Resizing is three numbers, and only one of them is yours to set
Most resize tools give you a slider or a handful of presets. That is fine until you need an exact pixel size for a form, a sprite sheet or a CMS that rejects anything else - at which point you end up guessing and checking the result by hand.
The Image Studio's Resize tab in OnePassApps takes the opposite approach: it shows you the width, the height and the scale of your image as live numbers, tells you which of them are locked, and hands you the resized file so you can check it yourself.
Full disclosure: I work on OnePassApps. This is the Resize tab in the Image Studio, checked in the live tab while writing this - every number below came out of a run I made, not out of the marketing copy.
Open it here: the Image Studio
The panel
The Image Studio carries seven tool tabs on one page: Convert, Compress, Resize, Crop, Remove background, Remove metadata, Images to PDF. The page line above them reads "Convert, compress, resize, crop and clean images in your browser. Nothing leaves this tab."
The Resize tab is laid out as three numbered steps.
01 Source - "Add an image to start. Your original stays untouched." The picker accepts JPEG, PNG or WebP · up to 25 MiB and 25 megapixels, and the page repeats "Processing stays in this browser."
02 Dimensions - "Width, height and scale appear here once an image is open. They start at its real size." Three number fields - Width (px), Height (px) and Scale (%) - then two checkboxes, Lock aspect and Prevent upscaling, a Format row of PNG, JPEG and WebP, a Quality control, and the line "Resampled in this browser, up to 25 megapixels."
03 Result - "The new copy's size and format appear here."
The action button is Resize image, and after a run it becomes "Resize again". The panel also carries a "Fit" / "100%" preview zoom and a Result / Original toggle so you can compare the two side by side.
Three numbers, and which one you actually touch
Open a 400 × 300 image and the fields read 400, 300 and 100. Type 100 into the width and the height does not stay at 300 - it becomes 75, and the scale drops to 25. That is the Lock aspect checkbox doing its job: it is on by default, and it keeps the ratio of your image while you resize it.
Set the scale instead and the other two follow. Scale 50 on the same 400 × 300 image gave 200 × 150 automatically.
So with the lock on, you type one number and the panel does the arithmetic. The fields are not three separate settings; they are three views of the same decision.
The limits are visible in the markup rather than buried: width and height run from 1 to 12000, the scale field from 1 to 400, and the quality control from 10 to 100, starting at 86.
The checkbox that stops you making the file worse
Prevent upscaling is also on by default, and it is the one that surprises people. With it on, typing a width larger than the source is refused: on the 400 × 300 image, entering 800 left the field reading 400, with the height back at 300 and the scale back at 100.
Turn it off and the same 800 is accepted. The width field became 800, the height followed to 600, and the scale showed 200.
That is a deliberate guard rather than a limit on the format. Enlarging a 400 × 300 image to 800 × 600 invents 240,000 pixels that were never in the file - they are filled in by interpolation, so you get a bigger file with less real detail in it. The checkbox is there so that "make it bigger" is something you ask for on purpose.
Proving the output instead of trusting the panel
Here is the run, in full, on a 400 × 300 PNG I generated myself (four flat colour quadrants with a black marker square in the top-left corner).
Run 1 - downscale to 100 px wide. Width 100, lock aspect on, default JPEG. The panel reported:
- "Before 1.8KiB PNG"
- "After 1.3KiB JPEG"
- "Dimensions 400 × 300 → 100 × 75"
- "File name probe-resize.jpg"
- "Resized in 0.2 s"
- "JPEG · 100 × 75 · 1.3 KiB · 24% smaller"
The exported file was a real JPEG - 1,378 bytes with a JFIF header. Reading its pixels back, the top-left pixel was black (0,0,0,255), the top-right green (0,255,0,255), the bottom-left blue (0,0,255,255) and the bottom-right white (255,255,255,255): the same four quadrants, resampled into the smaller frame, in the same places.
Run 2 - upscale to 800 px wide. Prevent upscaling off, width 800. The panel reported "Dimensions 400 × 300 → 800 × 600", "After 6.9KiB JPEG" and "JPEG · 800 × 600 · 6.9 KiB · 290% larger". The exported file was 7,064 bytes of JPEG, and the four corner pixels still read black, green, blue and white.
Run 3 - PNG output at 120 px wide. Format PNG, width 120, height followed to 90, scale 30. The panel reported "After 618B PNG", "Dimensions 400 × 300 → 120 × 90", "PNG · 120 × 90 · 618 B · 66% smaller". The exported file's IHDR header read 120 × 90, and its corner pixels read black, green, blue and white again.
The default output format is JPEG, and the size line can read "larger"
The Format row defaults to JPEG, so the first resize I made came out as "probe-resize.jpg" even though the source was a PNG.
Read the size line before you take it. Upscaling that flat-colour PNG to 800 × 600 produced "6.9 KiB · 290% larger" - the file got three and a half times the size of the original, because JPEG re-encodes what PNG had stored losslessly and the result is still only 400 × 300 of real pixels. The panel is not hiding it: it shows the before and after sizes, the percentage, and a Result / Original toggle so you can compare the two.
Pick PNG when you want a lossless result. The same downscale to 120 × 90 came out at 618 bytes, against 1.8 KiB for the source - 66% smaller, and every pixel in it still exactly matches the colour it came from.
What you get at the end
The result panel gives you the file name, the format, the pixel dimensions, the size change, the time it took ("Resized in 0.2 s"), and a Download button. The closing line is the honest one: "Finished. Download a new copy; the original stays unchanged." Your source file is never overwritten, and you keep both copies side by side.
Why do it in the tab at all
The usual reason to resize something is that it goes somewhere you do not control - an upload box that wants exactly 800 × 600, a form with a size limit, an avatar field that wants a square. Those are exactly the files you would rather not hand to a stranger's server, and this tab never sends them: the page says "Nothing leaves this tab." and "Processing stays in this browser.", and the only thing that leaves the browser is the file you download yourself.
Full disclosure again: I work on OnePassApps. The Image Studio is free right now during the promotional period - Standard is $0/month with 100,000 credits every 30 days, no end date set and no card required, and existing paid subscriptions keep their terms. If you want the other tabs in the same place, the guides are here: OnePassApps app guides
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