Image formats

Basic terminologies…

• Pixels: Pixels are the building blocks of every digital image . • a pixel is a single point in a graphic image.

• Resolutions: We measure resolution in pixels per inch or more commonly, dots per inch (dpi).

• Resolution is the number of pixels per inch (or PPI), but it is most commonly referred to as dots per inch (DPI).

• The more pixels, or “dots,” per inch, the higher your image resolution will be.

Memory cost of images• Large images consume large memory and make our computers

struggle. Memory cost for an image is computed from the image size.

• For a 6x4 inch image at 150 dpi, the image size is calculated as:   (6 inches × 150 dpi) × (4 inches × 150 dpi) = 900 × 600 pixels • 900 × 600 pixels is 900 × 600 = 540,000 pixels. • The memory cost for this RGB color image is: •   900 × 600 × 3 = 1.6 million bytes. • The last "× 3" is for 3 bytes of RGB color information per pixel for 24

bit color (3 RGB values per pixel, one 8-bit byte for each RGB value, which totals 24 bit color).

• Assume 240 dpi is fine for our needs. 240 dpi means, there are 240 distinct pixels. Multiply 5" X 240 = 1,200 pixels. 7" X 240 = 1,680 pixels. Total number of pixels is width X length or 2,016,000 pixels.

• Mega is the short prefix for million... this is a 2 megapixel camera

• Here's a chart to help get you started:• Resolution                      Max picture size w/interpolation• 640 x 480 (.3 mp)                               3" x 4"• 960 x 1200 (1.1 mp)                           5" x 7"• 1300 x 1600 (2 mp)                            8" x 10"• 1600 x 2000 (3 mp)                      9 1/2" X 11 1/2"• 2100 x 3100 (6.2 mp)                  12 1/2" x 18 1/2"

Basic image formatsImage file compression There are two types of image file compression algorithms: lossless

and loss.Lossless compression :algorithms reduce file size without losing

image quality, though they are not compressed into as small a file as a lossy compression file. When image quality is valued above file size, lossless algorithms are typically chosen.

Lossy compression :algorithms take advantage of the inherent limitations of the human eye and discard invisible information.

Image formats.• BMP: (bitmap)

• TIFF: (Tagged Image File Format)

• PNG:(Portable Network Graphics)• GIF: (Graphics Interchange Format )

• JPEG: (Joint Photographic Experts Group )

FORMAT NAME CHARACTERISTICS

BMP Windows bitmap Uncompressed format

TIFF Tagged Image File Format Lossless: Document scanning and

imaging format. Flexible

GIF Graphics Interchange Format

LOSSLESS: captures very limited color

PNG Portable Network Graphics Lossless: improve and replace GIF..

JPEG Joint Photographic ExpertsGroup

Lossy: big compression ratio, good for

photographic images

• 1 bit (binary digit) = the value of 0 or 1

• 8 bits = 1 byte

• 1024 bytes = 1 kilobyte

• 1024 kilobytes = 1 megabyte

• 1024 megabytes = 1 gigabyte

• 1024 gigabytes = 1 terabyte

• 1024 terabytes = 1 petabyte