u/Pearsonzero

Tested SPDR-processed images against unmodified Kodak PCD0992 originals across JPEG, JPEG XL, AVIF, and WebP at three quality levels each. Results are consistent across all four codec architectures — 46–68% BPP reduction depending on codec and quality level.

These encoders share no implementation code and make independent decisions about how to represent the data they receive — the only common variable is the pixel data entering each pipeline. All encoded outputs, per-image JSON measurements, and verification scripts are in the repo and independently reproducible.

https://github.com/PearsonZero/kodak-pcd0992-multi-codec-compression-response

The repo contains all 24 Kodak PCD0992 images with upstream RGB covariance reshaping applied, both passes through Facebook’s JPEG pipeline showing a 73% mean BPP reduction with stable geometry across recompression, and the unmodified originals for direct comparison.

Measurements are backed by a verification script that reproduces the published numbers independently.

https://github.com/PearsonZero/kodak-pcd0992-spdr-verification-suite

This is my last post on this.

Directional covariance perturbation was applied in standard RGB pixel space upstream of colorspace conversion and encoding. Output files remain ordinary JPEG/TIFF/PNG images readable by existing decoders with no pipeline modification required.

Across 72 perturbations (24 images × 3 channel axes) measured through Facebook’s steady-state JPEG pipeline (FB2), every perturbed Q60 export produced lower output BPP than its corresponding unmodified Q90 original. Mean reduction was 58.1% (range 36.4–87.3%) despite a 7.1× higher output pixel count.

The perturbation disrupted the expected relationship between quality setting and bitrate, producing a consistent collapse of the normal Q-ladder ordering.

Full dataset, manuscript, per-image compression profiles, and measurement scripts:

https://github.com/PearsonZero/kodak-pcd0992-directional-perturbation-compression-response

This dot plot maps the angular distance between image-optimal axes and fixed transform axes across the Kodak Lossless suite. The variance in the chroma rows (SD \approx 15.7°) suggests that "standard" residuals are often far more redundant than we realize.

The two chrominance misalignment angles co-vary at r = 0.999 (R² = 0.999) across all 24 images, ranging from roughly ~22° to ~80° demonstrating that standard BT.601 color axes are rarely "optimal" for any specific image's unique color distribution.

The key data point, labeled kodim14 (a famous image in the set featuring a boat) highlighted in orange, sits slightly below the regression line, representing a minor deviation from the otherwise rigid co-variation of the two axes.

This evidence suggests that when the blue-difference axis (Cb) is misaligned by a certain amount, the red-difference axis (Cr) is almost always misaligned by the exact same proportion. In signal processing terms, this implies that the rotation required to move from standard BT.601 to an image-optimal color space (KLT) is largely consistent across its chrominance plane, even if the magnitude of that rotation changes based on the image content.

This means any regression on angular misalignment only needs one chrominance angle, not two.