Editorial policy

Who writes and checks the content

Pages are written and maintained by Rundong Li, Pixohub’s founder, who also oversees how each tool is tested and how every specification is checked. More about him and why Pixohub exists is on the About page. We use software, including AI tools, to help draft and proofread text and to run our tests at scale. We don’t publish a figure we haven’t measured ourselves or found on the official source we cite, and we correct errors as soon as we learn about them.

How we test the tools

Our measurements come from the same code you use. We drive each tool page in a real browser (Chromium, plus Firefox and WebKit for compatibility checks) with a script that uploads a file, waits for the result and saves exactly what the download button would give you. We then measure the saved files.

The test images

• 20 photos from recent iPhones (12 to 48 megapixels), picked at random from Wikimedia Commons categories of photos taken with iPhone 12 to 15 and released under Creative Commons or public-domain terms. They cover city streets, interiors, night scenes, landscapes and close-ups. The full list with credits is below.
• The 24 images of the Kodak Lossless True Color Image Suite, 768 × 512 px, a standard set for image-compression research. They stand in for photos that are already web-sized.
• Format test files: one of the photos above resized to 1600 × 1200 with its camera metadata kept, and an original 800 × 600 graphic with a transparent background, gradients, a soft shadow and text, each saved in all 13 formats our converters accept.

What we measure

• File size in bytes, and whether a compress-to-size result is actually under the target.
• Visual similarity to the original with SSIM (structural similarity, 1.0 = identical), computed on luminance after scaling both images to 1080 px wide, roughly what a phone screen shows. This counts lost resolution and compression artefacts together. For format conversions we also check whether the pixels are bit-for-bit identical.
• Output dimensions, estimated JPEG quality, and processing time in the browser.
• Whether transparency and camera metadata (EXIF) survive.
• For the colour converters, every possible input value: all 16,777,216 HEX/RGB colours, all 3,672,360 whole-number HSL and HSV values and all 104,060,401 whole-number CMYK values.

Every results table shows the date of the test. We re-run the tests whenever the code that produces the output changes, and at least every six months. When a test exposes a bug we fix the tool first and publish the results of the fixed version. That happened in October 2026: the compress-to-size tool could miss small targets, AVIF output failed in Chrome and Firefox, WebP output failed in Safari, and PPM files were refused. All four are fixed.

How we verify passport and visa photo rules

• We use only the issuing government’s own pages: the ministry, passport office or immigration department, its official application portal, or an official embassy or consulate page. Each country page names its source and links to it where a stable link exists.
• Photo sizes, head-height ranges, background colours and file limits are copied from that source, not from photo-booth or visa-agency sites. Where official pages disagree (an English FAQ and a local-language FAQ, say), the page says so instead of picking one silently.
• We re-check every country at least every six months, and immediately when we learn of a change. Each page shows when its content last changed.
• Application steps are summarised from the same official pages. Fees change often, so we link to the fee page rather than quoting amounts.

How we verify platform image sizes

Sizes for social networks, marketplaces and apps come from each platform’s help centre, developer documentation or official ads guide. Third-party “size cheat sheets” are not used as sources. Where a platform publishes no size, the page says so and explains the reasoning behind our suggestion. We review platform specs every three months, because they change more often than government rules.

Corrections

If you spot a mistake or an outdated rule, please tell us through the contact page. Include the page and, if you can, a link to the official source. We aim to check and correct within a few days and update the page’s date when we do.

Advertising and independence

Pixohub is free and is supported by Google AdSense ads and an optional paid plan. Advertisers have no say over what we write, and no tool, platform or service pays to be mentioned.

Test image credits

The photos are used only to produce measurements; we don’t republish them. Thanks to their photographers.