libexif不支持直接加載JPG文件。您需要另外一個包來閱讀JPG文件並提取EXIF文件頭(或者您可以自己寫一些東西)。
注意,在這個例子中它只需創建一個新的EXIF頭,然後將其保存使用fwrite來的文件,然後附加在這裏這部分代碼的不就完了EXIF信息的原始JPG數據:
/* Write JPEG image data, skipping the non-EXIF header */
if (fwrite(image_jpg+image_data_offset, image_data_len, 1, f) != 1) {
fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
goto errout;
}
有一個很好的Github項目叫做exifyay,它使用了libexif,並有兩個額外的庫來處理JPGS中的讀取。這是一個python項目,但庫的來源是C.你可以找到exifyay here(注意我沒有以任何方式與exifyay或libexif)
我剛剛編譯libexif和合並來源exifyay到VS2010項目here。文件夾'contrib \ examples \ LibexifExample'中有一個示例。如果你不喜歡下載隨機鏈接,這裏是我工作的代碼示例:
/*
* write-exif.c
*
* Placed into the public domain by Daniel Fandrich
*
* Create a new EXIF data block and write it into a JPEG image file.
*
* The JPEG image data used in this example is fixed and is guaranteed not
* to contain an EXIF tag block already, so it is easy to precompute where
* in the file the EXIF data should be. In real life, a library like
* libjpeg (included with the exif command-line tool source code) would
* be used to write to an existing JPEG file.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <libexif/exif-data.h>
#include <libjpeg/jpeg-data.h>
#include <JpegEncoderEXIF/JpegEncoderEXIF.h>
/* byte order to use in the EXIF block */
#define FILE_BYTE_ORDER EXIF_BYTE_ORDER_INTEL
/* comment to write into the EXIF block */
#define FILE_COMMENT "libexif demonstration image"
/* special header required for EXIF_TAG_USER_COMMENT */
#define ASCII_COMMENT "ASCII\0\0\0"
static ExifEntry *create_tag(ExifData *exif, ExifIfd ifd, ExifTag tag, size_t len)
{
void *buf;
ExifEntry *entry;
/* Create a memory allocator to manage this ExifEntry */
ExifMem *mem = exif_mem_new_default();
assert(mem != NULL); /* catch an out of memory condition */
/* Create a new ExifEntry using our allocator */
entry = exif_entry_new_mem (mem);
assert(entry != NULL);
/* Allocate memory to use for holding the tag data */
buf = exif_mem_alloc(mem, len);
assert(buf != NULL);
/* Fill in the entry */
entry->data = (unsigned char*)buf;
entry->size = len;
entry->tag = tag;
entry->components = len;
entry->format = EXIF_FORMAT_UNDEFINED;
/* Attach the ExifEntry to an IFD */
exif_content_add_entry (exif->ifd[ifd], entry);
/* The ExifMem and ExifEntry are now owned elsewhere */
exif_mem_unref(mem);
exif_entry_unref(entry);
return entry;
}
int main(int argc, char **argv)
{
ExifEntry *entry;
//Input JPG
char mInputFilename[]="example.jpg";
//Load JPG
JPEGData * mJpegData = jpeg_data_new_from_file(mInputFilename);
//Load Exif data from JPG
ExifData * mExifData = jpeg_data_get_exif_data(mJpegData);
//Set some Exif options
exif_data_set_option(mExifData, EXIF_DATA_OPTION_FOLLOW_SPECIFICATION);
exif_data_set_data_type(mExifData, EXIF_DATA_TYPE_COMPRESSED);
exif_data_set_byte_order(mExifData, FILE_BYTE_ORDER);
entry = create_tag(mExifData, EXIF_IFD_EXIF, EXIF_TAG_USER_COMMENT,
sizeof(ASCII_COMMENT) + sizeof(FILE_COMMENT) - 2);
/* Write the special header needed for a comment tag */
memcpy(entry->data, ASCII_COMMENT, sizeof(ASCII_COMMENT)-1);
/* Write the actual comment text, without the trailing NUL character */
memcpy(entry->data+8, FILE_COMMENT, sizeof(FILE_COMMENT)-1);
/* create_tag() happens to set the format and components correctly for
* EXIF_TAG_USER_COMMENT, so there is nothing more to do. */
/* Create a EXIF_TAG_SUBJECT_AREA tag */
entry = create_tag(mExifData, EXIF_IFD_EXIF, EXIF_TAG_SUBJECT_AREA,
4 * exif_format_get_size(EXIF_FORMAT_SHORT));
entry->format = EXIF_FORMAT_SHORT;
entry->components = 4;
//Write back exif data
jpeg_data_set_exif_data(mJpegData,mExifData);
//Save to JPG
jpeg_data_save_file(mJpegData,"test.jpg");
return 0;
}
10你覺得很難閱讀的鏈接示例的哪一部分?如果你給一些行號,我會看看我能做些什麼。 –
我想,從第263行開始。但當然這是關於寫一個新的標籤。我想要的是編輯現有的標籤。 – anta40