S
Sproo
I've several times encountered the following with downloaded
jpeg-format images: the image does not preview, or not properly (grey
or garbage at the bottom, as though the file is corrupt or truncated),
but Explorer generates an intact-looking thumbnail version.
Clearly the image data is all there, but with a "frameshift mutation",
"nonsense mutation", or other problem that causes the previewer to
choke or go off the rails partway into the file, while not fazing
whatever code generates the thumbnails.
Unfortunately, the most obvious fix (load it in a proper image-editing
app like photoshop and save it to re-encode it) rarely works. Most of
the damaged images come up garbled in these, sometimes worse than in
Explorer's previewer.
Strangely, it looks like there are three different jpeg decoders in all
this software: a good one in the thumbnail generator that is able to
repair damaged images while reading the file; a basic one in the
previewer; and an outright crummy one in photoshop that is more easily
confused than Explorer's.
The images are clearly recoverable, not just in principle but in
practise; that the thumbnail generator is able to decode the file,
resize it, and generate a thumbnail that looks non-corrupt proves this.
All that is needed is a tool that uses the same method as Explorer's
thumbnail generator to decode and fix images, but then lets you save
the (full-size) image to the name of your choice.
Does anyone know of such a tool? (I presume that most or all images
whose thumbnails look corrupt as well won't be recoverable this way.)
(I'm not being fooled by cached thumbnails -- these are freshly
downloaded files, and I have thumbnail caching disabled anyway;
thumbs.db files can quickly accumulate to consume a full gig(!) or more
of disk space if you work with images a lot, otherwise. Besides, that
would require the image be preexisting on my hard drive, a thumbnail
get cached, and then the image get damaged; I'm not in the habit of
randomly hex-editing my image files.
)
jpeg-format images: the image does not preview, or not properly (grey
or garbage at the bottom, as though the file is corrupt or truncated),
but Explorer generates an intact-looking thumbnail version.
Clearly the image data is all there, but with a "frameshift mutation",
"nonsense mutation", or other problem that causes the previewer to
choke or go off the rails partway into the file, while not fazing
whatever code generates the thumbnails.
Unfortunately, the most obvious fix (load it in a proper image-editing
app like photoshop and save it to re-encode it) rarely works. Most of
the damaged images come up garbled in these, sometimes worse than in
Explorer's previewer.
Strangely, it looks like there are three different jpeg decoders in all
this software: a good one in the thumbnail generator that is able to
repair damaged images while reading the file; a basic one in the
previewer; and an outright crummy one in photoshop that is more easily
confused than Explorer's.
The images are clearly recoverable, not just in principle but in
practise; that the thumbnail generator is able to decode the file,
resize it, and generate a thumbnail that looks non-corrupt proves this.
All that is needed is a tool that uses the same method as Explorer's
thumbnail generator to decode and fix images, but then lets you save
the (full-size) image to the name of your choice.
Does anyone know of such a tool? (I presume that most or all images
whose thumbnails look corrupt as well won't be recoverable this way.)
(I'm not being fooled by cached thumbnails -- these are freshly
downloaded files, and I have thumbnail caching disabled anyway;
thumbs.db files can quickly accumulate to consume a full gig(!) or more
of disk space if you work with images a lot, otherwise. Besides, that
would require the image be preexisting on my hard drive, a thumbnail
get cached, and then the image get damaged; I'm not in the habit of
randomly hex-editing my image files.
)