Chapter 4- Image Capture Mediums- Film and CCD/CMOS Sensors

Question 1

Monochrome film- Describe the physical structure of the film.

Answer 1

The light-sensitive layer of photographic emulsion (silver halide suspended in gelatin medium) is coated onto a clear substrate material (e.g cellulose triacetate, PET or PEN).

Question 2

Monochrome film- Prior to the following stages of manufacture, untreated silver halide crystals are only sensitive to the blue and ultra violet region of the spectrum, resulting in blue subjects looking white and other colours looking much darker. What 5 stages are now used to treat the silver halide crystals to make a photographic emulsion?

Answer 2

Emulsification
First ripening
Emulsion washing
Second ripening
Dye sensitisation

Question 3

Monochrome film- What is the resulting emulsion described as (in reference to colour sensitivity)?

Answer 3

Panchromatic (sensitive to all colours of the visible spectrum)

Question 4

Monochrome film- What is Orthochromatic film?

Answer 4

Graphic art film designed for copying that is insensitive to red light
There is also film emulsions available that are sensitive to the infra-red region of the spectrum

Question 5

Monochromatic film-What is Latent Image Formation?

Answer 5

The process by which minor specks of atomic silver is generated after silver halide grains/crystals are exposed to light

Question 6

Monochromatic film-What is a ‘Latent Image’ and what technique is it detected by?

Answer 6

A latent image is an invisible image formed from the silver formation however it is not visible to the human eye. It must be detected through a technique called Electron Spin Resonance (ESP)

Question 7

Monochromatic film-The film development process is essentially a reduction and amplification process. Explain how.

Answer 7

During the chemical development, the silver halide struck by light during exposure are reduced to metallic silver. The individual specks formed on the crystals expand until each crystal has turned black. In addition, in well-exposed regions, individual crystals stick together. This is why it can be considered an amplification process; as the development increases minor levels of silver present by a million times

Question 8

Monochromatic film-The final stage of the development is fixation to make the image permanent. What does this involve?

Answer 8

Removal of any unexposed silver halide crystals, which would darken the overall image if present. These are removed by transforming into soluble compounds and washed away. The film is then dried and the result is a negative

Question 9

Monochromatic film-Who are the main manufacturers of monochrome reversal film?

Answer 9

Ilford, Kodak, Fujifilm

Question 10

Monochromatic film-Why is there an ‘anti-halation backing’ on monochromatic negative film?

Answer 10

Light used to bounce off the back and cause a halo shape/effect so this layer counteracts it

Question 11

Monochromatic film-What do more advanced types of monochromatic film have?

Answer 11

Mixtures of different crystal layers (e.g tabular grains and dimensional grains)

Question 12

Colour NEGATIVE film-Colour negative film is coated with a number of emulsion layers, in which order are they?

Answer 12

The uppermost emulsion layer is sensitive to blue light and ultraviolet radiation.
Layer two is a yellow filter layer (a non light-sensitive yellow dye) which is to block the blue from penetrating to the two lower layers.
The next emulsion layer is sensitive to green light.
Layer four is a red/pink dye filter layer.
The final layer is sensitive to red light

Question 13

Colour NEGATIVE film- As with monochrome film, exposure to light forms a latent image. What is the difference though with colour film?

Answer 13

A latent image is formed in all three emulsion layers. Blue areas of the image will only form in the blue emulsion layer etc.

Any orange areas will register in both the green and red as it is a mixture

Question 14

Colour NEGATIVE film-The development process is very similar to that in monochrome film. It is the colour development stage that imparts them. How does colour dye form?

Answer 14

The presence of colour couplers between emulsion layers react with the oxidation products of the colour development stage to produce coloured dyes within the individual emulsion layers (the strength of colour proportional to amount of light exposure)

Question 15

Colour NEGATIVE film-
Where is yellow dye formed?
Where is magenta dye formed?
Where is cyan dye formed?

Answer 15

Yellow dye is formed in the blue-sensitive emulsion layer
Magenta dye is formed in the green-sensitive emulsion layer
Cyan dye is formed in the red-sensitive emulsion layer

Question 16

Colour NEGATIVE film-The final bleach-fix stage removes which parts of the film?

Answer 16

All (exposed or not) silver halides, yellow and red filter layers and anti-halation backing- leaving just the layered dye images

Question 17

Colour NEGATIVE film-Many fine art photographers are producing large-format film negatives from original digital images. What quality of colour negative films makes it ideal to work with?

Answer 17

To use in processes such as Cyanotypes, Gum Bichromate and Platinum prints

Colour negatives are widely used due to wide exposure latitude as well as the fact that any colour cast present can be corrected at printing stage

Question 18

Colour POSITIVE film- What is it also referred to as?

Answer 18

Slide or Transparency film

Question 19

Colour POSITIVE film- Is not as popular as colour negative film, but what is it superior in?

Answer 19

Sharpness and colour reproduction- this is due to the fact that it does no need to undergo any further printing stages as the original image is a positive. It also has;
finer grain structure
cleaner/brighter colours

Question 20

Colour POSITIVE film-What are colour negative images intended to be viewed in as oppose to colour positive images?

Answer 20

colour negative- book/ journals
colour positive- projector

(mostly digital now anyway)

Question 21

Colour POSITIVE film- Why is it that colour positive film produces sharper colour images to their negative equivalent?

Answer 21

The unexposed silver grains act as templates for the production of positive dyes. The larger grains are more sensitive to incoming light resulting in them being first to be exposed to light. This means the un-exposed grains will be finer grains and therefore these will act as the templates

Question 22

Colour POSITIVE film-What are two important disadvantage to colour positive film?

Answer 22

Limited exposure latitude and it is sensitive to vagaries of light and therefore often requires added filtration

Certain manufacturers produce films specifically for certain types of light, e.g tungsten lighting and therefore denote their film with a ‘T’

Question 23

CCD/CMOS Imaging Sensors- Digital cameras contain either one of these instead of film. What is a CCD made from and what does that do?

Answer 23

A CCD is a light-sensitive sensor that has a light-sensitive surface containing a few million picture elements (pixels), which are equivalent to silver halide crystals on film. The light-sensitive semiconductor material converts light energy falling onto it into an electrical potential

Question 24

CCD/CMOS Imaging Sensors-What is a common pixel size?

Answer 24

1.75 micrometers, with 1.4 being introduced (one company has introduced 1.1 prototype)

Question 25

CCD/CMOS Imaging Sensors- Describe how a CCD DSLR camera works when the shutter button is pressed.

Answer 25

Camera shutter opens and light enters the silicon substrate at the photo sites. Individuals pixels accumulate electrons in proportion to the light level received.
Due to charge-coulping (that’s where CCD gets its name), the electrical charges move along a well defined pathway to an electrode where the charges then revert to analogue electrical signals. These charge signals are then moved down the full array of electrodes to the analogue-to-digital converter (A/D) at the end of each row. Thus a CCD image sensor is an analogue receiver

Question 26

CCD/CMOS Imaging Sensors- What is a CMOS? How does it work compared to a CCD?

Answer 26

A CMOS chip is a type of active pizel sensor which is produced using the CMOS semiconductor process. Each photo site is independent of its neighbour, resulting in random access to each individual pixel via an X-Y address. Also, unlike CCD technology, pixel reading is non-destructive, with the charge remaining on the pixels after initial readings. Each pixel has its own set of transistors to perform amplification and to assist with readout and reset. Entire coloumns or rows can be called out simultaneously

Question 27

What do image sensors to be used in the visible region of the spectrum have?

Answer 27

Infrared filter to restrict their response to the visible region below 670 nm

Question 28

Colour Reproduction Methodology for CCD/CMOS Sensors- A common way of generating colour from a monochrome sensor is by integrating a Bayer filter mask into a CCD/CMOS sensor. What sort of colours does this use? What sort of principle is this?

Answer 28

Red, blue and green- The addtive principle- this enables control of the incoming light for colour reproduction.

Question 29

Colour Reproduction Methodology for CCD/CMOS Sensors-What is the disadvantage of using a Bayer filter in the sensors and why are there more of one colour?

Answer 29

It only records one colour at each pixel site, the other two are added via software interpolation, using a demosaicing algorithm. Also, there are twice as many green sites as blue and red, due to the fact the human eye is more sensitive to green light. This enables the image to appear less noisy and contain finer detail

Question 30

Colour Reproduction Methodology for CCD/CMOS Sensors- The analogue- to-digital converter creates a digital image from CCD. How?

Answer 30

CCD elements undergo quantizationm whereby each step is assigned a unique binary number which represents a specific tone or grey level. Most camera A/D converters convert to 10,12,14 andor 16 grey levels, which is referred to ‘supersampling’ and improves image quality

Question 31

Colour Reproduction Methodology for CCD/CMOS Sensors- What is meant by ‘sequential RGB’?

Answer 31

When the image sensor is read out, line by line, the pixel sequence comes out GRGRGR then alternative line is BGBGBG

Question 32

Colour Reproduction Methodology for CCD/CMOS Sensors-Describe the variations on the Bayer filter’s GBGB/RGRG sequence (most commonly used).

Answer 32

The RGBE filter- Bayer-like with one of the green filters modified to ‘emerald’ (Sony used this for improved colour)
The CYYM filter- one cyan, two yellows and a magenta element. This was used in a limited number of Kodak cameras
The CYGM filter- one cyan, one yellow, one green, one magenta. This was used in a few video cameras
The RGBW bayer- Additional white or transparent filter elements to allow photodiode to respond to all colours of white

Question 33

Colour Reproduction Methodology for CCD/CMOS Sensors-What are sensor microlenses?

Answer 33

Inbuilt elements which direct the light onto the photosites

Question 34

Colour Reproduction Methodology for CCD/CMOS Sensors- What is a Fovean Chip?

Answer 34

A sensor which has the ability to capture RGB at the same time- different wavelength of light penetrate to different layers within the silicon surface

Question 35

Digital Camera Colour Spaces-A colour space is simply a model which describes colours as tupules or numbers or colour components (RGB). Which are the two most commonly chosen ones?

Answer 35

sRGB and Adobe RGB 1998 (Some high end DSLR cameras also offer ProPhoto RGB)

Question 36

Digital Camera Colour Spaces- When would a photographer choose the sRGB colour space and why?

Answer 36

When the photographer is shooting in JPEG. This is because the range of colours in the model are similar to the ones that a computer monitor displays- so when the pics are for a website or going to be shown on a screen

Question 37

Digital Camera Colour Spaces- When would a photographer choose the Adobe RGB 1998 colour space and why?

Answer 37

Offers a larger colour gamut (wider range). Designed for digital printing. However, some printers will not be able to reproduce all the colours of the model

Question 38

Digital Camera Colour Spaces- Do RAW files have a colour space?

Answer 38

No as they do not initially contain pixels. They are a record of unprocessed ‘sensel’ data which exceeds all colour gamut limits- advantageous as it is flexible and the photographer can choose the colour space afterwards

Question 39

Colour Reproduction Quality of Photographic Print Provider-What was found from the study that observed colour reproduction quality of photographic prints produced by prosumer and professional labs?

Answer 39

Only one lab read the embedded profiles correctly
Variation in colour saturation observed
Variation in white balance observed
Labs haven’t fully embraced colour management
sRGB colour space still appears to be default

Question 40

Colour Reproduction Quality of Photographic Print Provider-What are the key features to ensure full colour management of a digital image when producing a photographic print?

Answer 40

Silver halide print: combination of paper and printing exposure device

Photo-realistic inkjet print: the correct combination of inkjet printer, ink set and paper