This is what he says about thumbnails;
//www.impulseadventure.com/photo/fix-corrupt-jpeg-photo.html
Originally posted by article:
"One common misconception people have is that the thumbnail image (that you see in Windows Explorer, for example) is representative of the condition of the actual image data. This is not the case! A JPEG thumbnail mail look perfectly good, but the actual image data could be completely corrupted. That is why you cannot judge whether your files copied OK or are uncorrupted by looking at the preview thumbnail.
Why is this? When your digital camera (or image editor) produces a JPEG file, it creates this in two parts: the first part is your image metadata (EXIF date, time, shooting info, keywords, etc.), which also includes an embedded small thumbnail image. It then creates the second part, the full-size image data, and also stores this into the same file.
JPEG images are almost never corrupted during generation, so both the thumbnail and real image at this point are both fine. However, at some later stage, the file may become damaged (through a copy operation or otherwise), and regions of bytes throughout the file can become erased, overwritten, etc. If this damage occurs to the part of the file that contains the thumbnail, then the thumbnail will be corrupted. If the damage occurs to any of the main image data (scan segment) then the main image will be corrupted. Since the thumbnail section is often less than 2% of the total file size (the rest being the main image data), it is far more likely that the main image will be corrupted but the thumbnail appear fine!" |
If the image data is missing in the main part of the file, then it can't be recovered, IMO. |
