JPEG-Repair Manual | Interpreting Error Log Window

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In nosos.jpg I corrupted the header, it is likely it can be repaired using an intact header as entropy looks good. Zeroed.jpg can not be repaired, entropy way too low.

JPEG-Repair Error Log Window

The Error Log Windows gives hints about why a JPEG can not be repaired.

Filesize: The size of the file to be repaired needs to be > 0 bytes as a zero byte file contains no data. No data means that repair is impossible. This may seem obvious but our JPEG Repair Service receives 0 byte files on a regular basis. Such files can not be repaired.

Entropy: Normally this value is between 7.6 and 7.98 for a JPEG file. Other values can have several causes:

  • < 7.60 : The file or a large chunk of the file does not contain JPEG data. Can possibly be repaired, to evaluate send to me + a reference file.
  • > 7.99 : It is very likely the file is encrypted. This is a common issue with JPEGs from Android smart-phones. Technically such files don’t need repair, they need to be decrypted. JPEG-Repair can not decrypt these files.
  • 0.00 : No entropy means the file contains only binary zeros or a repeating byte pattern like FF FF FF FF etc. from start to end. It contains no data at all and can not be repaired.

Last error: If JPEG-Repair runs into an error situation it can trap it will display it in the Last error column. Combine this with the entropy value to draw conclusions.

Example 1: No SOS detected! AND too low entropy. Entropy is always ‘leading’ as it tells us IF the file contains possible JPEG data.

Example 2:  No SOS detected! AND good entropy. Again, entropy is leading. No SOS detected probably means the entire header is lost. It is this SOS JPEG marker JPEG-Repair normally uses to determine where the JPEG bitstream starts.  Although this can not be batch repaired, using the Patch tool you can glue an intact header to the corrupt JPEG file. This technique is for example used to repair certain types of ransomware affected JPEGs. Also: I often see this error occur if people try to repair file that were recovered or undeleted by file recovery of photo recovery software (No SOS detected). These files may simply be incorrectly recovered, try recovering them again using JpegDigger.

List of errors

File access error Can occur already if JPEG-Repair checks the file size. Probably a file rights issue. This is a Windows problem, troubleshoot as such. Check access rights etc..
File open error Can not open file. JPEG-Repair should show you the file name too. This is a Windows problem, troubleshoot as such. Check access rights etc..
File error (target) Can not create (probably) or write to target file. Most likely a Windows issue, troubleshoot as such. My first thought would be to copy the files you want to repair into a folder that it is the root of the drive.
File save error Can not create (probably) or write to target file. Most likely a Windows issue, troubleshoot as such. My first thought would be to copy the files you want to repair into a folder that it is the root of the drive.
No JPEG SOI SOI stands for start of image (marker FF D8). Error is reported if (1) no JPEG header is detected inside a RAW file, or (2) no valid header in reference/sample file or (3) no JPEG header in a file you are trying to open in Patch mode.
Error while parsing JPEG’s go through the parser, which reads the data, interprets it, weeds out corruption, and then saves processed data. The parser is written to cope with corrupted data so normally this error should not occur. If it does it would really help if you could send me the file.
Invalid Markers Invalid JPEG Markers were detected in the JPEG bitstream. JPEG-Repair automatically removes those, however their presence is often a symptom of more wide spread corruption. It is safe to assume the file will look distorted. You’d use the Patch mode to remove such corruption.
Probably no JPEG!

Based on entropy the file does not appear to be a JPEG file. If too high then the file is probably encrypted which is often the case with files from smart-phones. Such files are technically not corrupt, they need to be decrypted which is something JPEG-Repair can not do. If entropy is too low then either the file contains no JPEG data or a large chunk of the data is non JPEG.

0.00 bits/byte entropy? Then JPEG repair can not repair these files.
7.xx bits/byte entropy? Possibly the file contains chunks of JPEG data. To evaluate I need the file + a reference file.

No SOS detected!

SOS stands for Start of Scan (marker FF DA). If JPEG Repair does not detect it, it can not transplant the header of the donor (the sample or reference file) to the patient file in header repair mode because it will not be able to decide where actual image data starts. If entropy looks good (7.6 > < 7.98) you can force the header to be glued to patient file using Patch mode with ‘append’ option checked. This video explains what this very common error means:

However if entropy is 0.00 bits/byte then the file contains no data (zeros or a repeating byte pattern). Such a file can not be repaired by JPEG-Repair or any other software. Unfortunately this is a common issue.

If entropy is 8.00 bits/byte then the data in the patient file is encrypted. Such files are mostly created using Android smart phones. JPEG repair can not repair these files.

Render Error When processing a file with corruption in JPEG bitstream you either see this error or the ‘Invalid Markers’ error. Some times there are so many invalid markers that the component displaying the image in JPEG-Repair can not cope and refuses to show an image at all: Render error.