Image Manipulation

• Any creative activity involving specialized software for which the end result is a digital image.
• Usually it involves image generation, editing, and/or processing.
• Image generation - scanning, digital photography, digital painting/drawing, rendering of a 3D model.
• Image editing - alteration, enhancement, special effects.
• Image processing - modifications applying methods from signal processing, filters, transformations.

Digital Image

• A digital image is a representation of a two-dimensional image as a matrix of digital values, called picture elements or pixels.
• Representation: the image is usually stored in a file allowing a specialized program to redisplay all the pixels in the right order.
• File formats: several categories based on the image being compressed/uncompressed, and the compression being lossy or lossless.

Digital Image Representation

• Digital image : a matrix of pixels.
• Pixel: picture element, unit for screen and digital images.

Image Properties

• Resolution: pixel density.
• Screen: 1024x768
• Printer 300 dpi (dots per inch)
• Picture: 76 dpi
• Pixel encoding:

  B/W: 1 bit/pixel

  16 colors: 4 bits/pixel

  256 colors or grays: 8 bits/pixel

  True color: 32 bits/pixel

Color Models

• RGB: red, green, blue
  [0, 1] [0, 1] [0, 1] or [0, 255] [0, 255] [0, 255]
• CMY: cyan, magenta, yellow - printer
  [0, 1] [0, 1] [0, 1]
  (C, M, Y) = (1, 1, 1) - (R, G, B)
• HSV: hue, saturation, value - image processing programs
  [0, 359] [0, 1] [0, 1]

Classification of Digital Images

• Vector:

  set of primitives like lines, rectangles, spheres, etc., specified with coordinates and dimensions

  xfig, Inkscape, ClarisDraw, PowerPoint, Clip Art, etc.

  high level of compression, easy editing, looks good in any size

  shape restrictions

• Bitmap or raster:

  set of individual pixels

  direct RGB / lookup table or color map

  true color / 256 colors or grayscale

Images Formats

• JPEG (Joint Photographic Experts Group) true color, lossy compression.
• GIF (Graphics Interchange Format) 256, lookup table, transparency, supports layers for animation
• PNG (Portable Network Graphics) 256, multiple levels of transparency
• BMP (Windows bitmap) 2-true
• TIFF (Tagged Image File Format) true, lossless compression
• TGA (Targa File, SUN) true
• EPS (Encapsulated PostScript) true

Digital Painting

• An image creation technique in which the painting is achieved directly using digital tools.
• The pen/pencil/brush are replaced by the use of the mouse and the tablet stylus.
• Advantages: easy editing, undo, various available brush types and effects; layered images offer better control of the content.
• Examples:
  http://www.deviantart.com/deviation/46740938/
  http://flowerzzxu.deviantart.com/art/Silent-Valley-I-97372646
  http://www.deviantart.com/deviation/46752564/

Common Painting Tools

• Pen - draws hard edges strokes.
• Brush - draws soft edged strokes.
• Fill - fills an entire area continuous with a color.
• Erase - deletes part of the image.
• Region - selects part of the image so that the editing only affects the selected region.

Software

• Paint - simplest program, available by default. Example.
• The Gimp - the GNU Image Manipulation Program, multi-platform, open source, big community of users and developers.
• Adobe Photoshop - very popular, commercial software.
• Commercial - Macromedia FreeHand & Director, Claris Draw, Corel Paint
• Free - Google Picasa, PhotoFiltre, Artizen ZE, Tux Paint, Inkscape (vector).

Rendering

• An image creation process that consists in generating an image starting from a model (most often 3D).
• Rendering in the Gimp:
• main window, Xtns menu, Script-FU
• image window, Filters menu, Render
• Scene-based rendering - the image is created from a scene containing a description of a set of geometric objects.
• Procedural rendering - the image is created from a function (fractals). This can be used as a texture for the scene-based rendering.