Filter‐Based Testing

🧪 Panel 5 - Filter-Based Testing

Panel 5 of SubSpectra focuses on visual and pixel-level analysis of images using a wide variety of filters. While not statistical in nature like Chi-square or RS, these effects help visually identify inconsistencies, compression artifacts, or steganographic alterations in LSB layers.

🎨 Filters and Transformations

All filtered images are saved to a folder named:

[original_image_name]_filters

in the same directory as the source image.

✅ Available Filters:

1. Channel Bit Removal (R / G / B / A)

Removes a specific bit layer (0–7) from the chosen channel (Red, Green, Blue, Alpha)
Example filename: image_R_bit_0_removed.png

2. Color Filters

Red, Green, Blue: isolates one channel by zeroing the others
Gray: average of R, G, B to produce grayscale
BW: binary black-and-white using a brightness threshold
Sepia: warm-toned retro effect (based on weighted average formula)

3. Block Averaging Filters

3x3 and 9x9 block average filters replace each pixel with the average color of its neighborhood block
Highlights uniform or noisy areas

4. Special 3x3 Deviation Filter

For every pixel:
- Computes average of surrounding 3x3 block
- If pixel's R / G / B > average → set to 255
- Else → leave unchanged
Emphasizes local anomalies that may suggest manipulation
Saved as: image_special_3x3.png

👁️‍🗨️ Use Case: Visual Forensics

Filters help reveal hidden structure, such as uniform LSB layers
Block filters expose macroblock compression or spatial inconsistencies
BW / Sepia filters emphasize edge changes and unnatural transitions

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📁 Output Folder Structure

Image.png
├── Image_filters/
│   ├── Image_R_bit_0_removed.png
│   ├── Image_G_bit_0_removed.png
│   ├── Image_B_bit_0_removed.png
│   ├── Image_A_bit_0_removed.png
│   ├── Image_R_bit_1_removed.png
│   ├── Image_G_bit_1_removed.png
│   ├── Image_B_bit_1_removed.png
│   ├── Image_A_bit_1_removed.png
......
│   ├── Image_R_bit_7_removed.png
│   ├── Image_G_bit_7_removed.png
│   ├── Image_B_bit_7_removed.png
│   ├── Image_A_bit_7_removed.png
│   ├── Image_red.png
│   ├── Image_gray.png
......
│   ├── Image_3x3.png
│   ├── Image_9x9.png
│   └── Image_special_3x3.png