Image Optimization Glossary

A modern image format based on the AV1 video codec. Offers superior compression compared to JPEG and WebP, typically 50% smaller file sizes while maintaining quality. Supported by most modern browsers.

The proportional relationship between an image's width and height, expressed as width:height (e.g., 16:9, 4:3). Maintaining aspect ratio prevents distortion when resizing images.

An additional channel in an image file that stores transparency information. Used in PNG and WebP formats to create images with transparent backgrounds.

The ability to process multiple images simultaneously with the same settings. Essential for efficiency when working with large numbers of images, such as product photography or web galleries.

The amount of data processed per unit of time in an image or video file. Higher bitrates generally mean higher quality but larger file sizes.

An uncompressed raster image format that stores pixel data directly. Results in large file sizes but perfect quality. Rarely used for web due to size.

The process of reducing image file size by removing redundant data. Can be lossy (removes some data permanently) or lossless (preserves all original data).

Google's metrics for measuring user experience on web pages, including Largest Contentful Paint (LCP). Optimized images significantly improve these scores and SEO rankings.

Software platform for creating and managing digital content. Popular CMS platforms like WordPress benefit greatly from optimized images.

A measure of printing resolution. Standard is 300 DPI for print, 72 DPI for web/screen. Higher DPI means sharper printed images but isn't relevant for digital display.

The width and height of an image measured in pixels. Common web dimensions include 1920×1080 (Full HD), 1280×720 (HD), and various social media specific sizes.

Metadata embedded in image files containing information like camera settings, date taken, GPS location, and copyright. Can be stripped for privacy or kept for organization.

The amount of disk space an image occupies, typically measured in KB or MB. Smaller file sizes load faster but may have reduced quality. Goal is to minimize size while maintaining acceptable quality.

The file type and structure of an image (JPEG, PNG, WebP, etc.). Different formats are optimized for different purposes - photos, graphics, transparency, etc.

An image format supporting animation and limited colors (256). Commonly used for simple animations, but inefficient for photos. Consider WebP or AVIF for better quality and smaller sizes.

Apple's proprietary image format offering better compression than JPEG. Default on iOS devices but limited browser support. Often needs conversion for web use.

The process of reducing image file size while maintaining acceptable quality. Includes compression, resizing, format conversion, and removing unnecessary metadata.

The most common lossy image format, ideal for photographs. Offers good compression and universal support but loses quality with each save. Not suitable for images requiring transparency.

A web optimization technique that defers loading off-screen images until the user scrolls near them. Dramatically improves initial page load speed and Core Web Vitals scores.

Compression that reduces file size without losing any image data. Original quality can be perfectly reconstructed. PNG uses lossless compression.

Compression that permanently removes some image data to achieve smaller file sizes. JPEG and most video codecs use lossy compression. Results in some quality loss.

A Core Web Vitals metric measuring how long it takes for the largest content element to load. Optimized images significantly improve LCP scores.

Information stored within an image file including camera settings, GPS location, copyright, and keywords. Can be preserved or removed during optimization.

One million pixels. A measure of image resolution (e.g., a 12MP camera captures 12 million pixels). Higher megapixels don't always mean better quality - also depends on sensor size and lens.

A lossless image format supporting transparency. Ideal for graphics, logos, and images requiring sharp edges. Larger file sizes than JPEG for photos.

A measure of pixel density on screens. Higher PPI means sharper display. Standard screens are 72 PPI, retina displays are 220+ PPI. Often confused with DPI (for print).

A JPEG variant that loads in multiple passes, showing a low-quality preview that gradually improves. Better user experience on slow connections compared to baseline JPEG.

Images composed of pixels in a grid. JPEG, PNG, WebP, and most photo formats are raster. Quality degrades when scaled up significantly.

The number of pixels in an image, expressed as width × height (e.g., 1920×1080). Higher resolution means more detail but larger file sizes.

Images that adapt to different screen sizes and resolutions. Uses HTML srcset and sizes attributes to serve appropriate image sizes to different devices.

Apple's term for high-density displays with pixel density high enough that individual pixels aren't visible at normal viewing distance. Requires 2x or 3x resolution images for sharp display.

A vector image format that uses mathematical descriptions rather than pixels. Perfect for logos, icons, and illustrations - can scale infinitely without quality loss.

An HTML attribute that specifies multiple image sources for different screen sizes and resolutions. Enables responsive images and improves performance.

A flexible, lossless format popular in professional photography and printing. Supports layers and high bit depths but creates very large files - not suitable for web.

A small, reduced-size version of an image used for previews, galleries, or navigation. Significantly reduces load times when displaying many images.

The ability of an image to have see-through areas. Supported by PNG, WebP, and GIF formats. Essential for logos and graphics that need to blend with backgrounds.

Images defined by mathematical paths rather than pixels. SVG is the primary web vector format. Can scale to any size without quality loss - ideal for logos and icons.

Google's modern image format offering superior compression compared to JPEG and PNG. Supports both lossy and lossless compression, plus transparency and animation. Widely supported by modern browsers.

A visible overlay (usually logo or text) added to images to indicate ownership or copyright. Can deter unauthorized use of images.