Histogram Stretching

Analyze the histogram: Open the histogram display to visualize how pixel values are distributed in your stacked image. Planetary images typically show a narrow spike covering only 10-20% of the available tonal range, leaving most of the 0-65535 (16-bit) range unused.

Identify the data boundaries: Find where your actual image data begins (left edge of the spike) and ends (right edge). Values outside this range are empty - pure black on the left, unused headroom on the right. These boundaries are your starting reference.

Set the black point: Move the black point (shadows slider) to just below where your data begins. This maps the darkest real data to true black. Be careful not to clip shadow detail - the space between planets and sky should remain dark but not crushed to pure black.

Set the white point: Move the white point (highlights slider) to just above where your data ends. This maps your brightest data to white. For planets, the brightest areas are often limb brightening or polar caps - avoid clipping these to pure white.

Apply the initial stretch: With black and white points set, the image contrast expands dramatically. What appeared as a dim, low-contrast disk now shows visible cloud bands, surface features, and color variation. This reveals detail that was always present but invisible.

Adjust the midtones (gamma): Use the midtone slider or gamma control to balance the overall brightness. Moving midtones left brightens the image; moving right darkens it. Find the point where cloud bands and surface features have optimal contrast without crushing shadows.

Apply curves for fine control: For advanced adjustments, use a curves tool. An S-curve increases contrast in the midtones while protecting highlights and shadows. You can target specific tonal ranges - darken the space around the planet or brighten specific features.

Consider CLAHE for local contrast: CLAHE (Contrast Limited Adaptive Histogram Equalization) enhances local contrast independently across image regions. This can reveal subtle variations in cloud bands that global stretching misses. Use modest settings to avoid artificial-looking results.