[graphic] libjpeg-turbo/libjpeg-turbo

1. Reference

git hub - https://github.com/libjpeg-turbo/libjpeg-turbo

main page - http://libjpeg-turbo.virtualgl.org/

Describe blog(other person) - http://hanburn.tistory.com/139

example1 - http://stackoverflow.com/questions/9094691/examples-or-tutorials-of-using-libjpeg-turbos-turbojpeg

example2 - http://pingus.seul.org/~grumbel/tmp/libjpeg-test.c

2. libjpge-turbo 란 무엇인가

SIMD instruction을 이용한 JPEG image codec.

 SIMD instruction (MMX, SSE2, NEON, AltiVec)이란?

한국말로 'SIMD 명령어' 라고 하며 Single Instruction Multiple Data의 약자로

병렬 프로세서의 한 종류이다. 즉, 하나의 명령어로 여러 개의 값을 동시에 계산하는 방식이다.

벡터 프로세서에서 많이 사용되는 방식으로, 비디오 게임 콘솔이나 그래픽 카드와 같은 멀티미니더 분야에 자주 사용된다. CPU에서는 인텔의 MMX, 스트리밍 SIMD 확장(SSE)과 AMD의 3D나우! 등의 기술에서 이를 적용했다.

SIMD(wiki) - https://ko.wikipedia.org/wiki/SIMD

MMX(wiki) - https://ko.wikipedia.org/wiki/SIMD

SSE2(wiki) - https://ko.wikipedia.org/wiki/SSE2

 

백터 프로세서(wiki, 참고) - https://ko.wikipedia.org/wiki/%EB%B2%A1%ED%84%B0_%ED%94%84%EB%A1%9C%EC%84%B8%EC%84%9C

크로마 서브샘플링(Chroma subsampling)이란

명도 정보에 비해 색차 정보를 줄여서 영상을 인코딩하는 방식을 말한다.

이론으로는, 원추 세보 600만개, 간상세포 9천만개로 빛보다 색의 구별이 둔감하다 따라서 색감의 정보를 감축시키는 것.

밝기 정보는 루미 컴포넌트라고 하고, 색상에서 명도를 제외한 정보를 색차 컴포넌트라고 한다.

크로마 서브샘플링(wiki) - https://ko.wikipedia.org/wiki/%ED%81%AC%EB%A1%9C%EB%A7%88_%EC%84%9C%EB%B8%8C%EC%83%98%ED%94%8C%EB%A7%81

3. Tutorial

git hub의 sample code - https://github.com/erlyvideo/jpeg/blob/master/c_src/jpeg.c

4. How to do

1) jepg Library on Read file

Step 1. Allocate and initialize JPEG decompression object

Step 2. Specify data source

Step 3. Read file parameters with jpeg_read_header()

Step 4. Set parameters for decompression

Step 5. Start decompressor

Step 6. While (scan lines remain to be read) jpeg_read_scanlines(...)

Step 7. Finish decompression

Step 8. Release JPEG decompression object

#include <stdio.h> #include "jpeglib.h" #include <stddef.h> #include <setjmp.h> //#include <stdlib.h> //#include <string.h> GLOBAL(int) read_JPEG_file(char *filename); struct my_error_mgr { struct jpeg_error_mgr pub; jmp_buf setjmp_buffer; }; typedef struct my_error_mgr * my_error_ptr; void put_scanline_someplace (JSAMPLE* ba, int row_stride) { static int height; int i; for (i=0; i < row_stride; i++) //printf("%d\n", ba[i]); printf ("width: %3d height: %3d\n", row_stride, height++); } METHODDEF(void) my_error_exit (j_common_ptr cinfo) { /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */ my_error_ptr myerr = (my_error_ptr) cinfo->err; /* Always display the message. */ /* We could postpone this until after returning, if we chose. */ (*cinfo->err->output_message) (cinfo); /* Return control to the setjmp point */ longjmp(myerr->setjmp_buffer, 1); } int main(int argc, char *argv[]) { if (argc < 2) { return -1; } read_JPEG_file(argv[1]); return 0; } GLOBAL(int) read_JPEG_file (char * filename) { /* This struct contains the JPEG decompression parameters and pointers to * working space (which is allocated as needed by the JPEG library). */ struct jpeg_decompress_struct cinfo; /* We use our private extension JPEG error handler. * Note that this struct must live as long as the main JPEG parameter * struct, to avoid dangling-pointer problems. */ struct my_error_mgr jerr; /* More stuff */ FILE * infile; /* source file */ JSAMPARRAY buffer; /* Output row buffer */ int row_stride; /* physical row width in output buffer */ /* In this example we want to open the input file before doing anything else, * so that the setjmp() error recovery below can assume the file is open. * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that * requires it in order to read binary files. */ if ((infile = fopen(filename, "rb")) == NULL) { fprintf(stderr, "can't open %s\n", filename); return 0; } /* Step 1: allocate and initialize JPEG decompression object */ /* We set up the normal JPEG error routines, then override error_exit. */ cinfo.err = jpeg_std_error(&jerr.pub); jerr.pub.error_exit = my_error_exit; /* Establish the setjmp return context for my_error_exit to use. */ if (setjmp(jerr.setjmp_buffer)) { /* If we get here, the JPEG code has signaled an error. * We need to clean up the JPEG object, close the input file, and return. */ jpeg_destroy_decompress(&cinfo); fclose(infile); return 0; } /* Now we can initialize the JPEG decompression object. */ jpeg_create_decompress(&cinfo); /* Step 2: specify data source (eg, a file) */ jpeg_stdio_src(&cinfo, infile); /* Step 3: read file parameters with jpeg_read_header() */ (void) jpeg_read_header(&cinfo, TRUE); /* We can ignore the return value from jpeg_read_header since * (a) suspension is not possible with the stdio data source, and * (b) we passed TRUE to reject a tables-only JPEG file as an error. * See libjpeg.txt for more info. */ /* Step 4: set parameters for decompression */ /* In this example, we don't need to change any of the defaults set by * jpeg_read_header(), so we do nothing here. */ //test printf("image width : %d, image height : %d\n", cinfo.image_width, cinfo.image_height); /* Step 5: Start decompressor */ (void) jpeg_start_decompress(&cinfo); /* We can ignore the return value since suspension is not possible * with the stdio data source. */ /* We may need to do some setup of our own at this point before reading * the data. After jpeg_start_decompress() we have the correct scaled * output image dimensions available, as well as the output colormap * if we asked for color quantization. * In this example, we need to make an output work buffer of the right size. */ /* JSAMPLEs per row in output buffer */ row_stride = cinfo.output_width * cinfo.output_components; /* Make a one-row-high sample array that will go away when done with image */ buffer = (*cinfo.mem->alloc_sarray) ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1); /* Step 6: while (scan lines remain to be read) */ /* jpeg_read_scanlines(...); */ /* Here we use the library's state variable cinfo.output_scanline as the * loop counter, so that we don't have to keep track ourselves. */ while (cinfo.output_scanline < cinfo.output_height) { // TODO skip this loop /* jpeg_read_scanlines expects an array of pointers to scanlines. * Here the array is only one element long, but you could ask for * more than one scanline at a time if that's more convenient. */ (void) jpeg_read_scanlines(&cinfo, buffer, 1); /* Assume put_scanline_someplace wants a pointer and sample count. */ put_scanline_someplace(buffer[0], row_stride); } /* Step 7: Finish decompression */ (void) jpeg_finish_decompress(&cinfo); /* We can ignore the return value since suspension is not possible * with the stdio data source. */ /* Step 8: Release JPEG decompression object */ /* This is an important step since it will release a good deal of memory. */ jpeg_destroy_decompress(&cinfo); /* After finish_decompress, we can close the input file. * Here we postpone it until after no more JPEG errors are possible, * so as to simplify the setjmp error logic above. (Actually, I don't * think that jpeg_destroy can do an error exit, but why assume anything...) */ fclose(infile); /* At this point you may want to check to see whether any corrupt-data * warnings occurred (test whether jerr.pub.num_warnings is nonzero). */ /* And we're done! */ return 1; }

$ gcc example.c -ljpeg -o out

$ ./out [file path]

5. Trouble shooting

1) #include "jpeglib.h"에서 size_t, FILE등이 없다고 에러가 나온다.

ex) /usr/include/jpeglib.h:1001:29: error: unknown type name ‘FILE’

- 해결방법 : jpeglib.h보다 stdio.h를 먼저 선언해준다. 

(ref : https://github.com/libjpeg-turbo/libjpeg-turbo/issues/17)

2)