Every image you have ever opened is one of two fundamentally different things: a grid of coloured dots, or a set of drawing instructions. Almost everything else about image formats — why a photo belongs in JPEG but a logo belongs in SVG, why one file is 50 KB and a visually identical one is 5 MB, why a PNG keeps its transparent background and a JPEG fills it with white — follows from that single distinction and from how each format compresses its data.
This guide is the map. It explains the handful of concepts that make sense of all image formats, then links out to deeper articles on each. When you want to put the theory to use, the Universal Image Converter turns any of these formats into any other, entirely in your browser — nothing is uploaded.
Raster vs. vector: dots or instructions
A raster (or bitmap) image is a rectangular grid of pixels, each storing a colour. A 1920×1080 photo is just over two million pixels, each with a red, green and blue value. Because the grid has a fixed size, a raster image has a fixed resolution: enlarge it past its native size and the browser has to invent pixels, which is why photos go soft and blocky when blown up. PNG, JPEG, GIF, WebP, AVIF, BMP, TIFF and HEIC are all raster.
A vector image stores shapes instead — “a circle here, a curve there, filled with this colour.” The computer redraws those shapes at whatever size you ask for, so a vector logo is razor-sharp on a business card and on a billboard from the same tiny file. The trade-off: vectors describe geometry, not photographs, so you cannot save a sunset as a vector. SVG is the web vector format.
How compression shrinks an image
Storing every pixel literally is wasteful, so every modern format compresses. There are two philosophies, and knowing which one a format uses tells you almost everything about when to reach for it.
- Lossless compression packs the data so it can be perfectly reconstructed — not a single pixel changes. It works by spotting repetition (a row of identical sky-blue pixels becomes “blue × 400”). PNG, GIF, BMP, TIFF and QOI are lossless. Great for graphics; only modest savings on noisy photos.
- Lossy compression throws away detail the human eye barely registers — subtle colour shifts, high-frequency texture — to achieve dramatically smaller files. JPEG, WebP, AVIF and HEIC are lossy. A JPEG can be a tenth the size of the equivalent PNG and look identical on screen.
The catch with lossy formats is generation loss: every time you re-save, a little more detail is discarded, like photocopying a photocopy. We cover exactly what gets thrown away — and why JPEG can shrink a photo so far without you noticing — in Lossy vs Lossless Compression.
Colour depth and transparency
Two more properties decide what a format can represent. Colour depth (bit depth) is how many bits describe each pixel: 8 bits per channel gives the familiar 16.7 million colours, while 16-bit and HDR formats store far more for editing and high-dynamic-range work. Transparency needs an extra alpha channel that records how see-through each pixel is.
This is why a logo with a transparent background must be a PNG, WebP, AVIF or SVG and breaks as a JPEG — JPEG has no alpha channel at all, so it flattens transparency onto a solid colour (usually white). The full story of channels, bit depth, indexed palettes and alpha is in Colour Depth, Channels & Alpha.
The major formats at a glance
| Format | Type | Compression | Alpha | Best for |
|---|---|---|---|---|
| JPEG | Raster | Lossy | No | Photographs, complex imagery |
| PNG | Raster | Lossless | Yes | Screenshots, graphics, sharp edges, transparency |
| GIF | Raster | Lossless (256 colours) | 1-bit | Simple animation, tiny palettes |
| WebP | Raster | Lossy & lossless | Yes | Modern web — photos and graphics alike |
| AVIF | Raster | Lossy & lossless | Yes | Best-in-class web compression, HDR |
| HEIC | Raster | Lossy | Yes | iPhone photos (smaller than JPEG) |
| SVG | Vector | Text (gzip) | Yes | Logos, icons, diagrams, type |
| TIFF | Raster | Lossless (usually) | Yes | Print, archiving, scanning, editing masters |
For the three modern web formats that cause the most confusion, the head-to-head — file size, browser support, animation and transparency — is in PNG vs JPEG vs WebP vs AVIF, and the specific question of iPhone photos is covered in HEIC vs JPG.
Choosing a format in three questions
- Is it a photo or a graphic? Photo → a lossy format (JPEG, WebP, AVIF). Graphic, screenshot, or anything with sharp edges and flat colour → a lossless format (PNG), or SVG if it was drawn.
- Does it need transparency? Yes → PNG, WebP, AVIF or SVG. Never JPEG.
- Where will it be used? Modern website → WebP or AVIF for the smallest files. Maximum compatibility / email / old software → JPEG or PNG. Print or editing master → TIFF or 16-bit PNG. Logo or icon → SVG.
Converting between formats
Once you know what you have and what you need, conversion is the easy part. The Universal Image Converter reads 80+ input formats — every common one plus camera RAW, Photoshop PSD, GIMP XCF, HDR, and more — and writes to 140+ outputs, including fine-grained control over bit depth, quality and colour model. It detects your file by its magic bytes (not just the extension), handles alpha flattening for you when a target format has no transparency, and does the whole thing locally in your browser so your images are never uploaded.
With the concepts on this page you will know which output to choose; the converter handles the how. Read on into the linked deep-dives whenever you want to understand exactly what is happening to your pixels along the way.
Frequently asked questions
What is the difference between a raster and a vector image?
A raster image is a grid of coloured pixels at a fixed resolution — photos are raster. A vector image is a set of mathematical shapes (lines, curves, fills) that can be drawn at any size without blurring — logos and icons are usually vector. Raster scales down well but blurs when enlarged; vector scales infinitely but cannot represent a photograph.
Which image format is best?
There is no single best format — it depends on the content. Use JPEG or AVIF/WebP for photographs, PNG for screenshots and graphics with sharp edges or transparency, SVG for logos and icons, and a format like TIFF or PNG-48 when you need to preserve every bit for archiving or editing.
Does converting between formats lose quality?
Converting from a lossy format (like JPEG) re-compresses the already-degraded pixels, so quality can drop a little each time. Converting to or from a lossless format (PNG, TIFF, BMP) does not lose data. Converting a lossy source to a lossless target stops further loss but cannot recover detail the original JPEG already threw away.
Why does my PNG look the same as my JPEG but is ten times larger?
PNG stores every pixel exactly (lossless), while JPEG discards fine detail the eye barely notices (lossy) to shrink the file dramatically. On a photograph the two can look identical on screen while the JPEG is a fraction of the size — which is why photos belong in JPEG/WebP/AVIF and PNG is reserved for graphics and transparency.