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Enhance Images

Enhance Images

When browsing your library in the File Manager or Collection, select Enhance Images from the folder menu to optimize visual clarity across all comic issues in that directory.

Older digital comic releases and vintage print scans can suffer from washed-out colors, elevated black levels, and dull contrast. The Enhance Images tool processes all images within each CBZ archive in the directory, improving readability while preserving subtle artistic details. This operation does not traverse subdirectories.

Visual Comparison

Before After
Enhance Before Enhance After

Enhancement Algorithm

Rather than applying a simple linear contrast adjustment — which risks blowing out paper highlights or clipping dark textures — CLU applies an intelligent modified S-curve adjustment using Python's Pillow (PIL) library.

Modified S-Curve LUT

  • Dark Tones (< 128 brightness): Receives the full S-curve adjustment, deepening muddy darks into rich blacks.
  • Bright Tones (≥ 128 brightness): Progressively blends the original pixel values with the curve, ensuring bright backgrounds, white panels, and text balloons do not get blown out.
  • Mid-Tones: Boosts color saturation and ink line sharpness without introducing harsh artifacts.
def modified_s_curve_lut():
    lut = []
    for i in range(256):
        # Calculate base S-curve value using cosine
        s = 0.5 - 0.5 * math.cos(math.pi * (i / 255))
        s_val = 255 * s
        # Apply full curve below 128; blend smoothly with original above 128
        if i < 128:
            blend = 0.0
        else:
            blend = (i - 128) / (255 - 128)
        new_val = (1 - blend) * s_val + blend * i
        lut.append(int(round(new_val)))
    return lut

Color Space Adaptability

The enhancement pipeline inspects each image's color space before applying the transformation:

  • Grayscale (L): Applies the 256-value lookup table directly to the luminance channel.
  • RGB Color (RGB): Replicates and applies the LUT across all three color channels simultaneously.
  • Alpha Transparency (RGBA): Splits color and alpha channels, applies the LUT to red, green, and blue channels, and recombines them while preserving alpha transparency intact.