Re: Embedded Thumbnail Not Shown
Posted: Mon Aug 30, 2010 7:09 pm
Hi, 
As I found out, XnView does not require JPEGs to be in the standard-compliant JPEG File Interchange Format (JFIF), in order to read the embedded thumbnail. Several new cameras are producing images missing the APP0 marker, and they all read OK in XnView. However, it does appear that XnView's file parser is not very robust when it comes to ignoring errors. While it does do a good job of reading Exif despite error, apparently it will skip the embedded thumb. So, I think it needs to be able to continue reading and not ignore good data, even if some is not. Obviously, this should only be possible if the file does not contain fatal errors.
Anyway, XnTriq had it right about my image, noting that it had a nonfatal error: Illegal number format 32 for tag 010f. The camera indeed must have a firmware bug that writes the number format as 32 instead of 2 (looks transposed in hex - 0x20 instead of 0x02). Therefore, it causes the Make tag (0x010f) to not be read. If this byte is corrected in a hex editor, then all is well again, and the embedded thumbnail shows. Still, it is hard to believe that this one seemingly unimportant byte in the whole file could halt XnView from scanning for the embedded thumb!
As I found out, XnView does not require JPEGs to be in the standard-compliant JPEG File Interchange Format (JFIF), in order to read the embedded thumbnail. Several new cameras are producing images missing the APP0 marker, and they all read OK in XnView. However, it does appear that XnView's file parser is not very robust when it comes to ignoring errors. While it does do a good job of reading Exif despite error, apparently it will skip the embedded thumb. So, I think it needs to be able to continue reading and not ignore good data, even if some is not. Obviously, this should only be possible if the file does not contain fatal errors.
Anyway, XnTriq had it right about my image, noting that it had a nonfatal error: Illegal number format 32 for tag 010f. The camera indeed must have a firmware bug that writes the number format as 32 instead of 2 (looks transposed in hex - 0x20 instead of 0x02). Therefore, it causes the Make tag (0x010f) to not be read. If this byte is corrected in a hex editor, then all is well again, and the embedded thumbnail shows. Still, it is hard to believe that this one seemingly unimportant byte in the whole file could halt XnView from scanning for the embedded thumb!