The Digital Image
McMaster University, Faculty of Humanities
image pixel pushers exhibition
Dr. Lori Shyba
Dada and Photomontage
• In the 1920s The Berlin Dadaists
- the monteurs (mechanics) -
would use scissors and glue
rather than paintbrushes and
paints to express their views of
modern life through images
presented by the media. A
variation on the collage
utilized actual or reproductions
El Lissitzky The Constructor, a self-portrait photomontage, c.1925
of real photographs printed in
Dada, a description
Dada is the groundwork to
abstract art and sound poetry,
a starting point for
performance art, a prelude to
postmodernism, an influence
on pop art, a celebration of
antiart to be later embraced for
anarcho-political uses in the
1960s and the movement that
lay the foundation for
George Grosz, c.1925
Fernand Leger 1881-1955
• Leger juxtaposed natural
forms and mechanical
elements exemplifying what
he called the “law of contrast.”
• In 1924, in collaboration with
George Antheil, and Man Ray,
Léger produced and directed
the iconic and Futurism-
influenced film, Ballet
Mécanique. (See wiki,
“January 2009” page for
Part 2, The Week’s reading, from Spalter, Digital Painting and Photoediting
2-D Raster Graphics
• In computer graphics, a raster graphic image or
bitmap, is a data structure representing a generally
rectangular grid of pixels, or points of color,
viewable via a monitor, paper, or other display
• Raster graphics are resolution dependent. They
cannot scale to an arbitrary resolution without loss
of apparent quality.
• More commonly, we create 2-D graphics in
Discreet Digital vs Continuous Analog
• If colours in an image are discrete, one can assign
numbers to each colour element, encoding the
information in a digital format. A simplified
example of this is cross-stitch needlepoint.
• If colours are continuous, there is always another
colour between any two points of colour. In
analog method, a continuous physical process
translates changes in one medium into changes in
See figure 2.6, Page 2
Sampling Analog to Digital
• Analog images are digitized by reducing their
continuously varying values and colours to
discrete quantities based on measurements or
samples taken at equal spatial intervals.
• The science of sampling depends on the
frequency of the samples (how many are taken
per inch), the way the samples are calculated, and
the way the sample information is used to recreate
See figure 2.8, Page 4
• An image pixel is a point sample, the value of a
continuous thing at a single point. (Alvy Smith,
creator of the “Paint” program.)
• A screen pixel is the smallest area that a particular
combination of software and hardware can
illuminate on a monitor.
• When a document is viewed at 100% scale, each
image pixel is represented by a screen pixel.
When viewed at > 100%, each image pixel is
represented by several screen pixels.
Local-Touch Mark Making
• Touch is the artist’s experience of making a mark in
the process of creation.
• Local-touch mark making is controlled by hand
accumulating over time of small marks to make large
image. Compares to traditional charcoal etc.
• The artist observes and records and makes new
marks based on the appearance of all the marks
accumulated up to that time. EG. Haiku assignment.
See figure 2.14, Page 10
Global-Touch Mark Making
• Global-Touch tools change an entire image area
simultaneously, for eg. scaling, rotating, replacing
one colour with another.
• Global process, or “algorithmic” processes, are
common on the computer but rare in traditional
• The hand plays almost no role and changes made
to the image affect the whole piece or a
• On the computer, an artist makes tonal changes by
taking a pixel’s sample colour value and mapping
it to a new sample value by performing some
preset operation. Examples.
• Changes a pixel’s value by averaging the
brightnesses of neighbourhoods of pixels.
• Tonal mapping and filtering map old pixels values to new ones.
• Whereas tonal mapping and filtering map old
pixels values to new ones, transformations map
pixel values to new locations within the image.
Selection and Masking
• When using global-touch tools, one must
differentiate a selected region from other areas.
• Selection is the opposite of the traditional practice
• Cloning tools use as a source a reference point on
one image and copy pixels to another area in the
same or a different image.
• Composition of a piece is its structure (plus aesthetics),
the overall arrangement of form and colour. This space
may be representational or abstract, illustionistic or
iconographic; whatever the logic or artistic inspiration
there are strategies for structure (and aesthetics).
Image Size, File Size, Resolution
• Read pages 30 and 31 again because it is crucial.
• The size of a raster graphic image is its file size or
the amount of information needed to describe the
• File size can also be thought of as the amount of disk
space necessary to store the file (not taking
compression into consideration.
• File size is determined by the image’s dimensions,
(height and width), resolution, (number of pixels per
inch), and colour depth (number of colour choices
Image Size, File Size, Resolution
• Number of pixels in image =
(height x width) x resolution
• The minimum number of choices for colouring an
image is two. This is a 1-bit image or bitmap.
• 2-bits can describe four different colours.
• 3-bits can describe 8 difference colurs.
• 8- bits can describe 256 different colours that is:
See figure 2.34, Page 33
• Scaling is often referred to as resampling because the
number of samples (pixels) change.
• When an mage is scaled, it deteriorates somewhat.
New pixels based on guesswork are introduced when
the user sales up, and some info is always discarded
when scaling down.
See figure 2.35, Page 36
The Alpha or Transparency Channel
• Read pages 38 and 39 because it is crucial.
• Transparency (also referred to as opacity) is a
powerful tool for creating space in 2D art.
• Samples associated with a single pixel are stored in
channels which can be manipulated separately.
• RGB has red green blue channels. CMYK has cyan
magenta yellow black channels.
• Alpha channels calculate transparency for the
fraction of colour that will show through on the final
• Ways of introducing alpha channels include
masking, eraser tool, feathering, graduated fills.
• Grey values in an alpha channel represent partial
• Alpha channels are vital in compositing, or the
merging of images with varying levels of
• (This is crucial for the next assignment.)
See figure 2.38, Page 40