JPEG Medic // Accurate Manual JPEG Recovery
Table of Contents
  1. Overview
  2. Theory of JPEG Repair
    1. JPEG structure
    2. How to fix broken JPEG file
  3. Working with the Program
    1. Main menu
    2. Virtual folder tree
    3. Files panel
    4. Preview panel
    5. Cluster view
    6. Hex view
  4. Repairing JPEG image
    1. Opening JPEG file
    2. Repair window
      1. Menu commands
    3. Repair procedure
      1. Visual analysis and localization of damaged MCUs
      2. Finding the next correct MCU
      3. Deleting damaged MCUs
      4. Inserting empty MCUs
      5. Color correction
        1. Automatic color correction
        2. Manual color correction
      6. Filling empty MCUs with data
        1. Use the thumbnail image to fill the empty MCUs
        2. Auto-generate missing content
    4. Saving repaired JPEG image
    5. Repairing fragmented JPEG file
    6. Repairing damaged JPEG image based on SOS marker
    7. Repairing JPEG file encoded by ransomware

Color correction

Every MCU has a certain assigned value of DC channel coefficients that define the gamma of colors in that MCU. To increase compression rate, the JPEG stream does not store absolute values of these coefficients, but only the difference between the coefficient of the current MCU and the previous one.

When an MCU gets damaged, calculating DC coefficients of the subsequent MCUs becomes impossible, because the reference DC values are now not available. As a result, the colors of the JPEG image after the damaged part become incorrect.

To recover correct color of the image you can use the automatic color correction, or manually recover colors.