ChromaHash Visual Comparison Report

Cross-Format Comparison

Natural & Realistic Images Only

Format	Avg Size (B)	Encode (ms)	Decode (ms)	Avg ΔE00 ↓	Avg DSSIM ↓	Avg MS-SSIM ↑	Avg PSNR-HVS-M ↑	Avg SSIMULACRA2 ↑	Avg Butteraugli ↓	Avg PSNR (dB) ↑
ChromaHash	32.0	17.879	8.048	8.75	0.2897	0.5132	14.2	-18.8	17.08	19.0
ThumbHash	21.0	0.764	0.219	10.60	0.2989	0.4652	13.2	-34.7	19.77	17.9
BlurHash	36.0	10.440	0.378	13.26	0.3236	0.3903	11.5	-51.1	26.26	16.0
lqip-modern	84.0	2.335	0.000	9.17	0.2521	0.6732	15.9	3.8	11.92	20.4
unpic	592.0	10.466	0.000	N/A	N/A	N/A	N/A	N/A	N/A	N/A

All Images (including synthetic test cases)

Format	Avg Size (B)	Encode (ms)	Decode (ms)	Avg ΔE00 ↓	Avg DSSIM ↓	Avg MS-SSIM ↑	Avg PSNR-HVS-M ↑	Avg SSIMULACRA2 ↑	Avg Butteraugli ↓	Avg PSNR (dB) ↑
ChromaHash	32.0	10.199	7.829	4.33	0.2164	0.6247	26.5	56.9	8.78	30.8
ThumbHash	22.6	0.265	0.226	7.56	0.2316	0.5782	22.7	47.6	14.90	25.9
BlurHash	36.0	3.402	0.337	11.14	0.2788	0.4582	13.6	33.1	21.32	17.6
lqip-modern	75.0	1.374	0.000	4.68	0.1677	0.7721	25.9	63.8	8.65	29.7
unpic	592.0	3.420	0.000	N/A	N/A	N/A	N/A	N/A	N/A	N/A

Methodology

Identical-dimension comparison: every format's decoded preview is Lanczos-3 resampled to the encoder-input (source) resolution and compared against that input, so all formats are scored at the same W×H per image. CIEDE2000 (ΔE00) is the primary metric — color accuracy dominates perceived quality for low-fidelity placeholders, where PSNR correlates poorly. All metrics are computed by iqa-cli (the iqa-rs crate); window-based metrics are omitted (N/A) for images below their minimum size.

Metric	What it measures	Direction
ΔE00 (CIEDE2000)	Primary. Mean perceptual color difference over sRGB→CIELAB (D65)	lower; JND ≈ 1
DSSIM	(1−SSIM)/2; structural fidelity	lower; 0 = identical
MS-SSIM	Multi-scale SSIM	higher; 1 = identical
PSNR-HVS-M	DCT-domain PSNR with CSF + contrast masking (dB)	higher
SSIMULACRA2	Perceptual full-reference score	higher; 100 = identical
Butteraugli	Perceptual distance (libjxl)	lower; 0 = identical
PSNR	Classic pixel MSE metric; penalises intentional LQIP blur	higher; reference only

ΔE00 colour coding: good < 2, warn < 5, bad ≥ 5. DSSIM: good < 0.10, warn < 0.25.

ΔE00 is scored in sRGB against the source's color-managed sRGB appearance, so the cross-format comparison stays apples-to-apples; the gamut-aware ChromaHash matches it while formats that ignore the source gamut look off (higher ΔE00). The Display P3 row's Original and ChromaHash previews are decoded to P3 and tagged with the P3 ICC profile: on a wide-gamut (P3) display they show the true saturated color and match each other, while the sRGB-only formats appear less saturated — ChromaHash renders correctly to the display's gamut.