I work on OnePassApps. We build browser studios that work on files in the tab instead of uploading them. This one is the Image Studio's Convert tab - the step that turns one image format into another.

Most online image converters start by asking you to upload the file. That is the part that should make you stop if the picture is a passport scan, a medical record, or a client deliverable you were not planning to hand to a stranger. The OnePassApps Image Studio does the conversion in your own browser tab.

There is one catch worth knowing before you start, and it is not in the button label: JPEG cannot hold transparency. Below I show you exactly what that does to your pixels, and which output format keeps them.

What the tab says

The page line is plain: "Convert, compress, resize, crop and clean images in your browser. Nothing leaves this tab." The stage under the file repeats it: "Processing stays in this browser."

Convert is the first of the seven Image Studio tabs: Convert, Compress, Resize, Crop, Remove background, Remove metadata, and Images to PDF.

01 Source

No image yet. Drop one on the stage or browse for it.

The picker takes JPEG, PNG or WebP - up to 25 MiB and 25 megapixels. The file input itself accepts image/jpeg, image/png and image/webp, and it takes more than one file at a time.

02 Output

Three output formats - PNG, JPEG and WebP - a quality slider, and one line of advice:

JPEG has no transparency, so transparent areas become white.

03 Result

The new copy's size and format appear here.

The action button reads Convert image, and the original is never touched: the panel finishes with "Add an image to start. Your original stays untouched."

Run 1: a photographic PNG to JPEG

I built a 640 x 480 PNG with a gradient and grain (713.8 KiB) and converted it.

  • Before: 713.8 KiB PNG
  • After: 18.2 KiB JPEG
  • Dimensions: 640 x 480
  • File name: probe-convert.jpg
  • "Converted in 0.2 s"
  • Result card: JPEG - 640 x 480 - 18.2 KiB - 97% smaller

A percentage like that is an unfair headline for a synthetic gradient file, so do not treat it as a promise. What is checkable is the file itself: the downloaded bytes begin ff d8 ff e0 with a JFIF marker, and the size on disk matches the number the panel prints.

The result panel keeps both copies side by side, with buttons for the original and for the new file, plus a "Convert again" control, and it ends with:

Finished. Download a new copy; the original stays unchanged.

Run 2: the transparency question, answered with pixels

This is the part worth reading. I built a 200 x 200 PNG where the right half is fully transparent - 20,000 of the 40,000 pixels have zero alpha. I confirmed that in the tab before converting: the transparent corner read 0,0,0,0 and the opaque corner read 6,6,14,255.

Converted to JPEG, the panel read:

  • Before: 54.7 KiB PNG
  • After: 3.6 KiB JPEG
  • Dimensions: 200 x 200
  • File name: probe-alpha.jpg
  • "Converted in 0.3 s"

Then I read the output's pixels instead of trusting its summary line. The JPEG has zero transparent pixels, and the corner that had been transparent came back as white - 255,255,255. The transparency was not compressed away; it was flattened onto a white background, exactly as the panel warned.

The same source file, converted to WebP instead:

  • After: 2.5 KiB WebP
  • File name: probe-alpha.webp
  • "Converted in 0.4 s"
  • Result card: WebP - 200 x 200 - 2.5 KiB - 95% smaller

Its bytes are a real RIFF/WEBP file, and it still holds 20,000 transparent pixels - the same count as the input. Nothing was flattened.

So the rule comes out of the measurement rather than the marketing:

  • Transparent PNG to JPEG: the transparent areas turn white.
  • Transparent PNG to WebP or PNG: the alpha channel survives.

If your image is a logo, a cut-out screenshot, or any design on a transparent background, keep PNG or WebP. If it is a photograph, JPEG is the smaller file and the flattening question does not arise.

The quality slider runs from 10 to 100 and starts at 86. I left it at the default for both runs above, so I am not going to guess what another setting does to the numbers - that is the panel's job, and it shows you the before and after sizes either way.

What it costs

The browser studios run on the OnePassApps membership. Standard is free right now at $0/month, with 100,000 credits every 30 days, no end date set and no card required, and no automatic paid subscription. You do not need an account to use the studios.

Try it on your own image: the Image Studio.

Every studio has a plain-language guide with the limits and the tool list: the OnePassApps guides.

I work on OnePassApps, so of course I am biased about these studios. What I tried to keep true here is the small set of facts you can check yourself: the accepted formats and the size limit, the quality slider's range and default, the JPEG warning the panel prints, the two measured runs with their exact sizes, the raw bytes of both outputs, and the pixel counts that show precisely where the transparency went.