Reference

Image Glossary

Plain-English definitions of image format, compression, and resizing terms. Use these definitions to make informed decisions about your images.

A

Above the fold #: The visible portion of a webpage before scrolling, critical for image loading and web performance.
Algorithmic reach #: The number of accounts a social media algorithm distributes content to based on engagement predictions.
Alpha channel #: The alpha channel stores transparency information in digital images, determining how see-through each pixel appears.
Alt text #: A text description in HTML that makes images accessible to screen readers and search engines.
Anti-aliasing #: Anti-aliasing smooths jagged edges in digital images by blending edge pixels with background colors.
Aspect ratio #: The proportional relationship between an image's width and height, expressed as a ratio like 16:9 or 4:3.
AVIF #: AVIF is a modern image format that creates files 50% smaller than JPEG with identical visual quality.

B

Base64 encoding #: Base64 encoding converts binary image data into text characters for transmission through text-only systems.
Batch processing #: Processing multiple images simultaneously with identical settings applied to every file automatically.
Bit depth #: Bit depth determines how many color shades each pixel channel can display, directly affecting image smoothness and quality.
Blocking artifact #: Visible rectangular grid patterns in compressed images caused by JPEG's 8×8 pixel block compression method.
Bounce rate #: The percentage of visitors who leave your website after viewing only one page.
Browser support #: Browser support measures the percentage of web browsers that can natively display specific image formats without plugins.

C

Carousel post #: A social media post format containing multiple images or slides that viewers swipe through horizontally.
Center crop #: Center crop preserves the geometric center of an image while removing equal amounts from opposite edges.
Chroma subsampling #: A compression technique that reduces color data resolution while preserving brightness detail to minimize file size.
Click-through rate (CTR)#: Click-through rate (CTR) measures how many people click your content after seeing it displayed.
Client-side processing #: Image processing that runs entirely in your browser without uploading files to any server.
CLS (Cumulative Layout Shift)#: CLS (Cumulative Layout Shift) measures how much webpage content unexpectedly moves during loading, damaging user experience.
Codec #: A codec is software or hardware that compresses and decompresses image data for storage and viewing.
Color banding #: Color banding creates visible steps in smooth gradients when compression reduces available colors.
Color profile #: A color profile tells devices how to display colors in an image file correctly.
Color space #: A standardized system that defines the range of colors an image can display and reproduce.
Compression #: Image compression reduces file size by encoding visual data more efficiently without changing pixel dimensions.
Compression artifact #: Visible distortions in images caused by lossy compression discarding data to reduce file size.
Content negotiation #: A server technology that automatically delivers the best image format each browser supports without changing HTML.
Core Web Vitals #: Google's user experience metrics that measure page speed and directly impact search rankings.
Cover photo #: A cover photo is the large banner image displayed at the top of social media profiles.
Crop #: Image cropping removes outer edges to change dimensions and aspect ratio without scaling content.

D

Double compression #: The cumulative quality degradation that occurs when a lossy-compressed image undergoes compression multiple times.
DPI / PPI #: DPI measures print resolution while PPI measures screen resolution — understanding both ensures proper image quality.

E

Encoding speed #: Encoding speed is how long it takes software to compress an image into a specific format.
EXIF data #: EXIF data is hidden metadata in photos that reveals your location, camera, and personal information.

F

Favicon #: A favicon is the small square icon displayed in browser tabs and bookmarks that identifies your website.
fetchpriority #: An HTML attribute that tells browsers to download critical images before other resources.
File naming #: The practice of giving images descriptive, SEO-friendly names that help search engines understand and rank your content.
File size #: Image file size is the amount of storage space a digital image occupies, measured in KB or MB.
For You Page (FYP)#: TikTok's algorithmically curated discovery feed that surfaces content based on predicted interest rather than follower relationships.
Format #: Image format determines how your photo is encoded, compressed, and stored as a digital file.
Format compatibility #: Format compatibility determines whether image files open, upload, and display correctly across different devices, browsers, and platforms.

G

Generation loss #: The cumulative quality degradation that occurs when editing and resaving lossy-compressed images multiple times.
Geotag #: A geotag is GPS location data automatically embedded in photo EXIF metadata when captured.
GIF #: GIF is a legacy image format that supports animation but is limited to 256 colors.

H

HDR / High Dynamic Range #: HDR images capture far greater brightness ranges than standard images, from deepest shadows to brightest highlights.
HEIC / HEIF #: Apple's space-saving photo format that stores images at half the file size of JPEG with equivalent quality.
Hero image #: A hero image is the large, prominent image at the top of a webpage that loads first and impacts search rankings.

I

Image CDN #: A specialized content delivery network that automatically optimizes and transforms images for each visitor's browser.
Image optimization #: Image optimization reduces file sizes and improves metadata to make websites load faster and rank higher.
Image SEO #: The practice of optimizing images and metadata to rank higher in Google Images and search results.
Image sitemap #: An XML file that lists image URLs for Google to discover and index images missed by standard crawling.
Interpolation #: The mathematical process that estimates new pixel values when enlarging images beyond their original dimensions.
IPTC data #: IPTC data is professional metadata that photographers manually add to images for copyright and cataloging purposes.

J

JPEG / JPG #: JPEG is the most widely supported photographic image format that uses lossy compression to reduce file sizes.

L

Lazy loading #: A web performance technique that defers loading off-screen images until users scroll near them.
LCP (Largest Contentful Paint)#: LCP measures how long your page's largest visible element takes to load completely.
Letterboxing #: Letterboxing creates black bars around images when aspect ratios don't match display containers.
Link preview #: A link preview is the automatically generated card with image, title, and description that appears when sharing URLs on social platforms.
Lossless compression #: Lossless compression reduces file size without permanently losing any image data or quality.
Lossless conversion #: Converting between image formats while preserving every pixel exactly as it was in the original.
Lossy compression #: Compression that permanently removes image data to reduce file sizes by 60-80%.

M

Megapixel #: A megapixel equals one million pixels and determines an image's maximum resolution and print size.
Metadata #: Image metadata is hidden information embedded in photo files including camera settings, location data, and color profiles.
Mobile-first #: Mobile-first design prioritizes smartphone screens before desktop, reflecting how most social media content is consumed today.

O

Open Graph image #: The image that displays in social media preview cards when sharing website links.

P

Page weight #: Page weight is the total file size of all resources a browser downloads to display a web page.
Perceptual quality #: Perceptual quality measures how closely a compressed image matches the original as judged by human vision.
Picture element #: An HTML element that serves different image formats and crops to different browsers and screen sizes.
Pixel #: A pixel is the smallest unit of a digital image, representing one point of color.
Pixel dimensions #: The width and height of an image measured in pixels that determine display size and quality.
Platform compression #: Platform compression is the automatic re-encoding that social media platforms apply to every uploaded image.
PNG #: PNG is a lossless image format that preserves perfect quality and supports transparent backgrounds.
Profile grid #: The mosaic display of Instagram posts that switched from square to 3:4 format in January 2025.
Profile photo #: A profile photo is the square image uploaded to social accounts that displays as a circle across all platforms.
Progressive JPEG #: Progressive JPEG encodes image data in multiple quality scans for faster perceived loading on slow connections.
Proportional scaling #: Proportional scaling resizes images while maintaining their original aspect ratio to prevent distortion.

Q

Quality setting #: A numerical parameter that controls how much lossy compression is applied to an image.
Quantization #: The JPEG compression step that permanently discards image data by rounding frequency coefficients to reduce file size.

R

Raster image / Vector image #: The two fundamental digital image types: raster images use pixel grids, vector images use mathematical shapes.
RAW #: RAW image format stores unprocessed camera sensor data with maximum editing flexibility and image quality.
Resize #: Image resizing changes pixel dimensions to make images larger or smaller while preserving all content.
Resolution #: Image resolution refers to the number of pixels in an image, measured differently for screen display versus print output.
Retina display / HiDPI #: A retina display is a high-density screen where individual pixels are invisible to the human eye.
Ringing artifact #: Ringing artifacts are faint halos or ghost edges that appear around high-contrast boundaries in compressed images.

S

Safe zone #: The central area of social media content that stays visible without being covered by platform UI elements.
SMTP limit #: The maximum total size of a single email message including all attachments enforced by mail servers.
srcset attribute #: The srcset attribute enables responsive images by letting browsers choose optimal image sizes for each device automatically.
Structured data #: Machine-readable code that helps Google display your images in rich search results.
SVG #: XML-based vector format that scales infinitely without quality loss, perfect for logos and icons.

T

Thumbnail #: A small preview image that represents larger content and drives click-through decisions across digital platforms.
TIFF #: TIFF is a professional image format that preserves maximum quality for print and archival storage.
Transparency #: Image transparency allows pixels to be fully or partially see-through via an alpha channel.

U

Upscaling #: Increasing an image's pixel dimensions beyond its original size using interpolation or AI enhancement.

V

Viewport #: The viewport is the visible area of a browser window where webpage content displays.
Visual search engine #: A visual search engine lets users discover content by searching with images rather than text keywords.
Visually lossless #: Lossy compression that removes data while producing output indistinguishable from the original to human viewers.

W

Watermark #: A visible or invisible mark applied to images to identify ownership, assert copyright, and deter unauthorized use.
WebAssembly (Wasm)#: WebAssembly enables near-native speed image processing directly in your browser without server uploads.
WebP #: A Google-developed image format that creates smaller file sizes than JPEG and PNG.
Wide color gamut #: Wide color gamut refers to color spaces that display more colors than standard sRGB web images.
withoutEnlargement #: A resize constraint that prevents images from being made larger than their original dimensions.

X

XMP (Extensible Metadata Platform)#: XMP metadata stores your photo editing history and adjustments in Lightroom, Photoshop, and other image editors.

Ready to optimize your images?

Pictuary puts these concepts into practice — compress, resize, and crop images for free. No account required.

Compress an image Resize an image Resize for social media