An image processing library implemented in pure-C

About

Ocular is a library for common and advanced image processing algorithms, without the use of any external dependencies. Suggestions for new features are welcome.

Note: RGBA byte-order is expected for all pixel data.

Documentation

The documentation of the exported functions along with examples can be found at Library Documentation.

Features

Color Adjustment Filters

Basic Adjustments

• Average Luminance Threshold
• Brightness/Contrast
• Exposure
• Equalize
• Gamma
• Histogram Stretch (contrast stretching)
• Levels
• Luminance Threshold (like Photoshop Threshold)

Color Balance & Tone

• Color Balance
• Color Invert
• Color Temperature
• Color Matrix
• Channel Mixer
• Curves
• False Color (mix between two colors using luminance)
• Grayscale (desaturate)
• Highlight/Shadow/Tint
• Hue
• HSL
• Levels
• Monochrome
• RGB
• Saturation
• Sepia
• Skin Tone
• Split Toning
• Vibrance
• White Balance

Lighting Correction

• Haze (add/remove)
• Haze Removal (Dark Channel Prior)
• Retinex (Multi-Scale with Color Restoration)
• Backlight Repair (corrects extremely low or non-uniform lighting)
• Highlight/Shadow

Specialized Color Processing

• Lookup (Remap Colors/LUT)
• Chroma Key (Color Key / Remove Specific Color)
• Posterize
• Palettize
  • from file (remaps colors to closest color in palette file with optional dithering)
  • from image (reduces unique colors using color quantization with optional dithering)

Compositing & Blending

• Opacity
• Image Blending (supports 27 Photoshop modes)

🧠 Automatic Enhancements

• Auto Contrast
• Auto Gamma Correction
• Auto Level
• Auto White Balance
• Auto Threshold

Image Processing Filters

Blur/De-noise

• Average (Mean) Blur
• BEEPS (Bi-exponential Edge-preserving Smoothing)
• Bilateral (selectively blurs preserving edges and other details)
• Box Blur
• Exponential Blur
• Gaussian Blur
• Guided Filter
• Median Blur
• Motion Blur
• Radial Blur
• Surface Blur
• Skin Smoothing
• Zoom Blur

Morphology

• Erode/Dilate
• High Pass
• Min/Max
• Skeletonize (thinning)

Sharpening

• Sharpen
• Unsharp Mask

Edge Detection

• Canny Edge
• Gradient Edge
• Laplacian Edge (Laplacian of Gaussian)
• Prewitt Edge
• Roberts Edge
• Sobel Edge

Stylize/Artistic

• Frosted Glass
• Film Grain
• Glass Tiles
• Marble
• Kuwahara
• Oil Paint
• Portrait Glow
• Relief (Emboss)

Pixelate

• Color Halftone
• Crystallize
• Fragment
• Mosaic
• Pointillize

Distortion

• Kaleidoscope
• Pinch
• Polar Coordinates
• Ripple
• Spherize
• Twirl
• Wave

Render

• Clouds

OCR Pre-preprocessing

• Despeckle (Salt & Pepper Noise Removal)
• Deskewing
• Skeletonize (thinning)

Misc

• 2D Convolution
• Resampling (resize) [Nearest-neighbor, bilinear, bicubic and lanzcos]
• Image Blending (supports 27 Photoshop modes)
• FFT (Fast Fourier Transform) [Low-pass, high-pass, band-pass, band-stop, custom]
• FFT Visualization (outputs frequency domain)

General

• Retrieve average image luminosity
• Retrieve average color
• Retrieve image size
• Crop
• Flip (Vertical/Horizontal)
• Rotate image (bilinear and bicubic)
• Hough transform line detection

Color Quantization

• Median Cut, Octree

Dithering

• Ordered Bayer (4x4 and 8x8), Atkinson, Burkes, Sierra, Sierra Two-Row, Sierra Lite, Stucki, Jarvis-Judice-Ninke, Single Neighbor, Floyd-Steinberg

Color Space Conversion

Note: These are primarly used for included filters and added on as needed basis.

• RGB <--> YIQ
• RGB <--> HSL
• RGB <--> HSV
• RGB <--> YCbCr
• RGB <--> CMYK
• RGB <--> CIELab

Palettes

File Extension	Name	Read	Write
.aco	Adobe Color Swatch	✓	✓*
.act	Adobe Color Table	✓	✓
.ase	Adobe Swatch Exchange	✓
.gpl	GIMP Palette	✓	✓
.pal, .psppalette	Paint Shop Pro Palette	✓	✓
.pal	Microsoft RIFF Palette	✓	✓
.txt	Paint.NET Palette	✓	✓

NOTE: *RGB only.

Running

To compile the library, simply do the following:

cmake .
make

This will out the following 4 files:

• static library lib\libocular.xxx
• dynamic link library bin\ocular.dll
• cli image demo bin\demo.exe
• cli palette demo bin\palette.exe

Licensing

Ocular is under the MIT license.

See the LICENSE file for details.