Image Format Detector
Detect the true format of any image by reading its magic bytes. See format, MIME type, dimensions, transparency, and color depth. Free and private.
Drop your image here
or click to browse files
Image Format Detector Features
Accurate format detection from binary file headers, not just file extensions.
Reads the binary header of your file to identify the true format regardless of what the file extension says.
Loads the image to report exact pixel dimensions, transparency support, and color depth information.
Only the first 32 bytes are read for format detection. The full file is processed locally with no server upload.
What Is Image Format Detection?
Every image file format has a unique signature in its first few bytes, called magic bytes or a file header. This tool reads that signature to determine the true format of your file, independent of the filename or extension. It also loads the image to measure dimensions and detect transparency.
Frequently Asked Questions
Why does true format detection matter?
File extensions can be misleading. A file named image.jpg might actually contain WebP or PNG data if it was renamed.
Applications that rely on extensions may fail to open or process such files correctly.
Reading the binary header gives a definitive answer about the actual format.
What are magic bytes exactly?
Magic bytes are a fixed sequence of bytes at the beginning of a file that serve as a format identifier.
For example, JPEG files always start with FF D8 FF. PNG files start with 89 50 4E 47 0D 0A 1A 0A.
Operating systems and applications use these signatures to identify file types reliably.
How is PNG transparency detected specifically?
PNG files contain an IHDR chunk starting at byte 8 of the file. Byte 25 of the file holds the color type value.
Color type 4 means grayscale with alpha channel. Color type 6 means RGBA, full color with alpha.
Only those two types support per-pixel transparency. Types 0, 2, and 3 do not have an alpha channel.
Can I detect HEIC format on Windows where it cannot be previewed?
Yes. The magic byte detection reads only the binary header and does not require the browser to decode the image.
The format badge will show HEIC or HEIF based on the ftyp box brand in the file header.
Dimensions may show as unavailable if the browser cannot decode the HEIC image, but the format is still identified correctly.
What is the ftyp box in HEIC and AVIF files?
HEIC, HEIF, and AVIF all use the ISO Base Media File Format container. The first box in the file is the ftyp box.
The ftyp box contains a four-character brand code such as heic, mif1, or avif that identifies the specific format variant.
This tool reads bytes 8-11 of the file to extract this brand code for accurate identification.
Is color depth information accurate for all formats?
For PNG, color depth is read precisely from the IHDR chunk which contains bit depth and color type fields.
For JPEG, 24-bit is reported as standard since JPEG virtually always uses 8 bits per channel without alpha.
For WebP, HEIC, TIFF, and AVIF, the reported value is a typical range because the exact depth requires full file parsing.
What if the format shows as Unknown?
If the magic bytes do not match any known signature, the format is listed as Unknown.
This can happen with rare formats, corrupted files, or files that are not images at all.
The file name, size, and any dimensions the browser can load are still shown.
Does this tool work on mobile devices?
Yes. The FileReader API and Image API are available in all modern mobile browsers.
The interface is fully responsive and works on phones and tablets.
You can analyze images from your camera roll or file storage directly.