Hello All,
With JPEG images there are two different types of comments that can be edited within the file metadata:
1. EXIF comments
2. JPEG header comments
EXIF data is an additional set of headers or a wrapper that was added to the original JPEG file specification to accomodate recording information about the device that created the image e.g. digital camera model, exposure settings, etc. They also included a few other fields such as "Comment".
In Windows, when you go to the file properties for a .jpg file and add a comment it is recorded in the EXIF comment field.
However, the original JPEG file specification already had a well defined comment field that Windows seems to have no knowledge of.
Technical note: The JPEG header has a 0xFFFE comment marker followed by a 2-byte length field and then the actual comment.
For various reasons, the JPEG header comments are more reliable from an archival standpoint especially when moving across OS platforms.
There are a variety of programs that will view and edit JPEG header comments such as FastStone Image Viewer or ExifTool.
As of BC version 4.2 the EXIF data is included in JPEG file comparisons and works well.
However, JPEG Header information appears to be ignored in BC comparisons.
As a test, I made a couple copies of an image that had not been edited in any way.
I used FastStone to add a short JPEG header comment to one copy of the image.
I used Win10 File Explorer to add an EXIF comment to another copy.
I then did several BC photo comparisons of the various JPEG files.
The orignal image and the EXIF commented image were flaged as different, with the metadata surprisingly showing many differences including the comment.
Unfortunately, the photo comparison showed the original image and the JPEG header commented image as identical when they clearly are not.
Next, I switched to a Hex compare of the original and the JPEG header commented image and then the difference was clearly indicated.
In summary, am I missing something or can BC be updated to include JPEG header info in it's picture comparison?
Thanks!
With JPEG images there are two different types of comments that can be edited within the file metadata:
1. EXIF comments
2. JPEG header comments
EXIF data is an additional set of headers or a wrapper that was added to the original JPEG file specification to accomodate recording information about the device that created the image e.g. digital camera model, exposure settings, etc. They also included a few other fields such as "Comment".
In Windows, when you go to the file properties for a .jpg file and add a comment it is recorded in the EXIF comment field.
However, the original JPEG file specification already had a well defined comment field that Windows seems to have no knowledge of.
Technical note: The JPEG header has a 0xFFFE comment marker followed by a 2-byte length field and then the actual comment.
For various reasons, the JPEG header comments are more reliable from an archival standpoint especially when moving across OS platforms.
There are a variety of programs that will view and edit JPEG header comments such as FastStone Image Viewer or ExifTool.
As of BC version 4.2 the EXIF data is included in JPEG file comparisons and works well.
However, JPEG Header information appears to be ignored in BC comparisons.
As a test, I made a couple copies of an image that had not been edited in any way.
I used FastStone to add a short JPEG header comment to one copy of the image.
I used Win10 File Explorer to add an EXIF comment to another copy.
I then did several BC photo comparisons of the various JPEG files.
The orignal image and the EXIF commented image were flaged as different, with the metadata surprisingly showing many differences including the comment.
Unfortunately, the photo comparison showed the original image and the JPEG header commented image as identical when they clearly are not.
Next, I switched to a Hex compare of the original and the JPEG header commented image and then the difference was clearly indicated.
In summary, am I missing something or can BC be updated to include JPEG header info in it's picture comparison?
Thanks!
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