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

Technical Evaluation of my final prints

I decided to have my final images printed on-line by a a reputable Photo Printing company D C Colour labs from Manchester. I have used this company many times before and overall I find their printing to be very good with a very reliable service. I have discussed this company in more detail in some of my other blogs in the module (310) photo imaging output 

On receipt of my images I gave them a thorough inspection for quality and overall condition. I was fairly pleased with the overall printing of the images. I would award them 7/10 on the overall printing of my photos. I awarded them a score of 7 because overall for the price of £1.05 for an A3 print I consider this was fairly good value for money and  I wouldn't expext the quality to be any better at this price

To evaluate the prints I would say that the images are a little on the dark side and are not exactly the same brightness as seen on my pc monitor. They lack a little vibrancy and the clarity is not perfect even though I did I did download and send my images for print using the print company's ICC profile.There are no banding marks evident, no surface marks or scratches. Colours seem to be a fairly true to my originals and there are no colour casts evident. The paper they use is a Lustre paper which seems to display the image with a smooth texture. With choosing a print size of A3 obviously the images look better when viewed from a distance and seem a little soft on the focus when viewed close up

The company gave a requested image size of 4950 X 3510 pixels to print an A3 image with no cropping evident. I configured these dimensions in Photoshop and then saved the image files with their recommended ICC profile and dimensions

Shown below is my image loaded into the company's software before the image is processed for print. You can choose image size,papers,quantity etc from here

The image above shows a part of DC's printing software before the image is finally processed before print. This is a very important part of the software because you can see here how your final image will look before being printed and make final adjustments to get the best out of your prints

On inspection of my final prints I did notice that a couple of my images seem to be a liitle stretched an pix-elated even though I had sized and saved all of my images to the correct dimensions recommended by the company. I was mistified by this and have been analizing this problem over a couple of days. On closer inspection I did find the route of the problem. The two images that were pix-elated had been cropped earlir in Phtotoshop by myself to different pixel dimentions. When I resized them in Photoshop ready for print to the companies given dimensions,the images were being stretched which resulted in pix-elation which also resulted in the prints having a a squashed appearance. I will be aware of this problem next time I send them to print and found this to be a good learning curve

For speed and delivery I would award the company 10/10. I uploaded my images and placed my order 10.00pm on a Sunday night and received them the1st thing on the following Tuesday, approx 34 hours for the whole process,brilliant!!


The overall cost of producing my final 20 images did come into the equation. At D C Colour labs the overall cost to print these 20 images was £25.00 including delivery. In Comparison,to print the same amount of images in college to a similar standard would have cost me £80.00 including test prints


Overall I would have preferred to print my images using the college's printer because I would have had full control of colour management and the advantage of printing my images from a Raw\Psd file which retains more clarity and better definition. However costs won over clarity on the day and for the service they provide I find them excellent value for money

Equipment used for my portraits

I have chosen the subject of portraits for my second set of images and have produced a set of images with the theme on street performers. I have captured a lot of images from various locations in and around the UK. One of my latest visits was to Whitby Gothic festival which is a twice yearly festival where Goths and other people come fom all over the country congrigate and dress dresss up for the day in the costumes of their choice

For any budding portrait photographer this is absolute must where you can gain a variety of experience of this type of photography

Shown below is the equipment that I used for the weekend

Cameras

Canon 7D DSLR 

Lenses :

Canon 70-210 F4 zoom lens

Canon 18-55 Wide angle zoom lens


Other Equipment

Velbon tripod
Compact Flash memory cards
Phototoshop CS3 software for image manipulation
Desktop pc and Sony laptop for image manipulation and downloading images

The majority of my images were captured with my Canon70-200 F4 zoom lens. I used this particular lens as I wanted to move in close to my subjects for some really good head and shoulder shots.


Using an F stop of F4 allowed me to create a really shallow depth of field which created a really nice blurred background behind my subject which isolated the subject from it's background


In comparison I would have preferred to use a faster lens with an aperture of 2.8. Using a lens this fast would have allowed me to to generate an even greater blurred background which makes your subject stand out even more from your background.