63 lines
3.7 KiB
C
63 lines
3.7 KiB
C
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// //////////////////////////////////////////////////////////
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// toojpeg.h
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// written by Stephan Brumme, 2018-2019
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// see https://create.stephan-brumme.com/toojpeg/
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//
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// This is a compact baseline JPEG/JFIF writer, written in C++ (but looks like C for the most part).
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// Its interface has only one function: writeJpeg() - and that's it !
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//
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// basic example:
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// => create an image with any content you like, e.g. 1024x768, RGB = 3 bytes per pixel
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// auto pixels = new unsigned char[1024*768*3];
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// => you need to define a callback that receives the compressed data byte-by-byte from my JPEG writer
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// void myOutput(unsigned char oneByte) { fputc(oneByte, myFileHandle); } // save byte to file
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// => let's go !
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// TooJpeg::writeJpeg(myOutput, mypixels, 1024, 768);
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#pragma once
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namespace TooJpeg
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{
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// write one byte (to disk, memory, ...)
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typedef void (*WRITE_ONE_BYTE)(unsigned char);
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// this callback is called for every byte generated by the encoder and behaves similar to fputc
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// if you prefer stylish C++11 syntax then it can be a lambda, too:
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// auto myOutput = [](unsigned char oneByte) { fputc(oneByte, output); };
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// output - callback that stores a single byte (writes to disk, memory, ...)
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// pixels - stored in RGB format or grayscale, stored from upper-left to lower-right
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// width,height - image size
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// isRGB - true if RGB format (3 bytes per pixel); false if grayscale (1 byte per pixel)
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// quality - between 1 (worst) and 100 (best)
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// downsample - if true then YCbCr 4:2:0 format is used (smaller size, minor quality loss) instead of 4:4:4, not relevant for grayscale
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// comment - optional JPEG comment (0/NULL if no comment), must not contain ASCII code 0xFF
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bool writeJpeg(WRITE_ONE_BYTE output, const void* pixels, unsigned short width, unsigned short height,
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bool isRGB = true, unsigned char quality = 90, bool downsample = false, const char* comment = nullptr);
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} // namespace TooJpeg
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// My main inspiration was Jon Olick's Minimalistic JPEG writer
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// ( https://www.jonolick.com/code.html => direct link is https://www.jonolick.com/uploads/7/9/2/1/7921194/jo_jpeg.cpp ).
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// However, his code documentation is quite sparse - probably because it wasn't written from scratch and is (quote:) "based on a javascript jpeg writer",
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// most likely Andreas Ritter's code: https://github.com/eugeneware/jpeg-js/blob/master/lib/encoder.js
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//
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// Therefore I wrote the whole lib from scratch and tried hard to add tons of comments to my code, especially describing where all those magic numbers come from.
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// And I managed to remove the need for any external includes ...
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// yes, that's right: my library has no (!) includes at all, not even #include <stdlib.h>
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// Depending on your callback WRITE_ONE_BYTE, the library writes either to disk, or in-memory, or wherever you wish.
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// Moreover, no dynamic memory allocations are performed, just a few bytes on the stack.
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//
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// In contrast to Jon's code, compression can be significantly improved in many use cases:
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// a) grayscale JPEG images need just a single Y channel, no need to save the superfluous Cb + Cr channels
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// b) YCbCr 4:2:0 downsampling is often about 20% more efficient (=smaller) than the default YCbCr 4:4:4 with only little visual loss
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//
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// TooJpeg 1.2+ compresses about twice as fast as jo_jpeg (and about half as fast as libjpeg-turbo).
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// A few benchmark numbers can be found on my website https://create.stephan-brumme.com/toojpeg/#benchmark
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//
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// Last but not least you can optionally add a JPEG comment.
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//
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// Your C++ compiler needs to support a reasonable subset of C++11 (g++ 4.7 or Visual C++ 2013 are sufficient).
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// I haven't tested the code on big-endian systems or anything that smells like an apple.
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//
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// USE AT YOUR OWN RISK. Because you are a brave soul :-)
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