Digital Darkroom I

Theresa L. Ford

Objectives

• Basic Digital Image Terminology• Screen Display of Pictures

– Why are pictures too big for the screen?

– Why can’t I send/receive a picture over email?

• Software Demos

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. That’s techie for “if the computer is over 2 years old, you’ll likely have problems”.

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 can’t take as many pictures per disk.

What is a Digital Image?

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

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” - ?

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

Image Size

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)

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

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.

File Size and the Internet

• Most email clients block attachments over 2Mb.

• 2Mb takes a long time to download over 56Kb (modem).

• A 4”x6” print scanned at 584 PPI is 5Mb.

For happiest internet file sharing, crush the file to it’s smallest size with acceptable image quality.

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

Some Graphics Software

• Photoshop CS• The Gimp• Paint Shop Pro • XAT.com’s optimizers• ImageMagick• Picasa• Irfanview

A Little Math

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

Pixels PPI Print Screen

72 72 1.0 1.0600 72 8.3 8.3800 300 2.7 11.11200 300 4.0 16.71800 300 6.0 25.02400 300 8.0 33.33000 300 10.0 41.72336 300 7.8 32.43504 300 11.7 48.72336 584 4.0 32.43504 584 6.0 48.7

Inches

For best print quality, use the highest PPI possible to a maximum of the printer’s ability.

A Little More Math

• To make an 8”x10” 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