gates is part of the processor, and performs these computations and other image enhancements, if asked for, at tremendous speeds.
In cellphone cameras or point-and-shoot cameras the lag between clicking consecutive pictures is an annoyance. The lag between pictures can eclipse what could have been wonderful shots. DSLRs have the option of the highest burst mode capture. Burst mode capabilities are not only dependent on how fast a processor is housed in the DSLR, but also is a function of the cache memory, or the temporary storage, where the processor dumps pictures before unloading it onto the secure digital (SD) memory cards. In most DSLR cameras, burst mode can easily capture seven frames per second.
After the click
The processor, apart from clicking and storing the images, performs complex signal processing of the images. Advanced image processing of images such as weaving images taken at multiple exposures to generate high dynamic ranging (HDR) images can be done onboard by the processor.
The onboard processor also has the ability to control the mechanical motion of the lenses. The servo motors, which either reside in the body of the camera or in the lenses, can be controlled by the main processor when attempting to focus on an image.
The face and smile detection feature, now common in point-and-shoot cameras, is taken to the next level with options like multiple focus points. DSLR cameras can focus on few tens of distinct points in an image. For instance, in a 11-point focus image, the processor has to send out its analysis such as the average exposure to 11 different points to get the best shot.
Ashfaq Farooqui, an avid photographer says it is not always that a photographer shops for a camera looking for the image sensor or the processor directly. “In comparing DSLR cameras, aspects such as ISO, bit depth, crop factor, number of auto points and burst mode features are used. These are direct consequences of the potential of the sensor and the processor used in the camera,” he says.
Speed, lower power consumption and computation needs are driving companies such as Nikon and Canon to invent better performing processors and sensors. The latest in the Nikon’s Expeed series of processors Expeed 3A can capture up to 60 frames per second when interfaced with a 14 megapixel sensor; that is close to 850 megapixels per second.