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This page lets you see what the binary data of any file looks like, by interpreting the raw byte values as pixel data.
The first button lets you load a file, the last one saves the generated image to your computer, and the ones in between change how the visualization is displayed. The color modes toggled by the second button are greyscale, RGB, and RGBA.
For best results, try files that are over a megabyte, as it takes about 8MB to fill a 1080p screen without using the zoom feature. Though, there is a 50MB limit for performance reasons.
Although this tool is entirely clientside, since it would be possible to convert a saved image back into the original data if it were shared with others, you shouldn't use this tool with any sensitive files.
I like to use EXE and DLL files as they usually have pretty interesting patterns, and sometimes you can see the embedded icons (RGBA mode is usually best for that).