tinyfits

A single-header, zero-dependency FITS image reader/writer for C/C++.

Tinyfits supports a subset of FITS features that are commonly used in amateur astrophotography. It is designed to be easy to use, small, and reasonably fast.

Supports

• Grayscale, RGB, and multi-plane images
• 8/16/32-bit integer and 32/64-bit floating point format images
• Keyword reading, modification, addition, and deletion
• FITS image writing
• Pixel data conversion to float32 via tinyfits_to_float()
• Custom memory allocation

Not supported

• Multi-HDU / extension files (only the primary image is read)
• 64-bit integer data
• FITS images with BSCALE != 1
• FITS images with BZERO other than standard values that indicate unsigned data
• Compressed images (Rice, GZIP, HCOMPRESS)
• Binary or ASCII tables
• Automatic concatenation of CONTINUE long strings
• HIERARCH keywords

Usage

Copy tinyfits.h into your project. In exactly one .c or .cpp file:

#define TINYFITS_IMPLEMENTATION
#include "tinyfits.h"

All other files #include "tinyfits.h" for the declarations.

Load an image

TinyFits info = {0};
void* pixels;
int err = tinyfits_load(&info, "light.fits", &pixels);
if (err != TINYFITS_OK) { /* handle error */ }

// info.width, info.height, info.num_channels, info.pixel_type
if (info.pixel_type == TINYFITS_UINT16) {
    uint16_t* px = (uint16_t*)pixels;
    // ...
}

tinyfits_free_buffer(pixels);
tinyfits_free(&info);

Read keywords without loading pixels

TinyFits info = {0};
tinyfits_info(&info, "light.fits");
const char* bayer = tinyfits_get_keyword(&info, "BAYERPAT");
tinyfits_free(&info);

Write an image

TinyFits info = {0};
info.width = 1024;
info.height = 768;
info.num_channels = 1;
info.pixel_type = TINYFITS_UINT16;
tinyfits_set_keyword(&info, "INSTRUME", "ZWO ASI2600MC Pro", "");
tinyfits_save(&info, pixels, "output.fits", 0);
tinyfits_free(&info);

API

Function	Description
tinyfits_load	Load image from file (returns native-format pixels)
tinyfits_load_from_memory	Load image from memory buffer
tinyfits_info	Read keywords/dimensions from file (no pixels)
tinyfits_info_from_memory	Read keywords/dimensions from memory (no pixels)
tinyfits_save	Write image to file
tinyfits_save_to_memory	Write image to memory buffer
tinyfits_to_float	Convert native pixels to float32
tinyfits_free	Free metadata (keywords)
tinyfits_free_buffer	Free library-allocated pixel/data buffers
tinyfits_get_keyword	Look up a keyword value by key
tinyfits_get_keywords	Get all values for a repeating keyword (HISTORY, etc.)
tinyfits_set_keyword	Set or replace a keyword
tinyfits_add_keyword	Append a keyword (for HISTORY, COMMENT)
tinyfits_remove_keyword	Remove a keyword
tinyfits_image_size	Pixel buffer size in bytes
tinyfits_error_string	Convert error code to string

Building the tests

# Compile and run (MSVC)
cl /W4 /D_CRT_SECURE_NO_WARNINGS test_tinyfits.c /Fe:test_tinyfits.exe
test_tinyfits.exe

# Compile and run (GCC/Clang)
cc -Wall -Wextra -O2 test_tinyfits.c -o test_tinyfits -lm
./test_tinyfits

License

Public domain or MIT, depending on your needs. See LICENSE or the end of tinyfits.h for details.