jpeg图片提取缩略图代码，包含库文件linux直接编译运行

#include "Jpeg2Thumbnail.h" /* * Here's the routine that will replace the standard error_exit method: */ // 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); // } //读取Jpeg图片的数据并返回，如果出错，返回NULL unsigned char* Jpeg2Thumbnail::ReadJpeg(const char* path, int& width, int& height) { FILE *file = fopen( path, "rb" ); if ( file == NULL ) { return NULL; } struct jpeg_decompress_struct info; //for our jpeg info // struct jpeg_error_mgr err; //the error handler // info.err = jpeg_std_error(&err); // struct my_error_mgr my_err; // info.err = jpeg_std_error(&my_err.pub); // my_err.pub.error_exit = my_error_exit; // /* Establish the setjmp return context for my_error_exit to use. */ // if (setjmp(my_err.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. // */ // printf("Error occured\n"); // jpeg_destroy_decompress(&info); // fclose(file); // return NULL; // } jpeg_create_decompress( &info ); //fills info structure jpeg_stdio_src( &info, file ); //void int ret_Read_Head = jpeg_read_header( &info, 1 ); //int if(ret_Read_Head != JPEG_HEADER_OK){ printf("jpeg_read_header failed\n"); fclose(file); jpeg_destroy_decompress(&info); return NULL; } bool bStart = jpeg_start_decompress( &info ); if(!bStart){ printf("jpeg_start_decompress failed\n"); fclose(file); jpeg_destroy_decompress(&info); return NULL; } int w = width = info.output_width; int h = height = info.output_height; int numChannels = info.num_components; // 3 = RGB, 4 = RGBA unsigned long dataSize = w * h * numChannels; // read RGB(A) scanlines one at a time into jdata[] unsigned char *data = (unsigned char *)malloc( dataSize ); if(!data) return NULL; unsigned char* rowptr; while ( info.output_scanline < h ) { rowptr = data + info.output_scanline * w * numChannels; jpeg_read_scanlines( &info, &rowptr, 1 ); } jpeg_finish_decompress( &info ); fclose( file ); return data; } /*参数为： *返回图片的宽度(w_Dest), *返回图片的高度(h_Dest), *返回图片的位深(bit_depth), *源图片的RGB数据(src), *源图片的宽度(w_Src), *源图片的高度(h_Src) */ unsigned char* Jpeg2Thumbnail::do_Stretch_Linear(int w_Dest,int h_Dest,int bit_depth,unsigned char *src,int w_Src,int h_Src) { int sw = w_Src-1, sh = h_Src-1, dw = w_Dest-1, dh = h_Dest-1; int B, N, x, y; int nPixelSize = bit_depth/8; unsigned char *pLinePrev,*pLineNext; unsigned char *pDest = new unsigned char[w_Dest*h_Dest*bit_depth/8]; unsigned char *tmp; unsigned char *pA,*pB,*pC,*pD; for(int i=0;i<=dh;++i) { tmp =pDest + i*w_Dest*nPixelSize; y = i*sh/dh; N = dh - i*sh%dh; pLinePrev = src + (y++)*w_Src*nPixelSize; //pLinePrev =(unsigned char *)aSrc->m_bitBuf+((y++)*aSrc->m_width*nPixelSize); pLineNext = (N==dh) ? pLinePrev : src+y*w_Src*nPixelSize; //pLineNext = ( N == dh ) ? pLinePrev : (unsigned char *)aSrc->m_bitBuf+(y*aSrc->m_width*nPixelSize); for(int j=0;j<=dw;++j) { x = j*sw/dw*nPixelSize; B = dw-j*sw%dw; pA = pLinePrev+x; pB = pA+nPixelSize; pC = pLineNext + x; pD = pC + nPixelSize; if(B == dw) { pB=pA; pD=pC; } for(int k=0;k<nPixelSize;++k) { *tmp++ = ( unsigned char )( int )( ( B * N * ( *pA++ - *pB - *pC + *pD ) + dw * N * *pB++ + dh * B * *pC++ + ( dw * dh - dh * B - dw * N ) * *pD++ + dw * dh / 2 ) / ( dw * dh ) ); } } } return pDest; } bool Jpeg2Thumbnail::write_JPEG_file (const char * filename, unsigned char* image_buffer, int quality,int image_height, int image_width) { if(filename == NULL || image_buffer == NULL) return false; struct jpeg_compress_struct cinfo; struct jpeg_error_mgr jerr; FILE * outfile; /* target file */ JSAMPROW row_pointer[1]; /* pointer to JSAMPLE row[s] */ int row_stride; /* physical row width in image buffer */ cinfo.err = jpeg_std_error(&jerr); /* Now we can initialize the JPEG compression object. */ jpeg_create_compress(&cinfo); if ((outfile = fopen(filename, "wb")) == NULL) { fprintf(stderr, "can't open %s\n", filename); return false; } jpeg_stdio_dest(&cinfo, outfile); cinfo.image_width = image_width; /* image width and height, in pixels */ cinfo.image_height = image_height; cinfo.input_components = 3; /* # of color components per pixel */ cinfo.in_color_space = JCS_RGB; /* colorspace of input image */ jpeg_set_defaults(&cinfo); jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */); jpeg_start_compress(&cinfo, TRUE); row_stride = image_width * 3; /* JSAMPLEs per row in image_buffer */ while (cinfo.next_scanline < cinfo.image_height) { row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride]; (void) jpeg_write_scanlines(&cinfo, row_pointer, 1); } jpeg_finish_compress(&cinfo); fclose(outfile); jpeg_destroy_compress(&cinfo); return true; } //生成图片的缩略图（图片的一个缩小版本） bool Jpeg2Thumbnail::generate_image_thumbnail(const char* inputFile, const char* outputFile) { if(inputFile == NULL || outputFile == NULL) return false; //读取jpeg图片像素数组 int w=0,h=0; unsigned char* buff = ReadJpeg(inputFile,w,h); if(buff == NULL) { printf("ReadJpeg Failed\n"); return false; } //缩放图片，缩放后的大小为(tb_w,tb_h) //int tb_w = 160, tb_h = 160; int tb_w = 1024, tb_h =1024; unsigned char * img_buf = do_Stretch_Linear(tb_w,tb_h,24,buff,w,h); free(buff); //将缩放后的像素数组保存到jpeg文件 bool bRetWrite = write_JPEG_file(outputFile,img_buf,10,tb_w,tb_h); delete[] img_buf; if(bRetWrite){ return true; }else{ printf("GenerateImageThumbnail: write failed\n"); return true; } } int main() { //unsigned char* ReadJpeg(const char* path, int& width, int& height); Jpeg2Thumbnail jpeg ; system("mkdir bmp"); jpeg.generate_image_thumbnail("2.jpg", "222.jpg"); return 0 ; }