Digital Darkroom I

1
Digital Darkroom I

• Theresa L. Ford

2
Objectives

• Basic Digital Image Terminology
• Screen Display of Pictures
• Why are pictures too big for the screen?
• Why cant I send/receive a picture over email?
• Software Demos

3
Hardware Requirements

• Add RAM memory - the larger the file size you are
  working with, the more you need.
• Adobe Photoshop CS2 requires a Pentium 3 or 4
  equivalent processor, 320 Mb of RAM, 650 Mb of
  disk space, 1024x768 monitor resolution with a 16
  bit video card. Thats techie for if the
  computer is over 2 years old, youll likely have
  problems.

4
Getting a Digital Image

• Scanner
• For printing, scan at highest resolution.
• Digital Camera
• For the best print options, set the camera to
  save the largest file size (maximum resolution).
• Unfortunately, this means you cant take as many
  pictures per disk.

5
What is a Digital Image?

• Tiny squares of color called dots or pixels saved
  as data in computer files.

6
Describing a Digital Image

• File Type - how the pixel data is stored
• Image Size - width and height in pixels
• File Size - space used to store data in bytes
• Color Depth - how many colors
• Color Space - which colors
• Resolution - ?

7
File Types

• RAW - Camera sensor data, stored in a vendor
  specific format
• Canon RAW is not the same as Nikon RAW
• Requires special support in picture editing
  programs
• TIF/TIFF - Tagged Image File Format
• Many file variations to handle many options
• Typically used for lossless image data storage
• JPG/JPEG - Joint Photographic Experts Group
• Lossy compression creates smaller file sizes
• GIF, BMP, PICT, PNG

8
Image Size
9
Resolution ?

• Total number of pixels - approximately - from the
  camera specs (2.1 megapixels)
• Image size - pixel width by pixel height
  (800x600)
• Pixel density - pixels per inch (PPI) (72 PPI)
• Printer ink drop density - dots per inch (DPI)
  (2880 x 1440 DPI)
• Display setting on monitor - pixel width by pixel
  height (1024x768)

10
More Definitions of Resolution

• Color depth - number of available colors on the
  monitor (4294967295 - 32 bit - true color)
• Number of available colors in the image file (8
  bit/16 bit)
• What you intend to do in 2006

11
DPI and PPI

• Often used interchangeably (though inaccurately).
• DPI usually refers to printers - the more dots of
  ink (CMYK) per inch, the better the print
  quality.
• PPI usually refers to the viewed image size
  (print) - the number of pixels or dots in a
  displayed inch.
• A computer screen displays 72 pixels per inch at
  100.
• A 800x600 (pixel width by pixel height) image can
  be saved with any PPI.

12
File Size and the Internet

• Most email clients block attachments over 2Mb.
• 2Mb takes a long time to download over 56Kb
  (modem).
• A 4x6 print scanned at 584 PPI is 5Mb.

For happiest internet file sharing, crush the
file to its smallest size with acceptable image
quality.
13
Optimizing for the Web

• Step 1 - Copy files (never work with originals)
• Step 2 - Edit composition (if you must)
• Step 3 - Shrink to desired image size
• Step 4 - Sharpen
• Step 5 - Shrink to the smallest file size without
  losing quality

14
Some Graphics Software

• Photoshop CS
• The Gimp
• Paint Shop Pro
• XAT.coms optimizers
• ImageMagick
• Picasa
• Irfanview

15
A Little Math

• Pixels / PPI Print Size at 100
• Pixels / 72 Screen Size at 100

For best print quality, use the highest PPI
possible to a maximum of the printers ability.
16
A Little More Math

• To make an 8x10 print at 300 PPI
• 8 x 300 PPI 2400 Pixels
• 10 x 300 PPI 3000 Pixels
• To make a 800x600 Desktop Background
• 800 Pixels
• 600 Pixels
• PPI is irrelevant