Image Format Converter
Convert between JPG, PNG, WebP, and BMP — entirely in your browser. Nothing is uploaded.
Why Image Format Still Matters in 2024 (And What Nobody Tells You)
Pick up any stock photo library, screenshot tool, or design export and you will end up with files in half a dozen formats — often the wrong one for the job. A PNG screenshot of a chat conversation sits at 3.2 MB when a JPG at quality 85 would be 180 KB. A JPG product photo with a crisp white background becomes a blurry smear when someone expects transparency. The format you choose is not a cosmetic detail; it is a decision that affects page speed, storage costs, print quality, and whether a transparent element renders correctly or shows up with an ugly white box.
The four formats you encounter most often — JPG, PNG, WebP, and BMP — each exist because a different set of engineers faced a different set of problems and made deliberate trade-offs. Understanding those trade-offs is what separates someone who just converts files from someone who chooses the right format to begin with.
JPG: The Compression Workhorse With a Hidden Cost
JPEG was designed in the late 1980s by the Joint Photographic Experts Group specifically for photographs, and the fundamental mechanism — the Discrete Cosine Transform — is still doing the work today. The encoder divides an image into 8×8 pixel blocks and discards frequency information the human visual system struggles to detect. At quality 85, most people cannot distinguish a compressed photograph from the original. At quality 60, you start seeing blocking artifacts around high-contrast edges. Below 50, photos begin to look like they were printed on wet paper.
The catch is permanence. Every time you save a JPG, the compression runs again on data that has already been compressed. Save the same photograph ten times and you will eventually see visible degradation even at high quality settings — a process called generation loss. For a working file that gets edited repeatedly, JPG is the wrong choice. For a final export of a photograph that will not be edited again, it is nearly always the right one.
One other constraint worth knowing: JPG has no alpha channel. There is no such thing as a transparent JPG. If your image has transparency and you convert it to JPG, the converter has to make a decision about what color to put in the transparent areas. Most tools use white, which is correct for most use cases, but not all.
PNG: Lossless and Honest
Portable Network Graphics replaced GIF in the late 1990s and brought two things GIF could not offer: a full 24-bit color space and — critically — an 8-bit alpha channel for smooth transparency gradients. PNG uses DEFLATE compression, which is completely lossless. The pixel data you put in is exactly what you get out, every time.
The trade-off is file size. A PNG of a photograph will typically be two to five times larger than a JPG at quality 85. For photographs, this is usually not justified. Where PNG earns its keep is logos, UI screenshots, icons, and any image where you need hard edges, exact colors, or transparency. A company logo exported as JPG will have compression artifacts around the letterforms. The same logo as PNG will be clean regardless of how many times it is loaded or re-used.
PNG also has a "PNG-8" mode (indexed color, up to 256 colors) which can be surprisingly compact for simple graphics, though most modern tools export PNG-24 by default.
WebP: The Pragmatic Modern Choice
Google released WebP in 2010 and it took about a decade to get real browser support. Now that it is supported everywhere that matters, the question is whether to use it. The answer for web delivery is almost always yes.
WebP supports both lossy and lossless compression, and it supports transparency — making it a single format that can replace both JPG and PNG in most web contexts. The compression efficiency is genuinely better: a WebP at equivalent perceptual quality is typically 25–35% smaller than a JPG, and lossless WebP is often 20–30% smaller than PNG. For a site delivering hundreds of images, this translates directly to lower bandwidth costs and faster load times.
The one context where WebP falls short is print. If someone is preparing an image for a print workflow, PDF, or design software that does not speak WebP, they will need JPG or PNG. But for anything destined for a web browser, WebP is the format you probably should have been using for the last five years.
BMP: The Uncompressed Baseline
Bitmap is the oldest of the four, a Microsoft format from 1988 that stores pixel data with essentially no compression. A 1920×1080 BMP in 24-bit color will be approximately 5.9 MB every time, regardless of content. There is no quality setting because there is no quality loss — you get exactly the raw pixel values.
BMP's use cases are narrow but real. Certain industrial software, embedded systems, and legacy Windows applications expect BMP and nothing else. Windows wallpapers historically used BMP. Some image processing pipelines use it as an intermediate format specifically because there is no decode step — you can map the file to memory and read pixel values directly. For anything else, BMP is a format you convert from, not to.
How Canvas-Based Conversion Actually Works
When you convert an image in a browser using the Canvas API, the sequence is: decode the source image into raw RGBA pixel data, paint those pixels onto a canvas element, then call toDataURL() or toBlob() with the target MIME type and quality setting. The browser's own image codecs handle the actual encoding, which means the output quality matches what the platform's native encoder produces.
One nuance that trips people up: when converting to JPG, any transparent pixels in the source image need to be composited against a background before encoding, because JPG cannot represent alpha. A proper converter fills the canvas with white (or the desired background color) before drawing the source image. If you skip this step, the transparent areas will usually render as black in the output — the default canvas background before any drawing.
The quality parameter, a number between 0 and 1, maps directly to the encoder's quality setting. For JPG this is the JPEG quality factor; for WebP it controls a similar perceptual quality target. For PNG and BMP, the parameter is ignored — these formats produce identical output regardless of what quality value you pass.
Choosing the Right Format for Your Situation
The decision tree is shorter than most guides suggest. Photograph destined for a website? WebP, quality 80–90. Photograph destined for print or a workflow you do not control? JPG, quality 90–95. Image with transparency for web use? WebP or PNG. Logo or screenshot where pixel-perfect accuracy matters and file size is secondary? PNG. Legacy software or embedded system that only accepts uncompressed pixel data? BMP. Anything else? Start with WebP and only switch if something breaks.
The dimension that most guides skip is the re-editing question. If an image will be opened, modified, and saved again — a working Photoshop file, a document image — always keep it in a lossless format (PNG, BMP, or the application's native format) until you produce the final export. Only convert to a lossy format like JPG or lossy WebP at the last step before delivery, and never re-save the lossy file again.
Getting format selection right is a small decision that compounds across thousands of images in a production environment. A team that ships WebP instead of JPG across a hundred-page website reduces image payload by roughly a third with zero visible quality difference. A developer who reaches for PNG for every image on a photo-heavy site may be shipping five times more data than necessary. The format is not a file extension — it is a compression strategy, and each one was built for a specific job.