How to Use
First of all, you should build and run the sample program shown below. This is a typical usage of TJpgDec module and it helps to narrow down the problem on debugging.
The decompression session is divided in two stages. The first stage is to analyze the JPEG image and the second stage is to decompress it.
- Initialize input stream. (e.g. open a file)
- Allocate JPEG decompression object and work area.
- Call jd_prepare() to analyze and prepare to decompress the JPEG image.
- Initialize output device with the image info in the decompression object.
- Call jd_decomp() to decompress the JPEG image.
System Organization
Example
/*------------------------------------------------*/ /* TJpgDec Quick Evaluation Program for PCs */ /*------------------------------------------------*/ #include <stdio.h> #include <string.h> #include "tjpgd.h" /* Bytes per pixel of image output */ #define N_BPP (3 - JD_FORMAT) /* Session identifier for input/output functions (name, members and usage are as user defined) */ typedef struct { FILE *fp; /* Input stream */ uint8_t *fbuf; /* Output frame buffer */ unsigned int wfbuf; /* Width of the frame buffer [pix] */ } IODEV; /*------------------------------*/ /* User defined input funciton */ /*------------------------------*/ size_t in_func ( /* Returns number of bytes read (zero on error) */ JDEC* jd, /* Decompression object */ uint8_t* buff, /* Pointer to the read buffer (null to remove data) */ size_t nbyte /* Number of bytes to read/remove */ ) { IODEV *dev = (IODEV*)jd->device; /* Session identifier (5th argument of jd_prepare function) */ if (buff) { /* Raad data from imput stream */ return fread(buff, 1, nbyte, dev->fp); } else { /* Remove data from input stream */ return fseek(dev->fp, nbyte, SEEK_CUR) ? 0 : nbyte; } } /*------------------------------*/ /* User defined output funciton */ /*------------------------------*/ int out_func ( /* Returns 1 to continue, 0 to abort */ JDEC* jd, /* Decompression object */ void* bitmap, /* Bitmap data to be output */ JRECT* rect /* Rectangular region of output image */ ) { IODEV *dev = (IODEV*)jd->device; /* Session identifier (5th argument of jd_prepare function) */ uint8_t *src, *dst; uint16_t y, bws; unsigned int bwd; /* Put progress indicator */ if (rect->left == 0) { printf("\r%lu%%", (rect->top << jd->scale) * 100UL / jd->height); } /* Copy the output image rectanglar to the frame buffer */ src = (uint8_t*)bitmap; dst = dev->fbuf + N_BPP * (rect->top * dev->wfbuf + rect->left); /* Left-top of destination rectangular */ bws = N_BPP * (rect->right - rect->left + 1); /* Width of output rectangular [byte] */ bwd = N_BPP * dev->wfbuf; /* Width of frame buffer [byte] */ for (y = rect->top; y <= rect->bottom; y++) { memcpy(dst, src, bws); /* Copy a line */ src += bws; dst += bwd; /* Next line */ } return 1; /* Continue to decompress */ } /*------------------------------*/ /* Program Main */ /*------------------------------*/ int main (int argc, char* argv[]) { JRESULT res; /* Result code of TJpgDec API */ JDEC jdec; /* Decompression object */ void *work; /* Pointer to the work area */ size_t sz_work = 3500; /* Size of work area */ IODEV devid; /* Session identifier */ /* Initialize input stream */ if (argc < 2) return -1; devid.fp = fopen(argv[1], "rb"); if (!devid.fp) return -1; /* Prepare to decompress */ work = (void*)malloc(sz_work); res = jd_prepare(&jdec, in_func, work, sz_work, &devid); if (res == JDR_OK) { /* It is ready to dcompress and image info is available here */ printf("Image size is %u x %u.\n%u bytes of work ares is used.\n", jdec.width, jdec.height, sz_work - jdec.sz_pool); /* Initialize output device */ devid.fbuf = (uint8_t*)malloc(N_BPP * jdec.width * jdec.height); /* Create frame buffer for output image */ devid.wfbuf = jdec.width; res = jd_decomp(&jdec, out_func, 0); /* Start to decompress with 1/1 scaling */ if (res == JDR_OK) { /* Decompression succeeded. You have the decompressed image in the frame buffer here. */ printf("\rDecompression succeeded.\n"); } else { printf("jd_decomp() failed (rc=%d)\n", res); } free(devid.fbuf); /* Discard frame buffer */ } else { printf("jd_prepare() failed (rc=%d)\n", res); } free(work); /* Discard work area */ fclose(devid.fp); /* Close the JPEG file */ return res; }
This option switches the decompression algorithm. How this option affects the performance is highly depends on the processor architectre as shown in right image. The Lv.0 is the basic optimization in minimal memory usage suitable for 8/16-bit processors. The Lv.1 depends on 32-bit barrel shifter and is suitable for 32-bit processors. It requires additional 320 bytes of work area. The Lv.2 enables the table conversion for huffman decoding. It requires additional 6 << HUFF_BITS, 6144 by default, bytes of work area.