Introduction to digital image compression

Digital image compression, a vital aspect of digital media technology, involves reducing the size of image files through sophisticated encoding techniques while maintaining acceptable visual quality.

Definition of digital image compression

Digital image compression is the process of encoding digital images using fewer bits, thereby reducing their file size for efficient storage and transmission.

Principles of digital image compression

Digital image compression is grounded on two fundamental principles:

1. Pixel correlation: Exploit the redundancy by removing the strong correlation between adjacent pixels within an image.
2. Visual perception: Capitalize on the human visual system’s insensitivity to sharp edge changes and lower resolution to reduce coding accuracy in certain areas.

Technical indicators of image compression

Several key indicators measure the effectiveness of image compression:

1. Compression ratio: The ratio of pre-compression to post-compression bit count per pixel, indicating the degree of compression achieved.
2. Peak signal-to-noise ratio (PSNR): Quantifies the reconstructed image quality relative to the original, calculated as the signal-to-noise power spectrum ratio.
3. Coding efficiency: Reflects how effectively the compression algorithm utilizes bits to represent the compressed image.
4. Redundancy (R): The smaller the redundancy, the less room there is for compression.
5. Average codeword length: Indicates the average number of bits required to represent the compressed image data.

Digital image representation

Digital images are represented in computers as binary data, with color information stored per pixel using color models such as RGB. Binary images, with only two gray levels (0 or 255), are widely used in applications like digital image processing and character extraction.

Compression techniques for binary images

Layer-by-layer coding is an iterative method that decomposes binary images into smaller blocks and encodes them sequentially, enhancing coding efficiency.

Common compression formats

Several common formats for digital image compression include:

• BMP: Uses lossless RLE compression, preserving image quality.
• GIF: Employs a storage format from 1 to 8 bits, widely used for web images.
• JPEG: A fundamental lossy compression format, balancing compression and image quality.
• PSD: Photoshop’s default format, supporting layers and various image adjustments.
• TIFF: Extensive printing format supporting channel saving across platforms.
• PCX: Supports storage from 1 to 24 bits, capable of rich color display.
• TGA: Preferred for converting computer images to TV, with simple structure and lossless compression capabilities.

In summary, digital image compression is essential for managing the vast amounts of data in digital media, balancing compression efficiency with image quality to meet the demands of modern applications.