Computer Graphics:Programming, Problem Solving,

and Visual Communication

Steve CunninghamCalifornia State University Stanislaus and Grinnell College

PowerPoint Instructor’s Resource

Hardcopy

Preserving the results of your graphics work

What kind of hardcopy?

• Who is your audience and how will they be able to see your work?– Digital image (online, presentation, …)

• 2D or stereo viewing?

– Print (article, newsletter, …)– Film (film recorder, …)– Video (online, television, presentation, …)– 3D objects (prototyping, manipulation, …)

• Each can be created directly from your work, but you treat them differently

Digital Images

• Can capture from screen or can use the color buffer capture we described in the code example in this chapter

• The raster (pixel array) these give can then be saved in several file formats

• Each format has advantages and disadvantages

Comparing File Formats

• TIFF– Lossless, often quite large; some compression is

possible (LZW) but optional. If the file is intended to archive your work, this is a very good choice.

• JPEG– Uses a compression technique that is often lossy,

especially if you’re trying to reduce file size. Very good on natural images, but can have serious artifacts on lines and edges. If you want to use jpeg formats, use a commercial tool to create and decode your files.

Comparing File Formats (2)

• GIF– Widely used format for the Web, but it uses the LZW

compression process so it should not be used for commercial work. ((check out color depth))

• Others– PNG

• Gaining acceptance for the Web, no issues with patent or with color depth

– Raw• Simple file with pure RGB components, though some

variations (name?) also include dimensions. Can either be interleaved (rgbrgbrgb…) or not (rrr…ggg…bbb…)

3D Images

• Compute two different 2D images as if each were the view from a single eye

• Present them to the viewer in a way that lets the viewer fuse the images to see a 3D image– manual fusion (side-by-side)– color fusion (anaglyph, Chromadepth™)– temporal fusion (alternate eyes with

polarization)

3D Images - Manual Fusion

• Create two images, one for each eye’s viewpoint• Set the viewpoints carefully to mimic the location

of the eyes• Display the images in side-by-side viewports,

spaced appropriately for the eye to merge them

3D Images - Color Fusion

• Anaglyph process– Create two images, one from each eye’s viewpoint, as in

manual fusion– Compute a new image with the red channel from one view

and the blue and green channels from the other view– View the image through red/blue glasses

3D Images - Color Fusion

• Chromadepth process– Described in the

Textures chapter– Create a grayscale

image– Add a 1D eye-depth

texture that is red near and blue far

– View with diffusion-grating glasses

3D Images - Temporal Fusion

• Compute two images, one from each eye’s viewpoint, as in manual fusion

• Present them alternately through a reversable polarizer, with the user wearing polarized glasses

• CrystalEyes™ is one such technology, described in Chapter 10

Print

• Print involves adapting your images to work with commercial printing techniques.

• Your image must be printed with several single-color components, so it must be separated into these components.

• The most common (and inexpensive) approach is to use the CMYK color model and separations

Print (2) -- separations

• Many commercial tools (e.g. Photoshop) can create CMYK separations for you

Print (3) -- screens

• Once you have your separations, the printer must create screens to control the ink on press; you can’t print one color over another

• Options: traditional screens and stochastic screens, but you should talk to the printer about what can be done

• Stochastic (left) and traditional (right) screens

Film

• Film is not as important as it once was, but it is still a good way to get high-quality images

• Uses a digital film recorder to capture an image one color at a time, using filters

3D Objects

• There are several technologies that are used to create 3D objects from computation

• All rely on the STL file to define 3D objects by specifying the triangles that bound the object

• The file is read to create the boundary of the object at each horizontal level

3D Objects (2)

• The techniques involve creating objects a layer at a time, using– Paper– Wax– Powder– Plastic

• And the objects that are created can be used to understand 3D models more fully

3D Objects (3)

• Four example technologies

LOM System

Z-CorpSystem

ThermaJetSystem

StereolithographySystem