PNG Image Processor

A lightweight C program for reading, processing, and filtering PNG images with support for various convolution kernels and color space conversions.

Features

• PNG Format Support: Read and write PNG files with full chunk parsing

• Multiple Filters: Apply various image processing filters including:

  • Sobel edge detection (X, Y, and combined)
  • Gaussian blur
  • Box blur
  • Laplacian edge detection
  • Image sharpening
  • Image upscaling

• Color Space Conversion: Convert between RGB and grayscale

• Preserves Alpha Channel: Maintains transparency information when processing RGBA images

• Find hidden chunks: Finds not supported chunks other than IHDR, IDAT, IEND

• Write custom chunks: Write your own custom hidden chunks

Requirements

• C compiler (gcc/clang)
• zlib library for PNG compression/decompression
• Standard C libraries (math, stdio, stdlib)

Building

git clone https://github.com/YerdosNar/PNG.git
cd PNG
make

Usage

./png <input.png> -o <output.png> [options]

Options

• -i, --info - Show information about the PNG file
• -o, --output <file> - Output filename (default: out.png)
• -g, --grayscale - Convert to grayscale
• -c, --color - Keep RGB format (default)
• -x, --sobel-x - Apply Sobel X edge detection
• -y, --sobel-y - Apply Sobel Y edge detection
• -s, --sobel - Apply combined Sobel edge detection
• --gaussian [steps] - Apply Gaussian blur
• -b, --blur [steps] - Apply box blur
• -l, --laplacian - Apply Laplacian edge detection
• -sh,--sharpen - Apply sharpening filter
• -u,--upscale [scale_factor] - Apply sharpening filter (Bilinear)
• --none - No filter (default)
• -h, --help - Show help message

Examples

Edge detection with grayscale conversion:

./png photo.png -o edges.png --sobel --grayscale

Apply Gaussian blur:

./png image.png -o blurred.png --gaussian

Sharpen an image:

./png portrait.png -o sharp.png --sharpen

Supported Image Types

• ✅ Grayscale (8-bit)
• ✅ RGB (24-bit)
• ✅ RGBA (32-bit with alpha)
• ✅ Grayscale + Alpha
• ✅ Indexed/Palette images
• ❌ Interlaced PNGs
• ❌ 16-bit depth images

Technical Details

The program implements:

• Full PNG chunk parsing (IHDR, IDAT, IEND)
• All 5 PNG filter types (None, Sub, Up, Average, Paeth)
• 3x3 convolution kernels for image filtering
• Per-channel processing for color images
• Proper PNG CRC calculation and validation

Known Issues

• Currently only supports 8-bit depth images
• Interlaced PNG files are not supported
• Border pixels use simple replication for convolution

Author

YerdosNar 2025.10.17