The result of going down a very deep rabbit hole. I learned a lot about analog signal processing, television, and the NTSC standard in the process. Written to be compatible with C89.

Just like King's Crook (my from-scratch 3D game), this code follows the same restrictions:

1. Everything must be done in software, no explicit usage of hardware acceleration.
2. No floating point types or literals, everything must be integer only.
3. No 3rd party libraries, only C standard library and OS libraries for window, input, etc.
4. No languages used besides C.
5. No compiler specific features and no SIMD.
6. Single threaded.

This program performs relatively well and can be easily used in real-time applications to emulate NTSC output.

================================================================ Feature List:

• Somewhat realistic/accurate composite NTSC image output
  -- with bandlimited luma/chroma
  -- color artifacts (extends to being able to show specially patterned b/w images as color)
• VSYNC and HSYNC
• Signal noise (optional)
• Interlaced and progressive scan
• Monochrome and full color
• Vertically aligned chroma OR checkerboard chroma (specified in #define in header)

The command line program provided does not let you mess with all the settings like black/white point, brightness, saturation, and contrast.

In the ntsc_crt.c file, there are two main()'s. One is for a command line program and the other uses my FW library (found here https://github.com/LMP88959/PL3D-KC) to provide real-time NTSC emulation with adjustable parameters.

The famous waterfall 'rainbow' effect created as a result of dithering will show if it is compiled with CRT_DO_CHK_C set to 0. Specially patterned black and white images can be encoded/decoded with color just like a real composite NTSC display.

cd NTSC-CRT

cc -O3 -o ntsc *.c

or using CMake on Linux, macOS, or Windows:

cmake -B build
cmake --build build
build/ntsc

The default command line takes a single PPM image file and outputs a processed PPM file:

usage: ./ntsc -m|o|f|p|r|h outwidth outheight noise phase_offset infile outfile
sample usage: ./ntsc -op 640 480 24 3 in.ppm out.ppm
sample usage: ./ntsc - 832 624 0 2 in.ppm out.ppm
-- NOTE: the - after the program name is required
	phase_offset is [0, 1, 2, or 3] +1 means a color phase change of 90 degrees
------------------------------------------------------------
	m : monochrome
	o : do not prompt when overwriting files
	f : odd field (only meaningful in progressive mode)
	p : progressive scan (rather than interlaced)
	r : raw image (needed for images that use artifact colors)
	h : print help

by default, the image will be full color, interlaced, and scaled to the output dimensions

There is also the option of "live" rendering to a video window from an input PPM image file:

cmake -B build -Dlive=on
cmake --build build
build/ntsc my.ppm

If you have any questions feel free to leave a comment on YouTube OR join the King's Crook Discord server :)

YouTube: https://www.youtube.com/@EMMIR_KC/videos

Discord: https://discord.gg/hdYctSmyQJ

itch.io: https://kingscrook.itch.io/kings-crook

Feel free to use the code in any way you would like, however, if you release anything with it, a comment in your code/README saying where you got this code would be a nice gesture but it’s not mandatory.

Thank you for your interest!