Short Answer Questions Flashcards
What are the features of a GIF file format?
Smaller file size
8 bits per channel
Block graphics not photographs
What is the principle of JPEG compression?
Lossy compression
Most commonly used file type
Physically removes pixels
Doesn’t preserve layers
Very small file size
Works well for big complex pictures that use a lot of gradients
Not ideal for images with solid lines or text
What colour conversion does JPEG carry out?
RGB to YCrCB
What does YCrCB stand for?
Luminance, Chroma; Blue; Chroma; Red
What does JPEG stand for?
Joint Photographic Expert Group
What are the positives of JPEG?
Portable
Compatible with almost every imaging application and ah hardware devices
High resolution and fast moving images = no blur
Used on a camera
Suitable for over internet transfer
Down to 5% of original file size
What are the negatives of JPEG?
Lossy compression
Quality reduction
Doesn’t support layered images
High resolution cameras support higher resolution
What are the advantages of describing colour using language?
Universally understandable
Portrayal of emotions
Creative variation
Colour space based on the human visual system
Symbolic uses
20-100 colour description terms can cover most possible needs
What are the disadvantages of describing colour using language?
Not numerical
Subjective
Colour blindness
Difficult to replicate colour spaces reliant on binary
Emotion = difficult to portray numerically
Population dependant
Different meanings across different cultures
What are 2 colour ordering systems based on human perception?
CIELAB + Munsell Colouring System
Describe CIELAB
Colour space by CIE (International Commission of Illumination)
Expresses colour in 3 numerical values
L* = lightness
a= green-red
b= blue-yellow
3D colour space
Integer space with digital representation
Colour differences that you perceive correspond to distance when measured colour metrically
What does each axis represent in CIELAB?
Vertical Axis - extends from 0 (Dark) up to 100 (Light)
Diagonal from Left down to right -a* = green +a* = red
Diagonal from Left up to right -b* = blue +b* = yellow
What is the Munsell colour system?
Colour space based on 3 properties 1. Hue 2. Value (lightness) 3. Chroma (colour purity) Differences from grey at given hue, lightness. Based on perceived "equidistance"
Describe the Munsell colour system?
- Constructed around a circle with 10 segments arranging colours at equal distance
- Opposing pairs result in achromatic mixture
- Irregular cylinder with value axis (light/dark) running up and down through it
- Dark colours at the bottom and light at the top measuring 1 (dark) to 10 (light)
- Horizontal slice of cylinder across axis in a hue circle divided into 5 principles.
What 5 principles is the hue circle in the Munsell colour system divided into?
- yellow
- red
- green
- blue
- purple
What intermediates are the 5 principles in the hue circle in the Munsell colour system divided into?
- yellow-red
- green-yellow
- blue-green
- purple-blue
- red-purple
How is colour specified in the Munsell colour system?
- Specified by selecting one of these 10 hues - referring to the angle inside them fro 0-10.
- Chroma measured out by centre of the wheel w/ lower chroma = less saturated
Why are CMY primaries used in colour printing?
- Subtractive colour mixing.
- CMY colours are often in the form of pigments and inks.
- More colour range.
- More vibrant.
- Important for creating sharper text.
- Better shadow detail.
- RGB can sometimes give an image a pink hue.
- Covers most colour ranges quite easily - compared to using RGB.
Provide two economic reasons why K is often used in conjunction with CMYK inks.
- Cheaper than combining all 3 inks to create black.
- Printer won’t be working as hard - uses less energy and won’t need to be serviced or re-profiled as often.
How does a bi-level printer work?
Process called “dithering” to distribute dots of black and white ink in a pattern varied to simulate different shades of grey.
on/off dot can only be black or white
What 4 factors influence the colour gamut of an inkjet printer?
- Paper type 2. Ink levels 3. Gamut of document 4. Rendering intent used
Why is the quality of an image taken on an SLR camera better than one taken with a compact camera?
- Bigger and better sensor - pixels on a compact camera suffer from interference (noise).
- Can export in RAW format (more bits per channel).
- RAW format allows greater level of detail and allows more flexibility when editing photos earlier on.
- Good for a sequence of moving photos.
- Focuses on the subject more quickly.
- Manually controlled.
- Autofocus settings.
What does SLR stand for?
Single Lens Reflex.
Describe what is meant by the terms “device dependant” colour space.
- The way in which a device renders information is entirely dependant on the device itself.
- E.g. RGB colours (a device dependant colour space) can be different across different displays or output devices.
- Resultant colours depend on equipment or set up used to process it.
- Will alter if you change the display of your computer for e.g.
What is meant by “device independent” colour space?
- Colour space where colour fidelity and quality will be consistent from one device to another - so independent to any device.
What is a device independent colour space useful for?
- Producing accurate copies and colour matches
- Industry standard
- Transfer across a wider range of devices
Give examples of device independent and dependant colour spaces.
Independent: CIELAB
Dependant: RGB
What advancements have been made in modern digital cameras have been made since the 1975 Kodak prototype?
- Developments of wireless cameras.
- Kodak “Easy Share camera” 2001 - easy to snap pictures then download to a computer.
- 2000: Sharp JSH04 - first digital camera in mobile phone = more portable and accessible to the public.
- 2007: iPhone Camera - shot in different lighting conditions easily.
- Improvements in memory technology.
- Better zoom.
- The Casio QV-10, released in 1995, was the first camera to incorporate an LCD screen on the back that would preview images for the user.
How does the Bayer filter work?
- The Bayer Filter splits the amount of mega pixels available on their sensor into green, red and blue.
- Interprets this information into the information missing from the image.
- Only have some information for each of the pixels - so essentially averages the information from either side.
- Exploits the fact we don’t see colour that well - good luminance makes up for poor colour quality.
What is the Bayer filter?
- A CFA (a colour filter array) that tells the camera how much light has hit a certain position.
- Arranged in a grid format.
- Each position represents a pixel in our image.
- A physical set of elements that intercept certain wave lengths.
Why are there more green elements than red or blue?
- We distinguish luminance much more in the green channel, so more green will look sharper to us - good luminance makes up for poor colour quality.
What is demosaicing?
- Used to determine complete values of green blue and red from a CFA.
- Converts the mosaic into an equally sized mosaic of true colours.
- Each coloured pixel can be used more than once.
- Averaging the values from the closest surrounding pixels.
What is meant by lossy compression?
- Reduces image size by removing parts of the image - can reduce up to 4% of original size.
- Enables greater space saving at the price of losing image detail.
- Redundant information is removed.
- Take advantage of known limitations to the human visual system.
What two statistical properties of image compression might be exploited to reduce data storage?
- Resolution.
- File size.
- Pixels.
What are the differences in acuity in cone and rod cells?
- Cone: High spatial acuity.
- Rod: Low spatial acuity.
What is meant by spatial acuity?
The ability to discriminate fine details of the visual scene.
or
Detection of the shape of a test object. E.g. noticing subtle differences in similar shapes.
Where are colour matches determined?
at CONE level.
How are colours matched?
- People can match any colour using a test stimulus by adjusting the intensity of 3 superimposed light sources generating 3 different lights.
- Match cone response = matching colour.
Provide 2 adaptations of the human visual system in response to the lighting present in the scene.
- Iris: sphincter muscle which allows it to expand or contract - pupils get larger or smaller control amount of light able to enter.
- Retina: contains light sensitive cells that can determine light, dark, colour to assemble images of the world.
What is meant by simultaneous contrast?
When 2 colours are side by side interact with each other and change our perception accordingly.
Apart from copyright describe 2 other types of intellectual property and suggest an example for each.
- Trade mark - symbol used for brands. Word or words legally registered or established by the use of representing a company or product. Can be a sign that identifies you as the owner of your goods or services. E.g. NSB, IBM. E.g. brand names: Apple.
- Patents - used for an invention - protect the function and processes of an object.
What 3 things must an object have in order to qualify for a patent?
- NEW.
- Made or used.
- Inventive - not just a simple modification.
Explain what is meant by copyright and can it be applied to an idea?
- Applies to: music, art, layout, literature, drama.
- Something that can be bought or sold.
- Automatic right.
- Prevents people from knowingly and deliberately copying your work.
- Belongs to the creator.
- Form of intellectual property.
- Ideas cannot be copyrighted - has to be expressed in a material form.
