Module ImageStreamIO {#page_module_ImageStreamIO}
Image stream definitions and tools.
Overview
ImageStreamIO implements a shared memory image format, refered to as stream, for low-latency high throughput I/O.
This is generally used for images, for example dumping the ouptut of a high speed camera onto shared memory, but can also be used for any data requiring fast I/O. The format includes semaphores for low-latency IPC.
How to read/write to/from streams
The interface protocol can be either:
- Slow interface by reading and writing FITS files. Command-line scripts are provided to apply FITS file to DM and also to read FITS files from any camera
- Fast interface by direct access to shared memory. This option is done by loading shared library and calling it from C program. A Python version also exists; which is slightly slower.
Approximate speed / timing accuracy:
- Option #1 is very slow (few 100 Hz max) and timing stability is probably no better than 50ms
- Option #2 from Python supports ~kHz and timing stability is probably at ms level (I haven't measured it ... just guessing)
- Option #2 from C program supports >10 kHz (- so it is limited by camera speed, not software) and timing stability is ~10us
For options (1) and (2) with C, you can install milk package: https://github.com/milk-org/milk
Command line interface (slow) details
Download and install the milk package.
The scripts to interface FITS files with our data streams are in: https://github.com/milk-org/milk/tree/master/scripts
Look for scripts :
- shmim2fits : Converts stream to FITS file
- Fits2shm : Writes FITS file to stream
C interface (fast) details
Link ImageStreamIO to your program and call IO functions directly.
See example source code in ImageStremIO module: ImCreate_test.c.