Bulk Image Converter

Transparency, and what JPG does to it

PNG and WebP can store an alpha channel — the record of which pixels are see-through. JPG cannot. There is no way to save a transparent JPG, so converting one means deciding what colour goes behind the image.

The usual failure is that nothing decides, and the transparent areas come out black — because an empty canvas is transparent black and JPG keeps the colour while dropping the transparency. This tool always fills first, with white by default, and tells you which of your images are affected before you convert. If you need the transparency kept, convert to PNG, WebP or ICO instead.

Choosing between JPG, PNG, WebP and ICO

• WebP — usually the best choice for the web. Typically 25–35% smaller than a JPG at the same visual quality, supports transparency, and is supported by every current browser.
• PNG — lossless, with transparency. The right answer for logos, screenshots and anything with sharp edges that has to stay pixel-exact. Photographs saved as PNG are usually much larger than they need to be.
• JPG — photographs, and anywhere that has to open a file without question. No transparency, and every save loses a little quality.
• ICO — favicons and app icons, not photographs. Each file holds the image at 16, 32, 48 and 256 pixels, fitted onto a transparent square without being stretched. It is still made of pixels, not a vector, so it does not stay sharp at sizes it was not made for.

Reading SVG, TIFF and HEIC

SVG files are drawn by your browser as images and turned into pixels at the size the file declares — its width and height, or its viewBox when those are missing — and are never scaled up, so a 24×24 icon comes out 24×24. A file with no size at all is drawn at 300×150. SVGs over 16,384 pixels on a side or 40 megapixels in all are refused, as are files containing scripts, links to external images, fonts or stylesheets, embedded HTML or animation. Nothing is ever saved back as SVG.

TIFF is read for its first page only. Uncompressed, LZW and Deflate files in greyscale, palette or RGB, with or without transparency, are supported; BigTIFF, other compressions such as JPEG, PackBits and CCITT, CMYK and other colour models, floating-point samples and TIFFs marked to be rotated or mirrored are refused, each with its reason. Pages over 16,384 pixels on a side or 25 megapixels are refused too. Your browser cannot open TIFF itself, so it is decoded in the background, and a large file can take a few seconds.

HEIC and HEIF — the format iPhones save photos in — are decoded in your browser by libheif, compiled to WebAssembly and running in the background. The main photo is converted, the right way up, at up to 50 megapixels; depth maps, burst frames and the video half of a Live Photo are not. For a folder of phone photos, the HEIC to JPG converter opens with JPG already chosen. There are ready-made pages for WebP to JPG, AVIF to JPG, PNG to JPG, JPG to PNG, JPG to WebP and PNG to WebP too.

Why convert in the browser?

Re-encoding an image is arithmetic on pixels your computer already has. Sending a file to a server to have that done, then sending it back, is slower for a large batch, costs someone money per image, and puts your files on a machine you do not control. Doing it locally is the reason this tool has no sign-up and no usage limit.

Frequently asked questions

Are my images uploaded anywhere?

No. Every step happens in your browser. JPG, PNG, WebP, BMP, GIF and AVIF are decoded by the browser itself; an SVG is checked by the page and then drawn by the browser as an image; a TIFF is decoded by a JavaScript decoder running in a background worker in the same tab; a HEIC or HEIF is decoded by libheif, compiled to WebAssembly, in a background worker too. The result is written with the browser’s canvas — an AVIF by an encoder compiled to WebAssembly in a background worker in the same tab — and an ICO is assembled from the PNGs the canvas produces. Your images are never sent to a server, which is why the tool needs no account and has no usage limit.

What happens to transparency when I convert to JPG?

JPG has no transparency. Converting a transparent image to JPG replaces the transparent areas with a solid colour, which is white by default and which you can change before converting. The tool marks which of your images are transparent so nothing is a surprise. Convert to PNG or WebP instead if you need the transparency kept.

Which formats can I convert between?

JPG, PNG, WebP and AVIF convert in any direction, and any image the tool reads can also be saved as an ICO icon. BMP, GIF, SVG, TIFF, HEIC and HEIF can be read but not written back — the browser canvas writes JPG, PNG and WebP, AVIF is written by an encoder compiled to WebAssembly, and an ICO is built from PNGs — so a BMP, a TIFF or an iPhone HEIC photo comes out as JPG, PNG, WebP, AVIF or ICO, and an SVG is turned into pixels. For HEIC and HEIF only the main photo is converted, not depth maps or burst frames. TIFF is read for its first page only, and only uncompressed, LZW or Deflate files in greyscale, palette or RGB, with or without transparency; BigTIFF, other compressions such as JPEG, PackBits or CCITT, CMYK and other colour models, and TIFFs marked to be rotated or mirrored are refused with the reason. SVGs containing scripts, external files, embedded HTML or animation are refused too. Animated GIFs, animated WebPs and APNGs are refused rather than accepted, because a canvas only ever sees the first frame and the animation would be silently lost.

Why is there no quality setting for PNG?

PNG is a lossless format — the browser encoder ignores a quality setting entirely, so showing one would be a control that does nothing. Quality applies to JPG and WebP.

Which format should I choose?

WebP is usually the best choice for the web: it is typically 25 to 35 per cent smaller than a JPG at the same visual quality and it supports transparency. Use PNG when you need lossless quality or sharp edges, and JPG when the file has to open anywhere at all.

Related reading

Working out a batch workflow? There is a guide to batch image processing, and if you are selling online, see Amazon’s photo requirements.