Image Sensors

What are images sensors

These are the chips inside the camera that record an image and then turn them into electrical signals. This is the modern day equivalent of film which was used in the earlier days of photography but use a similar principle

A digital camera has a sensor that converts light into electrical charges. The sensors capture light in varying amounts which are then converted into electrical signals and then these are then converted into 1's and 0's which are then combined to form a digital image

The end result is an digitised image which can then be viewed on a variety off display devices including computers,tv's,screens,projectors  etc


My camera a Canon 7D uses a CMOS type sensor to record and transform images which is also a APS c sensor which is a lot smaller than the full frame sensor which is used by it's big brother the Canon 5 D (See top image)


I have included the two images below to give a rough idea of how image capture works

CCD and CMOS Sensors There are the 2 types of image sensors in use today on all digital cameras. I have outlined some of their of differences below:

CCD Sensor

CCDs use a special manufacturing process to create the ability to transport charges across the chip without distortion. This process leads to very high-quality sensor light sensitivity. 

• CCD sensors, as mentioned above, create high-quality, low-noise images. CMOS sensors, traditionally, are more susceptible to noise.
• CCDs use a process that consumes lots of power. CCDs consume as much as 100 times more power than an equivalent CMOS sensor.

Cmos Sensor

Some cameras use (CMOS) complementary metal oxide semiconductor  technology instead of the CCD technologgy

• CMOS traditionally consumes little power. Implementing a sensor in CMOS yields a low-power sensor.
• CMOS chips can be fabricated on just about any standard silicon production line, so they tend to be extremely inexpensive compared to CCD sensors.CCD sensors have been mass produced for a longer period of time, so they are more mature. They tend to have higher quality and more pixels.
• Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip tends to be lower. Many of the photons hitting the chip hit the transistors instead of the photodiode.

I have included two images above which show the two different types of sensor although they look the same in appearance they are quite different in technology

Both CCD and CMOS image sensors convert light into electrons. Once the sensor converts the light into electrons, it reads the value of each cell in the image then records this information onto the chip which is then transffered from the chip to the memory card in the camera which is recorded as a digital image

Shown below are some details of the image sensor that is installed in my Canon 7D camera. This is a C-Mos type sensor which stands for Complimentary Metal Oxide Semiconductor. This name is given mainly to the electrical circuitricy which is also used in PC construction

Cmos use less power consumption than CCD sensors and are are also cheaper to manifacture

Shown below is an image and information on the Canon 5d's sensor. Although the 5d lacks the speed and processing power of the 7D with it's 2 Digic 4 processors the 5D produces much more smoother images with far superior clarity.

Two of my colleagues both have a 5D's and I would agree with them both,that there images give better clarity  and better tonal ranges than my 7D. 

The image sensor in a Canon 5D is a lot larger than the sensor in a 7D. This explains why the 5D is more expensive than the 7D but the larger size sensor does produce better images. With a camera you get what you pay for so I'm saving now for the Canon 5D mk 3

Shown below is some of the research that I have carried out on the two different types of sensor used in today's digital cameras


Differences between the two types of sensors lead to a number of pros and cons:

• A CCD transports the charge across the chip and reads it at one corner of the array. An analog-to-digital converter (ADC) then turns each pixel's value into a digital value by measuring the amount of charge at each photosite and converting that measurement to binary form.
• CMOS devices use several transistors at each pixel to amplify and move the charge using more traditional wires. 

• CCD sensors create high-quality, low-noise images. CMOS sensors are generally more susceptible to noise.
• Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip is lower. Many of the photons hit the transistors instead of the photodiode.
• CMOS sensors traditionally consume little power. CCDs, on the other hand, use a process that consumes lots of power. CCDs consume as much as 100 times more power than an equivalent CMOS sensor.
• CCD sensors have been mass produced for a longer period of time, so they are more mature. They tend to have higher quality pixels, and more of them.

Although numerous differences exist between the two sensors, they both play the same role in the camera -- they turn light into electricity.

Shown below is a chart showing the different sizes of image sensors that are used in todays digital cameras

Sensors used in digital cameras

Width	Height	Aspect ratio	Actual pixel count	Megapixels	Camera examples
320	240		76,800	0.07	Steven Sasson Prototype (1975)
640	480		307,200	0.3	Apple QuickTake 100 (1994)
832	608		505,856	0.5	Canon Powershot 600 (1996)
1,024	768		786,432	0.8	Olympus D-300L (1996)
1,280	960		1,228,800	1.3	Fujifilm DS-300 (1997)
1,280	1,024	5:4	1,310,720	1.3	Fujifilm MX-700 / Leica Digilux (1998), Fujifilm MX-1700 (1999) / Leica Digilux Zoom (2000)
1,600	1,200		1,920,000	2	Nikon Coolpix 950
1,600	1,200		1,920,000	2	Samsung GT-S3500
2,012	1,324		2,663,888	2.74	Nikon D1
2,048	1,536		3,145,728	3	Canon PowerShot A75, Nikon Coolpix 995
2,272	1,704		3,871,488	4	Olympus Stylus 410, Contax i4R (although CCD is actually square 2,272x2,272)
2,464	1,648		4,060,672	4.1	Canon 1D
2,560	1,920		4,915,200	5	Olympus E-1, Sony Cyber-shot DSC-F707, Sony Cyber-shot DSC-F717
2,816	2,112		5,947,392	6	Olympus Stylus 600 Digital
3,008	2,000		6,016,000	6	Nikon D40, D50, D70, D70s, Pentax K100D
3,072	2,048		6,291,456	6.3	Canon 300D, Canon 10D
3,072	2,304		7,077,888	7	Olympus FE-210, Canon PowerShot A620
3,456	2,304		7,962,624	8	Canon 350D
3,264	2,448		7,990,272	8	Olympus E-500, Olympus SP-350, Canon PowerShot A720 IS
3,504	2,336		8,185,344	8.2	Canon 30D, Canon 1D II, Canon 1D II N
3,520	2,344		8,250,880	8.25	Canon 20D
3,648	2,736		9,980,928	10	Olympus E-410, Olympus E-510, Panasonic FZ50, Fujifilm FinePix HS10
3,872	2,592		10,036,224	10	Nikon D40x, Nikon D60, Nikon D3000, Nikon D200, Nikon D80, Pentax K10D, Pentax K200D, Sony Alpha A100
3,888	2,592		10,077,696	10.1	Canon 400D, Canon 40D
4,064	2,704		10,989,056	11	Canon 1Ds
4,000	3,000		12,000,000	12	Canon Powershot G9, Fujifilm FinePix S200EXR
4,256	2,832		12,052,992	12.1	Nikon D3, Nikon D3S, Nikon D700, Fujifilm FinePix S5 Pro
4,272	2,848		12,166,656	12.2	Canon 450D
4,032	3,024		12,192,768	12.2	Olympus PEN E-P1
4,288	2,848		12,212,224	12.2	Nikon D2Xs/D2X, Nikon D300, Nikon D90, Nikon D5000, Pentax K-x
4,900	2,580	16:9	12,642,000	12.6	RED ONE Mysterium
4,368	2,912		12,719,616	12.7	Canon 5D
7,920 (2,640 × 3)	1,760		13,939,200	13.9	Sigma SD14, Sigma DP1 (3 layers of pixels, 4.7 MP per layer, in Foveon X3 sensor)
4,672	3,104		14,501,888	14.5	Pentax K20D, Pentax K-7
4,752	3,168		15,054,336	15.1	Canon EOS 500D, Canon EOS 50D
4,928	3,262		16,075,136	16.1	Nikon D7000, Pentax K-5
4,992	3,328		16,613,376	16.6	Canon 1Ds II, Canon 1D Mark IV
5,184	3,456		17,915,904	17.9	Canon EOS 550D, Canon EOS 60D, Canon EOS 7D
5,270	3,516		18,529,320	18.5	Leica M9
5,616	3,744		21,026,304	21.0	Canon 1Ds III, Canon 5D Mark II
6,048	4,032		24,385,536	24.4	Sony α 850, Sony α 900, Nikon D3X
7,500	5,000		37,500,000	37.5	Leica S2
7,212	5,142		39,031,344	39.0	Hasselblad H3DII-39
7,216	5,412		39,052,992	39.1	Leica RCD100
8,176	6,132		50,135,232	50.1	Hasselblad H3DII-50
11,250	5,000	9:4	56,250,000	56.3	Better Light 4000E-HS
8,956	6,708		60,076,848	60.1	Hasselblad H4D-60
8,984	6,732		60,480,288	60.5	Phase One P65+
10,320	7,752		80,000,640	80	Leaf Aptus-II 12
9,372	9,372	1:1	87,834,384	87.8	Leica RC30
12,600	10,500	6:5	132,300,000	132.3	Phase One PowerPhase FX/FX+
18,000	8,000	9:4	144,000,000	144	Better Light 6000-HS/6000E-HS
21,250	7,500	17:6	159,375,000	159.4	Seitz 6x17 Digital
18,000	12,000		216,000,000	216	Better Light Super 6K-HS
24,000	15,990	2,400:1,599	383,760,000	383.8	Better Light Super 8K-HS
30,600	13,600	9:4	416,160,000	416.2	Better Light Super 10K-HS
62,830	7,500	6,283:750	471,225,000	471.2	Seitz Roundshot D3 (80 mm lens)
62,830	13,500	6,283:1,350	848,205,000	848.2	Seitz Roundshot D3 (110 mm lens)
38,000	38,000	1:1	1,444,000,000	1,444	Pan-STARRS PS1
157,000	18,000	157:18	2,826,000,000	2,826	Better Light 300 mm lens Digital