Image File Formats and Digital Imaging Concepts

Image File Formats

• Image file formats are used to store digital images.
• Common image file formats include JPEG, PNG, GIF, TIFF, PSD, and RAW.
• Other formats include XCF, BMP, and TGA.
• Vector formats include AI, CDR, and SVG.
• EPS and PDF are also used for final delivery.

Key Digital Imaging Concepts

• Raster graphics use a grid of pixels (bitmap).
• Vector graphics use geometric formulas.
• Lossy compression reduces image quality to reduce file size.
• Lossless compression preserves image quality.
• Colour spaces, bit depth, and alpha channels affect image quality and file size.

Reducing File Size

• Most raster formats use some form of compression.
• Lossy compression discards data, reducing image quality using the Discrete Cosine Transform (DCT).
• Non-lossy compression retains all information.
• Run-length encoding (RLE) is an example of non-lossy compression.

Colour Channels

• Most image formats store data in three colour channels using the RGB colour space (red, green, blue).
• Some formats also store data in four colour channels (CMYK - cyan, magenta, yellow, black).
• Some image formats store data in a single black and white (grayscale) channel.

Bit Depth & Alpha Channels

• Most formats support 8 bits per channel (8bpc).
• A three-channel RGB colour space delivers 24-bit colour.
• Some formats support 16bpc and 32bpc.
• Others may use 8-bit colour to reduce file size.
• Some formats store pixel transparency in an alpha channel (e.g., RGB becomes RGBA).

JPEG

• Created by the Joint Photographic Experts Group in 1992.
• Uses lossy compression (DCT).
• Stores raster images in RGB or CMYK color.
• Supported color depth is limited to 24-bit.
• Suitable for photographs but not ideal for print workflows.

PNG

• Portable Network Graphics; created in 1994.
• Uses non-lossy compression.
• Can include an alpha channel.
• Supports 8-bit or 24-bit colour (no CMYK).
• PNG8 uses 8-bit color, PNG24 uses 24-bit color.
• PNG32 includes the alpha channel (RGBA).

GIF

• Graphics Interchange Format, created by Compuserve in 1987.
• Stores raster images using non-lossy compression.
• Maximum file size is limited to 8-bit color (256 colors).
• Useful for web graphics, including animations.

TIFF

• Tagged Image File Format; released in 1986 and last updated in 2002.
• Can use no compression, lossy, or lossless compression.
• Supports RGB, CMYK, and grayscale.
• Includes an alpha channel.
• Supported color depth of 8, 16, or 32 bits per channel.

PSD

• Photoshop Document; the native Adobe Photoshop file format.
• Stores mainly non-compressed raster images.
• Can include vector data like text and other elements.
• Supports RGB, CMYK, and grayscale.
• Stores data in 8, 16, and 32 bits per channel.
• Based on layers. Each layer includes an alpha channel.

RAW

• A native raster format for digital cameras.
• Stores the sensor's raw data, color depth varies between 12, 14, or 16 bits per channel.
• Raw files are captured directly from camera sensors.
• Panasonic, Leica, and Casio often use the RAW format.
• Common file extensions for raw files include .nef, .cr2, .arw, .dng.

Other Raster Formats

• XCF is the native GIMP format
• BMP is a Microsoft bitmap format.
• TGA is a Truevision Targa format.

Vector Image Formats

• Store images mathematically (geometric formulas).
• AI (Adobe Illustrator) is a dominant vector format.
• CDR is a CorelDRAW file format.
• SVG (Scalable Vector Graphics) is an open standard.

EPS & PDF

• EPS (Encapsulated PostScript) and PDF (Portable Document Format) are largely vector based.
• Used for final delivery.
• Raster images can be embedded in both formats.

This quiz covers essential image file formats such as JPEG, PNG, and GIF, along with key concepts in digital imaging including raster vs. vector graphics, compression methods, and color channels. Test your knowledge on how these elements affect image quality and storage efficiency.