我提取了一个jpegtran
用于逐字翻转 JPEG 图像(无损)的函数。我已经添加了将文件读入字节数组的代码,我的目标是编写一个函数,该函数在字节数组中获取 JPEG 图像,并在字节数组中返回翻转的 JPEG。源码如下(这是我目前能走的最远的):
#include "libjpeg.h"
#include <stdio.h>
#include <stdlib.h>
void do_flip_v(j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
jvirt_barray_ptr *src_coef_arrays, jvirt_barray_ptr *dst_coef_arrays)
{
/* Vertical flip */
JDIMENSION MCU_rows, comp_height, dst_blk_x, dst_blk_y;
int ci, i, j, offset_y;
JBLOCKARRAY src_buffer, dst_buffer;
JBLOCKROW src_row_ptr, dst_row_ptr;
JCOEFPTR src_ptr, dst_ptr;
jpeg_component_info *compptr;
MCU_rows = dstinfo->image_height / (dstinfo->max_v_samp_factor * DCTSIZE);
for (ci = 0; ci < dstinfo->num_components; ci++) {
compptr = dstinfo->comp_info + ci;
comp_height = MCU_rows * compptr->v_samp_factor;
for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
dst_blk_y += compptr->v_samp_factor) {
dst_buffer = (*srcinfo->mem->access_virt_barray)
((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
(JDIMENSION) compptr->v_samp_factor, TRUE);
if (dst_blk_y < comp_height) {
/* Row is within the mirrorable area. */
src_buffer = (*srcinfo->mem->access_virt_barray)
((j_common_ptr) srcinfo, src_coef_arrays[ci],
comp_height - dst_blk_y - (JDIMENSION)
compptr->v_samp_factor,
(JDIMENSION) compptr->v_samp_factor, FALSE);
}
else {
/* Bottom-edge blocks will be copied verbatim. */
src_buffer = (*srcinfo->mem->access_virt_barray)
((j_common_ptr) srcinfo, src_coef_arrays[ci], dst_blk_y,
(JDIMENSION) compptr->v_samp_factor, FALSE);
}
for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
if (dst_blk_y < comp_height) {
/* Row is within the mirrorable area. */
dst_row_ptr = dst_buffer[offset_y];
src_row_ptr =
src_buffer[compptr->v_samp_factor - offset_y - 1];
for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks;
dst_blk_x++) {
dst_ptr = dst_row_ptr[dst_blk_x];
src_ptr = src_row_ptr[dst_blk_x];
for (i = 0; i < DCTSIZE; i += 2) {
/* copy even row */
for (j = 0; j < DCTSIZE; j++)
* dst_ptr++ = *src_ptr++;
/* copy odd row with sign change */
for (j = 0; j < DCTSIZE; j++)
* dst_ptr++ = - *src_ptr++;
}
}
}
else {
/* Just copy row verbatim. */
jcopy_block_row(src_buffer[offset_y], dst_buffer[offset_y],
compptr->width_in_blocks);
}
}
}
}
}
int main(int argc, char *argv){
FILE *fp = fopen("test.jpg", "r");
fseek(fp, 0, SEEK_END);
int len = ftell(fp);
char *buf = malloc(len);
fseek(fp, 0, SEEK_SET);
fread(buf, 1, len, fp);
fclose(fp);
// calling the flip function.
char *flipped = flip_vertical(buf);
}
(char *) flip_vertical(char *in_stream){
// How to call do_flip_v and return the byte array of the flipped jpeg image?
}
我目前在使用底部的函数flip_vertical时遇到问题,如何调用do_flip_v并返回翻转后的jpeg图像的字节数组?作为 libjpeg 的新手,我已经被折磨了好几天。先感谢您!!!