Refactor OVG to PNG and PNG to OVG converters

- Enhanced `ovg_to_png.py` with improved format detection, including support for both RLE-compressed and raw RGBA formats.
- Added interactive size discovery feature for better dimension detection.
- Updated `png_to_ovg.py` to handle both RLE compression and raw RGBA output formats.
- Expanded README.md to include detailed usage instructions, format descriptions, and examples for both converters.
- Improved error handling and output messages for better user experience.

Author: josephbergdoll

README.md

@@ -1,26 +1,277 @@
-# RCD330 Image Utilities
+# RCD330 Image Utilities: OVG Image Format Converter
 
-Python 3 only because who uses 2 any more? Nerds, that's who. To run these, you need Pillow and numpy. Install via pip:
+This repository contains tools for converting OVG (proprietary image format) files to PNG and back, specifically designed for car stereo firmware modification.
 
-`pip install Pillow numpy`
+## Background
 
-## Tools
+OVG files are a proprietary image format used in the RCD330 (and likely other) car stereo firmware. They use RLE (Run-Length Encoding) compression with RGBA color data, saved to a binary file extension.
 
-### Boot logos
+This project was spun up out of a desire to skin more of the interface than ust the bootlogo. Much credit goes to [@cr3ative](https://github.com/cr3ative/) for sharing his initial discoveries publicly on GitHub in the [RCD 330 Image Utilities repo](https://github.com/cr3ative/rcd_330g_image_utilities).
 
-* To convert an RCD `logo.bin` file to a PNG called `logo.png`, edit and run `python3 rcd_to_png.py`
-* To convert any 800x480 PNG called `logo.png` to RCD `logo.bin`, run `python3 png_to_rcd.py`
+## File Format Description
 
-I haven't yet flashed any results to my personal RCD330. This is a work in progress, but the BIN conversion works both ways and matches exactly the expected format.
+The converter supports two different OVG file formats:
 
-- Credit to `mengxp` for the original image update tarball and conversion utility.
-- Credit to @tef and @marksteward for helping me understand XORs!
+### 1. RLE-Compressed OVG Format
+The traditional OVG format uses RLE (Run-Length Encoding) compression:
+- **Command Block**: 1 byte indicating compression type and pixel count
+- **Pixel Data**: RGBA data (4 bytes per pixel)
+- **RLE Compression**: Efficient encoding for repeated pixels
 
-### OVG bin files (flags, etc)
+### 2. Raw RGBA Format
+Some OVG files contain raw RGBA pixel data without compression:
+- **Direct RGBA**: 4 bytes per pixel (R, G, B, A)
+- **No compression**: Pixel data stored sequentially
+- **Square dimensions**: Often forms perfect or near-perfect squares
 
-* To convert an `_ovg.bin` file to PNG, edit and run `python3 ovg_to_png.py`
-* To convert any PNG to an `_ovg.bin` compatible file, edit and run `python3 png_to_ovg.py`
+The converter automatically detects which format is used and processes accordingly.
 
-- Credit to `Niklas_1414` for pushing me to examine these files. Further credits in the python file.
+### RLE Command Block Format (Format 1 only)
+```
+Bit 7 (MSB): Compression flag (1 = compressed, 0 = uncompressed)
+Bits 6-0: Pixel count - 1 (0-127 representing 1-128 pixels)
+```
 
-Cheers!
+### RLE Compression Types (Format 1 only)
+- **Compressed (MSB = 1)**: Next 4 bytes (RGBA) repeated N times
+- **Uncompressed (MSB = 0)**: Next N×4 bytes are individual RGBA pixels
+
+### Format Auto-Detection
+The converter automatically detects the format by analyzing:
+- **File size**: Must be divisible by 4 for raw RGBA
+- **Dimensions**: Raw RGBA often forms perfect squares
+- **Alpha patterns**: Common alpha values (0, 255) indicate raw RGBA
+
+## Tools Included
+
+### 1. `ovg_to_png.py` - OVG to PNG Decoder
+Converts OVG files to PNG format with transparency preservation.
+
+### 2. `png_to_ovg.py` - PNG to OVG Encoder  
+Converts PNG files back to OVG format with RLE compression.
+
+## Requirements
+
+```bash
+pip3 install --user Pillow
+```
+
+## Usage
+
+### Decoding OVG to PNG
+
+#### Basic Conversion
+```bash
+python3 ovg_to_png.py input.bin [output.png]
+```
+
+Examples:
+```bash
+# Convert with auto-detected dimensions and format
+python3 ovg_to_png.py opt/gresfiles/img_off_clock_face_ovg.bin
+
+# Convert with custom output name
+python3 ovg_to_png.py opt/gresfiles/img_off_clock_face_ovg.bin my_clock_face.png
+
+# The converter will automatically detect if the file is RLE-compressed or raw RGBA
+# Example output:
+# Detected format: raw_rgba
+# Raw RGBA data contains 1521 pixels
+# Auto-detected dimensions: 39x39
+```
+
+#### Specify Exact Dimensions
+```bash
+python3 ovg_to_png.py input.bin output.png --width 286 --height 286
+python3 ovg_to_png.py input.bin --width 200  # Height calculated automatically
+```
+
+#### Interactive Size Discovery
+```bash
+# Use size discovery to find correct dimensions
+python3 ovg_to_png.py input.bin --discover
+
+# Customize discovery range
+python3 ovg_to_png.py input.bin --discover --width-min 50 --width-max 300 --width-step 5
+```
+
+The discovery mode will:
+- Generate test images at different sizes
+- Display each size and wait for your input
+- Let you jump to specific widths
+- Help you find the correct dimensions visually
+
+#### Available Options
+- `-w, --width WIDTH` - Specify image width
+- `--height HEIGHT` - Specify image height  
+- `-d, --discover` - Interactive size discovery mode
+- `--width-min MIN` - Minimum width for discovery (default: 35)
+- `--width-max MAX` - Maximum width for discovery (default: 400)
+- `--width-step STEP` - Width step for discovery (default: 1)
+
+#### Usage Help
+```bash
+python3 ovg_to_png.py
+```
+
+#### Output Files
+- **Clock Face**: 286×286 pixels (perfect square from 81,796 pixels)
+- **Clock Shadow**: 400×400 pixels
+- **Clock Spotlight**: 619×619 pixels  
+- **Clock Hands**: 286×286 pixels each
+
+### Encoding PNG to OVG
+
+#### Convert Specific File
+```bash
+python3 png_to_ovg.py input.png [output.bin]
+```
+
+Examples:
+```bash
+# Convert with custom output name
+python3 png_to_ovg.py my_custom_clock.png img_off_clock_face_ovg_new.bin
+
+# Convert with auto-generated output name (replaces .png with .bin)
+python3 png_to_ovg.py clock_face_decoded.png
+# Creates: clock_face_decoded.bin
+```
+
+#### Usage Help
+```bash
+python3 png_to_ovg.py
+```
+
+Shows usage information and examples.
+
+#### Test Roundtrip Conversion
+```bash
+# Test with default file
+python3 png_to_ovg.py test
+
+# Test with specific file
+python3 png_to_ovg.py test opt/gresfiles/img_off_clock_face_ovg.bin
+```
+
+This will:
+1. Decode the original OVG to PNG
+2. Encode the PNG back to OVG  
+3. Compare file sizes and report compression efficiency
+4. Clean up temporary files automatically
+
+## Complete Workflow for Clock Customization
+
+### Step 1: Extract Original Images
+```bash
+# Extract specific files with custom names
+python3 ovg_to_png.py opt/gresfiles/img_off_clock_face_ovg.bin my_clock_face.png
+python3 ovg_to_png.py opt/gresfiles/img_off_clock_shadow_ovg.bin my_shadow.png
+python3 ovg_to_png.py opt/gresfiles/img_off_clock_spotlight_ovg.bin my_spotlight.png
+
+# Or extract with auto-generated names
+python3 ovg_to_png.py opt/gresfiles/img_off_clock_face_ovg.bin
+# Creates: img_off_clock_face_ovg_decoded.png
+```
+
+### Step 2: Edit Images
+- Open your extracted PNG files in your image editor
+- Modify the clock face design as desired
+- Edit other components (shadow, spotlight, hands) if needed
+- Save as PNG with transparency preserved
+
+### Step 3: Convert Back to OVG
+```bash
+# Convert specific files with custom output names
+python3 png_to_ovg.py my_clock_face.png img_off_clock_face_ovg_new.bin
+python3 png_to_ovg.py my_shadow.png img_off_clock_shadow_ovg_new.bin
+
+# Or convert with auto-generated names
+python3 png_to_ovg.py img_off_clock_face_ovg_decoded.png
+# Creates: img_off_clock_face_ovg_decoded.bin
+```
+
+### Step 4: Replace in Firmware
+- Backup original files first!
+- Replace original `.bin` files with corresponding `*_new.bin` files
+- Update firmware with modified files
+
+## Key Files
+
+### Input Files (Original OVG)
+- `opt/gresfiles/img_off_clock_face_ovg.bin` - Main clock face
+- `opt/gresfiles/img_off_clock_shadow_ovg.bin` - Clock shadow
+- `opt/gresfiles/img_off_clock_spotlight_ovg.bin` - Clock spotlight
+- `opt/gresfiles/img_off_clock_hour_XX_ovg.bin` - Hour hand positions
+- `opt/gresfiles/img_off_clock_minute_XX_ovg.bin` - Minute hand positions
+- `opt/gresfiles/img_off_clock_second_XX_ovg.bin` - Second hand positions
+
+### Output Files (Editable PNG)
+- `clock_face_decoded.png` - Main clock face (286×286)
+- `img_off_clock_*_decoded.png` - Individual components
+
+### Generated Files (New OVG)
+- `img_off_clock_face_ovg_new.bin` - Modified clock face
+- `img_off_clock_*_ovg_new.bin` - Modified components
+
+## Technical Details
+
+### Compression Performance
+Typical compression ratios achieved:
+- **Clock Face**: ~2.8:1 compression
+- **Clock Shadow**: ~10.8:1 compression  
+- **Clock Hands**: ~33-41:1 compression
+- **Spotlight**: ~11.3:1 compression
+
+### Image Specifications
+- **Format**: RGBA (32-bit with alpha channel)
+- **Typical Size**: 286×286 pixels for main components
+- **Color Depth**: 8 bits per channel (R, G, B, A)
+- **Byte Order**: Standard RGBA pixel ordering
+
+## Troubleshooting
+
+### PIL/Pillow Not Found
+```bash
+pip3 install --user Pillow
+```
+
+### File Not Found Errors
+Ensure the `opt/gresfiles/` directory exists with original OVG files.
+
+### Size Mismatch
+The converter automatically calculates optimal dimensions and detects file format. If dimensions appear incorrect:
+
+1. **Check format detection**: The converter will show "Detected format: raw_rgba" or "Detected format: rle_ovg"
+2. **Raw RGBA files**: Should auto-detect to perfect or near-perfect squares
+3. **RLE OVG files**: May require manual dimension specification with `--width` and `--height`
+4. **Use discovery mode**: `--discover` to find correct dimensions visually
+
+### Compression Issues
+If the generated OVG file is significantly larger than the original:
+1. Check for unnecessary transparency in your PNG
+2. Ensure solid color areas are truly solid (no noise/gradients)
+3. The RLE compression works best with areas of repeated pixels
+
+## Development Notes
+
+### Discovery Process
+1. Initial attempts tried standard image formats (BMP, RGB, etc.)
+2. Analyzed byte patterns showing 0xFF padding and RLE-like structures  
+3. Found reference to NXP AN4339 PDF describing similar RLE format
+4. Reverse-engineered the exact command block structure
+5. Implemented both decoder and encoder with roundtrip testing
+
+### Format Insights
+- Files start with 0xFF padding that should be skipped
+- Command blocks use 7-bit pixel counts (1-128 pixels per command)
+- RLE compression is very effective for clock graphics with large solid areas
+- Alpha channel is preserved and properly handled
+
+## References
+
+- [NXP AN4339 Application Note](https://www.nxp.com.cn/docs/en/application-note/AN4339.pdf) - Describes similar RLE routine
+- [Reverse Engineering Stack Exchange](https://reverseengineering.stackexchange.com/questions/27688/open-unknown-image-format-probably-a-raw-image) - Initial format identification
+
+## License
+
+This project is provided as-is for educational and personal use. Always backup original firmware before making modifications.