Color Transformations
Color transformations refer to mathematical operations applied to the color components of an image to modify its appearance, enhance features, or highlight specific information.
Unlike conversions between color models (like RGB to HSI), this section deals with transformations within a color model, such as modifying RGB, HSI, CMY, or CMYK components without changing the model itself.
c) CMY and CMYK Space
For CMY:
For CMYK:
Here, only K (black) is modified to control intensity.
4. Types of Color Transformations
a) Color Complements
- Based on the color circle (color wheel)
- Complementary colors lie opposite each other
- Similar to grayscale negatives: helps reveal hidden details in dark regions
- Example: Complement of red is cyan
Used to enhance or highlight features by inverting the color tones.
b) Color Slicing
- Highlights specific color ranges in an image
- Inspired by intensity slicing from grayscale
- Pixels within the color range are retained
- Pixels outside are mapped to a neutral color (like gray)
Formulas:
Cube-based slicing:
Sphere-based slicing:
c) Tone and Color Corrections
- Corrects over-saturated or under-saturated colors
- Depends on the tone (brightness) of the image:
- High-key: Bright overall
- Low-key: Dark overall
- Middle-key: Balanced
Tone correction spreads pixel intensities more evenly across shadows and highlights.
d) Histogram Processing for Color Images
- Extends grayscale histogram equalization to color
- But: Don’t apply independently to R, G, B, or the color balance may be distorted
- Better: Apply histogram equalization to the intensity (I) component in HSI model