Why Does Piping Raw Image Bytes Through a PowerShell Function Fail?

The direct form works because chafa itself understands `-` and has the native-program logic needed to read standard input. Your wrapper currently just launches `chafa.exe --size=70x -f sixel` and ignores anything arriving at the function. For this raw-byte case, the simplest solution is to keep the native commands directly connected rather than putting a PowerShell function between them.

The function also doesn't receive or forward pipeline input. `img -` doesn't automatically mean “read stdin” here; the dash is just an argument, and PowerShell functions don't interpret it like a native program does. You would need a pipeline-bound parameter and code that explicitly writes the received data to the child process's standard input using .NET APIs such as `System.Diagnostics.Process`.

PowerShell can pass native stdout as raw bytes when one native executable is directly piped to another. In the second command, the pipeline target is a PowerShell function, so PowerShell handles the data through its object pipeline instead of connecting the native programs' standard streams directly. The bytes are no longer preserved as a raw stdin stream for chafa.