technical points in photography

Question 1

sensor design

Answer 1

most cameras use a sensor of one of two principle designs
- CMOS- complimentary metal oxides semiconductor
- CCD- charge couple device
both work by converting light into electrical signal
- each sensor will include photo sites or pixels which collect light and turn it into an electrical signal
- a typical sensor will have 8-50 million of these pixels (the more pixels the better resolution)

Question 2

sensor size and the megapixel myth

Answer 2

• the bigger the sensor the better
• a larger sensor normally means larger pixels
• a larger sensor also often offer a greater bit depth- this means that they are capable of differentiating more colours

Question 3

a basic sensor

Answer 3

• the more light the greater the voltage produced up to a point beyond which the pixel is full
• the charge is converted by an analogue to digital converter and is reconstructed to form an image

Question 4

colour sensor

Answer 4

• include a special form of colour filter array known as a bayer filter array
• with a colour sensor things are a bit more complicated and the data gas to undergo a process called demosaicing
• the camera takes data from the surrounding pixels and combines to form a try colour

Question 5

image processing

Answer 5

• the number of different colours a camera can record depends on the bit depth
• 12 bit capture (this means that each colour channel can discern 4096 shades)
• a human can only discern 10 million colours but the high level of performance is due to post processing as this software degrades the final image

Question 6

image processing

Answer 6

once the image has been produced..

- it can be produced to form a jpeg or remain in a raw unprocessed state forming a raw file

Question 7

JPEG files

Answer 7

joint photography experts group

• processed- colour correction, sharpening and well as some exposure correction will have been applied by the camera
• compressed- small file size but the compression process can degrade and robs the images of fine detail particularly in shadow and highlight areas
• converted to 8 bit colour- this means only 256 colour per channel

Question 8

raw files

Answer 8

• unprocessed- requires importing a RAW converter or software such as Lightroom
• often uncompressed- this means file sizes can be huge
• 12 or 14 bit colour
• however as the images are unprocessed some basic work will need doing before being presented

Question 9

post processing

Answer 9

once we have our images

• forensic providers or police download images to secure serve where a hash code is produced
• this prevents tampering or altering of images