INTRODUCTION TO DIGITAL IMAGES

Intro to digital images

Steps of Digital Photography

• Step 1. Capturing Photographs (from Digital, film, slides, negative,etc)

• Step 2. Editing Photographs (using photo-editing program such as Photoshop)

• Step 3. Sharing Photographs (Print, e-mail, web, DVD,etc)

GRAPHIC QUALITY

• Two factors that determine image quality are resolution and color depth.

– Resolution is the number of pixels per inch.

– Color depth refers to the number of distinct colors an image can contain.

- Image quality also dependent upon the equipment on which they are produced (scanner, camera) or displayed (monitor, graphics card)

RESOLUTION

• affects the amount of discernible fine detail in an image.

• Computer images are made of dots.

• The more dots per inch (dpi), the higher the resolution.

Used when printing - pixels are turned into dots per inch and counted by the spread over the paper. Printers range from 300 dpi to 2400 dpi(or more).

• On the computer screen, the dots are called pixels.

• Monitor resolution is usually around 72 –96 dpi.

The color depth determined “How much data in bits used to determined the number of colours in an image file”. Colour depth is measured in bits per Pixel

Colour Depth

– 1 bit

– 8 bit

– 16 bit

– 24 bit

– 32 bit

The greater the color depth, the more colors may be stored.

For example:

– 1 bit 2 colors

– 8 bit 256 colors

– 16 bit 65,536 colors

– 24 bit 16.7 million colors

– 32 bit Millions plus extra information

The greater the color depth, the more colors may be stored.

For example:

– 1 bit 21 2 colors

– 8 bit 28 256 colors

– 16 bit 216 65,536 colors

– 24 bit 224 16.7 million colors

– 32 bit 232 Millions plus extra information

• The more colors per pixel, the larger the file size.The higher the image resolution the greater the file size. The higher color depth, the greater the file size.

File size vs Resolution vs Colour depth ?

• The more colors used, the more bytes are required to encode the image, and the more bytes required for an image, the larger the file to store the image.

• The higher the image resolution the greater the file size.

GRAPHIC FILE FORMATS

• Some of the most common are:

– GIF (Graphics Interchange Format)

– JPEG (Joint Photographic Experts Group)

– TIFF (Tagged Information File Format)

– PIC (PICTure)

– BMP (bitmap)

– TGA (Targa)

– PNG (Portable Network Graphics)

Which file format should be used:

• Small images like icons and buttons: GIF or PNG

• Line art, grayscale (black and white), cartoons: GIF or PNG

• 24-bit color-depth lossless Image: PNG, JPG

• Scanned images and photographs: JPG

• Large images or images with a lot of detail: JPG

• Animated icons : GIF

• High Quality printing: TIFF

TIFF or TIF

• Good for master copies of images.

• Uses lossless compression which means when a TIFF file is saved, no image

information is thrown out.

• This also means the files can be large. JPEG or JPG

• JPG is the most common format for viewing images on the Web.

• JPEG images are small for fast delivery over the Web and are also the most

common format saved in digital cameras. JPEG or JPG

• JPEG uses lossy compression

• Don't save JPG's over and over because the images get compressed over each

other and lose significant amounts of image detail and information.

• High quality JPEG is often 1/10 the size of a TIFF.