做嵌入式图像识别，用V4L2捕获图像为JPEG格式，用IJG JPEG库转成BMP格式时偶尔出现如下错误或警告：
Corrupt JPEG data: XX extraneous bytes before marker 0xXX
或
Corrupt JPEG data: premature end of data segment
由于这些错误在IJG JPEG库里只认为是警告，如果不对其处理，代码将继续执行，因而捕获的图像不正常。这个错误对我的处理算法结果造成影响，决定排除。
Google百度下来发现没有什么好的解决方案，最好的一个是对 Corrupt JPEG data: XX extraneous bytes before marker 0xXX的解决，他是这样做的：
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First, I've noticed that in jpegsrc.v6b.tar.gz there is a file called jerror.h, which has these lines:
JMESSAGE(JWRN_EXTRANEOUS_DATA,
"Corrupt JPEG data: %u extraneous bytes before marker 0x%02x")
Then, I looked for JWRN_EXTRANEOUS_DATA string and found it in jdmarker.c
And then, I commented out the warning line in that file, as below:
if (cinfo->marker->discarded_bytes != 0) {
/*WARNMS2(cinfo, JWRN_EXTRANEOUS_DATA, cinfo->marker->discarded_bytes, c); Commented out by Denny! */
cinfo->marker->discarded_bytes = 0;
}
First, I've noticed that in jpegsrc.v6b.tar.gz there is a file called jerror.h, which has these lines:
JMESSAGE(JWRN_EXTRANEOUS_DATA,
"Corrupt JPEG data: %u extraneous bytes before marker 0x%02x")
Then, I looked for JWRN_EXTRANEOUS_DATA string and found it in jdmarker.c
And then, I commented out the warning line in that file, as below:
if (cinfo->marker->discarded_bytes != 0) {
/*WARNMS2(cinfo, JWRN_EXTRANEOUS_DATA, cinfo->marker->discarded_bytes, c); Commented out by Denny! */
cinfo->marker->discarded_bytes = 0;
}
意思是把WARNMS2（）注掉，然后重新编译IJG JPEG源码，就不会出现Corrupt JPEG data: XX extraneous bytes before marker 0xXX。这个可有点勉强。。。太麻烦了，总应该有好的办法。
Google百度一下 WARNMS2，没有~于是找 JWRN_EXTRANEOUS_DATA，
找到了jerror.h的源码，看到下面有一段：
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#define WARNMS2(cinfo,code,p1,p2)
((cinfo)->err->msg_code = (code),
(cinfo)->err->msg_parm.i[0] = (p1),
(cinfo)->err->msg_parm.i[1] = (p2),
(*(cinfo)->err->emit_message) ((j_common_ptr) (cinfo), -1))
#define WARNMS2(cinfo,code,p1,p2)
((cinfo)->err->msg_code = (code),
(cinfo)->err->msg_parm.i[0] = (p1),
(cinfo)->err->msg_parm.i[1] = (p2),
(*(cinfo)->err->emit_message) ((j_common_ptr) (cinfo), -1))
发现发出的异常消息是emit_message，异常等级为－１, 于是处理掉这个异常就OK了！
代码如下：
先声名一个异常处理函数：my_emit_message
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METHODDEF(void) my_emit_message(j_common_ptr cinfo, int msg_level)
{
my_error_ptr myerr = (my_error_ptr) cinfo->err;
if(msg_level == -1) longjmp(myerr->setjmp_buffer, 1);
}
METHODDEF(void) my_emit_message(j_common_ptr cinfo, int msg_level)
{
my_error_ptr myerr = (my_error_ptr) cinfo->err;
if(msg_level == -1) longjmp(myerr->setjmp_buffer, 1);
}
再捕获这个异常（注意这里没写出其它异常类型处理，如error_exit）：
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struct my_error_mgr jerr;
cinfo.err = jpeg_std_error(&jerr.pub);
jerr.pub.emit_message = my_emit_message;
if (setjmp(jerr.setjmp_buffer) != 0)
{
jpeg_destroy_decompress(&cinfo);//printf("jpeg_destroy_decompress/n");
//...
return 0;
}
struct my_error_mgr jerr;
cinfo.err = jpeg_std_error(&jerr.pub);
jerr.pub.emit_message = my_emit_message;
if (setjmp(jerr.setjmp_buffer) != 0)
{
jpeg_destroy_decompress(&cinfo);//printf("jpeg_destroy_decompress/n");
//...
return 0;
}
这样就解决了，Corrupt JPEG data: XX extraneous bytes before marker 0xXX 问题，不过把所有的emit_message异常都屏蔽了，并认为是失败，代码运行后发现Corrupt JPEG data: premature end of data segment也是其中之一，所以也正好都解决了。代码运行了几分钟很正常，都显示屏蔽了。
这个方法发上来备忘一下，也给需要的人参考。
本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/gzz2424/archive/2010/09/15/5885656.aspx