Using Libjpeg for picture reading

1 Introduction

Libjpeg a picture decoding library, in the project need to read into the picture, but do not want to rely on OPENCV interface, this can libjpeg complete decoding. Libjpeg has two versions, one of the original Libjpeg, the other is Libjpeg-turbo, which is a decoding library using SIMD instruction acceleration, about 3 times times the speed of Libjpeg, code see https://github.com/ Libjpeg-turbo/libjpeg-turbo 2 compile download source code, cmake,nasm reference (https://github.com/libjpeg-turbo/libjpeg-turbo/blob/ MASTER/BUILDING.MD) 3 code decoding module

struct Jpeginfo {unsigned int width;
    unsigned int height;
    ColorType ColorType;
unsigned char* dstimg;
}; /* * Enter picture name, output unsigned char* picture data * */int readjpeg (std::string file_name, jpeginfo &jpeginfo) {struct JPEG_DE
    Compress_struct Cinfo;
    struct My_error_mgr jerr;
    FILE * infile;
    Jsamparray buffer;
    int row_stride;
    errno_t err; if (err = fopen_s (&infile, File_name.c_str (), "RB"))! = 0) {fprintf (stderr, "can ' t open%s\n", file_name
        );
    return-1;
    } Cinfo.err = Jpeg_std_error (&jerr.pub);
    Jerr.pub.error_exit = My_error_exit;
        if (setjmp (Jerr.setjmp_buffer)) {jpeg_destroy_decompress (&cinfo);
        Fclose (infile);
    return-1;
    } jpeg_create_decompress (&cinfo);

    JPEG_STDIO_SRC (&cinfo, infile);

    (void) Jpeg_read_header (&cinfo, TRUE);
    (void) jpeg_start_decompress (&cinfo);

    Row_stride = Cinfo.output_width * cinfo.output_components; int cols= Cinfo.output_width;

    int rows = Cinfo.output_height;


    Buffer = (*cinfo.mem->alloc_sarray) ((j_common_ptr) &cinfo, Jpool_image, Row_stride, 1);
    Jpeginfo.width = Cinfo.output_width;
    Jpeginfo.height = Cinfo.output_height;
        if (cinfo.output_components = = 3) {jpeginfo.colortype = RGB;

    jpeginfo.dstimg = new unsigned char[jpeginfo.width*jpeginfo.height * 3+1];
        }//gray else{jpeginfo.colortype = Gray;
    jpeginfo.dstimg = new unsigned char[jpeginfo.width * jpeginfo.height+1];
        } while (Cinfo.output_scanline < cinfo.output_height) {(void) jpeg_read_scanlines (&cinfo, buffer, 1); for (size_t i = 0; i < cinfo.output_width; i++) {//rgb if (jpeginfo.colortype = = RGB) {jpeginfo.dstimg[(cinfo.output_scanline-1) *jpeginfo.width*3 + i*3] = Buffer[0][i *
                3]; jpeginfo.dstimg[(cinfo.output_scanline-1) *jpeginfo.width*3 + i*3+ 1] = buffer[0][i * 3 + 1];
            jpeginfo.dstimg[(cinfo.output_scanline-1) *jpeginfo.width *3+ i*3 + 2] = buffer[0][i * 3 + 2]; } else if (Jpeginfo.colortype = = Gray) {jpeginfo.dstimg[(Cinfo.output_scanline-
            1) *jpeginfo.width + i] = buffer[0][i];

    }}} (void) jpeg_finish_decompress (&cinfo);
    Jpeg_destroy_decompress (&cinfo);
    Fclose (infile);

return 0; }