McMaster University, Faculty of Humanities

The Digital Image

Dr. Lori Shybawww.sundialmedia.comE-mail: shybal@mcmaster.ca

image pixel pushers exhibition

http://www.youtube.com/watch?v=V9Jo0BRdbO4

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 technique, photomontage utilized actual or reproductions of real photographs printed in the press.

Part 1

El Lissitzky The Constructor, a self-portrait photomontage, c.1925

Dada, a descriptionDada 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 Surrealism.

-Marc LowenthalGeorge 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 Youtube link.)

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 medium.

• 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 Adobe Photoshop.

Part 2, The Week’s reading, from Spalter, Digital Painting and Photoediting

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 another.

See figure 2.6, Page 2

Navajo Rug

Discreet Image

Photographcredit: Yuri Dojc

Continuous Image

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 the image.

See figure 2.8, Page 4

The Pixel

• 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 art work.

• The hand plays almost no role and changes made to the image affect the whole piece or a predetermined area.

HALFTIMEENTERTAINMENT!

http://www.youtube.com/watch?v=yhKKIXDypxk&feature=related

Tonal Mapping

• 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.

Filtering

• Changes a pixel’s value by averaging the brightnesses of neighbourhoods of pixels. Examples.

• Tonal mapping and filtering map old pixels values to new ones.

Transformations

• 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 of “masking.”

Local-Global Continuum• 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

• 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 image.

• 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 per pixel.)

Image Size, File Size, Resolution

• Number of pixels in image = (height x width) x resolution

Colour Depth

• 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:2x2x2x2x2x2x2x2.

See figure 2.34, Page 33

Scale

• 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 image.

Alpha/Transparency Continued

• Ways of introducing alpha channels include masking, eraser tool, feathering, graduated fills.

• Grey values in an alpha channel represent partial transparency (opacity).

• Alpha channels are vital in compositing, or the merging of images with varying levels of transparency.

• (This is crucial for the next assignment.)

See figure 2.38, Page 40