Photoshop
Digital Graphics
Review Answers
Answers
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What colour space is used for digital graphics?
RGB. -
Explain the major differences between a bitmap graphic and a vector graphic?
Bitmaps: resolution-dependent, images are formed using pixels, resizing causes image quality to deteriorate.
Vector: resolution-independent, images are formed using mathematical formulae, resizing has no effect on quality. -
What image resolution would a digital graphic require on a Web site typically? Why?
Usually 72 ppi but anywhere between 72 ppi and 96 ppi. The resolution of computer monitors falls within this range, depending on the screen size. -
Why would a JPEG file format be chosen instead of a GIF file format?
JPEGs are most suitable for images containing many colours, such as a photograph because they can support millions of colours. GIFs, on the other hand, support a maximum of 256 colours and so are better suited to images with few colours such as logos and simple illustrations. -
What is a pixel?
Pixel is short for picture element. A pixel is made up of a triad of red, green, and blue phosphors. -
What determines the size that an image will display on a computer monitor?
Screen resolution and image dimensions. -
What does the term 'resolution-dependent' mean?
One image pixel needs one monitor pixel to display it. The size that an image will display is dependent on the monitor's resolution setting. -
Give some examples of bitmap file formats.
GIF, JPEG, PNG, PSD (Photoshop), TIFF, and BMP. -
How is digital image resolution measured?
In ppi, or pixels per inch. -
Will the resolution of an image affect its file size when it has been saved in a format compatible with displaying on the Web?
No. -
What is a colour space?
A colour space defines a colour model with a specific range of colour (also known as gamut) that can be expressed in different ways, depending on how the colour is to be used. -
What is gamut?
The range of colour a device can produce, or the range of colour a colour model can represent. -
Describe the RGB colour space.
The RGB colour space defines the amount of red, green, and blue that will be used to create a colour. The RGB colour space is used for describing colour for monitors. -
What characteristic determines how many colours an image can contain?
Colour depth. -
What are the three bitmap formats supported for use on the Web?
JPEG, GIF and PNG (partially). -
Name some of the features supported by the GIF89a format.
Lossless compression, interlacing, transparency, animation. -
Which image format would be the most suitable for images containing areas of solid colour and with few colours, such as logos, cartoons and buttons?
GIF. -
What bit depth do JPEG images have and how many colours are supported?
24-bit, 16.8 million colours. -
Which bitmap format(s) for use on the Web support transparency?
GIF, PNG. -
Describe the vector image format.
Resolution-independent, are rendered using mathematical formulae rather than pixels, can be scaled with no loss in quality.
Bonus Answers
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Can you name other colour spaces and identify the differences between them and the RGB colour space?
CMYK is used for print and is based on a subtractive colour model whereas RGB uses an additive colour model. -
What compression scheme is used in the TIFF file format?
LZW compression, which is lossless. -
Would the PNG file format be better than a JPEG or GIF file format? Describe why.
Not for use on the Web. PNG browser support is still spotty so some viewers may not be able to see PNG images. -
What three elements must be present in order to see colour?
Light, an illuminated object, and an observer.
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