ImageUpscale Pro: SIMD-Accelerated Contrast-Adaptive Image Enhancer in Rust

pub fn apply_adaptive_sharpen(img: &RgbaImage, strength: f32) -> RgbaImage {
    // Clamp strength & compute FidelityFX peak negative cross weight
    let sharpness = strength.clamp(0.0, 1.0);
    let w = -0.125 * sharpness;

    let src_raw = img.as_raw();
    let mut dst_img = RgbaImage::new(width, height);
    let dst_raw = dst_img.as_mut();
    let row_stride = (width * 4) as usize;

    // Process rows in parallel via Rayon: zero lock contention & zero cache thrashing
    dst_raw
        .par_chunks_exact_mut(row_stride)
        .enumerate()
        .for_each(|(y, row_out)| {
            /* 5-Tap cross neighbor gathering: Center, Top, Bottom, Left, Right */
            for c in 0..3 {
                let min_val = center.min(top).min(bottom).min(left).min(right);
                let max_val = center.max(top).max(bottom).max(left).max(right);

                // Dynamic contrast-adaptive amplification factor (prevents ringing)
                let amp = ((min_val / (max_val + 1.0))
                    .min((255.0 - max_val) / (255.0 - min_val + 1.0)))
                    .clamp(0.0, 1.0);
                let peak_w = w * amp;
                let enhanced = (center + peak_w * (top + bottom + left + right)) / (1.0 + 4.0 * peak_w);

                row_out[out_idx + c] = enhanced.clamp(0.0, 255.0).round() as u8;
            }
            row_out[out_idx + 3] = src_raw[center_idx + 3]; // Alpha pass-through
        });
    dst_img
}