What image formats are supported for upload?

Most modern QR readers accept PNG, JPEG, GIF, and WebP files. PNG is preferred because its lossless compression preserves the sharp black-and-white contrast that decoding algorithms rely on. JPEG compression can introduce artifacts around module boundaries, potentially causing read failures at lower error-correction levels. If a JPEG scan fails, converting the image to PNG before re-uploading usually resolves the issue.

Why does the reader fail on a QR code that looks perfect?

Visual clarity does not guarantee decodability. Common failure causes include insufficient quiet zone margin (the QR standard requires four module widths of white space on all sides), excessive image rotation beyond the decoder's tolerance, or a printed size so small that individual modules blur together. Additionally, QR codes with a custom logo overlay that exceeds the error-correction capacity of the chosen level will fail. Try increasing image resolution or switching to a higher error-correction level when regenerating the code.

Can the reader decode QR codes inside PDFs or screenshots?

Yes, as long as the PDF is rendered or the screenshot is cropped to show the QR code at sufficient resolution. The key requirement is that each module (the individual black or white squares) spans at least two to three pixels in the uploaded image. Heavily compressed PDFs may require rendering at a higher DPI before uploading. Screen-captured QR codes from monitors typically decode well because display pixel densities are high.

What is the difference between a QR code and a Micro QR code?

Standard QR codes (ISO/IEC 18004) range from Version 1 (21×21 modules) to Version 40 (177×177 modules) and support all four encoding modes. Micro QR codes are a compact variant defined in the same standard, ranging from M1 to M4, with the largest being only 17×17 modules. They encode less data and are suited for applications with very limited space, such as component marking in electronics manufacturing. Most general-purpose readers support both formats.

Is it safe to scan QR codes from unknown sources?

Scanning itself is safe; harm can only occur if you act on the decoded content. QR codes frequently encode URLs, and a malicious code may direct you to a phishing site or trigger an automatic download. Best practice is to preview the decoded URL before tapping it, verify the domain, and treat unfamiliar QR codes with the same caution as unsolicited links in email. Using a reader that displays the full URL before navigation provides an important safety layer.

เครื่องอ่าน QR Code

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