Three formats, very different trade-offs. Here's what actually differs between them, and which one to pick before converting a whole folder of images at once.
Install ExtensionWhen you're resizing one image, picking a format is an afterthought. When you're batch-processing a whole folder — product photos, a photo shoot, a set of graphics — getting the format wrong means re-running the entire batch, or shipping files that are needlessly large or don't support the transparency you need. Bulk Image Resizer converts between JPG, PNG, and WebP in the same step as resizing, so it's worth knowing the real differences before you pick one for an entire batch.
| Format | Compression | Transparency | Typical use |
|---|---|---|---|
| JPG | Lossy — smaller files, some quality loss on re-compression | No | Photos: product shots, social posts, general web images |
| PNG | Lossless — larger files, no quality loss | Yes — full alpha channel | Logos, graphics with transparent backgrounds, screenshots, cut-out product images |
| WebP | Lossy or lossless, generally smaller than JPG or PNG at similar quality | Yes | Web images where smaller file size matters and the destination supports it |
You're converting ordinary photos — product shots, event photos, social media images — and you want broad, no-questions-asked compatibility. Every platform and marketplace accepts JPG without issue, which makes it the safest default for a mixed batch headed to multiple destinations.
Any image in the batch needs a transparent background — a logo, an icon set, or a cut-out product photo meant to sit on different colored backgrounds. PNG is also the right call for screenshots or graphics with sharp text and flat colors, where lossy compression would introduce visible artifacts.
You control the destination — your own website, a Shopify theme, an app — and want smaller file sizes without a visible quality hit. Before converting an entire batch to WebP, confirm the specific marketplace or platform you're uploading to actually accepts it; not every destination does.
If a folder already contains a mix of JPG, PNG, and other formats, you don't need to sort them first. Select the whole folder and choose one output format — the extension converts every file to that format in the same batch pass.
Re-saving a JPG repeatedly degrades it. Each time a JPG is opened, edited, and re-exported as JPG, a small amount of quality is lost from re-compression. If you're going to resize the same source images more than once (for different target sizes, say), it's worth keeping an uncompressed or PNG master and generating JPG outputs from that master each time, rather than resizing an already-compressed JPG.
File size adds up across a batch. PNG files are typically several times larger than a JPG or WebP at the same dimensions, because PNG compression is lossless. For a batch of a few images this barely matters; for a few hundred product photos destined for a storefront's media library, the difference in total storage and page-load weight is real.
Format and resizing happen in the same pass. There's no need to resize first and convert format in a separate tool afterward — picking your output format alongside your target dimensions and running the batch once covers both steps.
Before running format conversion across a large batch — a full product catalog, or hundreds of campaign images — it's worth converting a small handful first and checking the result: does the file size land where you expect, does transparency behave correctly if the image needs it, and does the destination platform display the format without issue? Confirming on a sample of five or ten images takes a minute and avoids re-running a multi-hundred-image batch because the wrong format was chosen for the whole set.
Need platform-specific pixel dimensions too? See the social media image size guide, or the seller batch-resize workflow. General questions are answered in the FAQ.