Images · PRACTICAL GUIDE
Image pixels, file size and formats explained
Understand dimensions, compression, transparency and format choices before preparing an image.
Dimensions and file size measure different things
A 400 × 300 image contains 120,000 pixels. Its compressed byte size depends on the format, visual complexity, metadata and encoder settings. A plain-color logo and a detailed photograph at identical dimensions can therefore have very different file sizes.
Use Image inspector to read actual file bytes and oriented dimensions rather than estimating one from the other. The built-in sample is a generated colored graphic; its exact encoded size varies by browser.
Choose a format for the content
JPEG supports lossy compression and has no alpha channel. PNG can retain transparent pixels and sharp raster detail, but quality sliders do not work like JPEG quality. WebP can support transparency and different compression characteristics, subject to the browser’s encoder support.
Changing the extension alone changes none of these properties. A real conversion decodes and re-encodes the pixels.
Transparency must land somewhere
When a transparent logo becomes JPEG, its transparent regions need an opaque background. Choose the actual page or document background—white is common, but not universal. Preview edges as well as large transparent regions because partially transparent pixels are blended with the matte.
Re-encoding a JPEG as PNG cannot recover discarded detail. Output metadata should not be assumed to match the original file, nor should a new raster export be treated as a certified metadata scrub.
A repeatable inspection workflow
Record original dimensions and bytes. Convert the original separately to each supported format and inspect each output rather than chaining repeated conversions. Reopen the downloaded files in their target application to check transparency and compatibility.
This release accepts static JPEG, PNG and WebP under 10 MiB and 16 megapixels. It deliberately rejects animations, SVG and HEIC rather than pretending to preserve unsupported features.
Put it into practice
Choose the tool that matches your next step. Keep an original copy and inspect the result before using it elsewhere.
Image size and dimension checkerUnderstand why an image fails requirements.ImagesImage resizerMeet a pixel-dimension requirement.ImagesImage format converterUse a supported format in another app.Images