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MS-SSIM¶

MS-SSIM (Multi-Scale Structural Similarity Index Measure) extends SSIM to a multi-resolution pyramid, providing a perceptual similarity metric that is robust to viewing distance and display resolution variation. Each scale captures structural information at a different spatial frequency.

Variant¶

The fork ships one CPU MS-SSIM extractor:

Extractor name	Algorithm	Options
`float_ms_ssim`	Floating-point IQA library, 5-scale Gaussian pyramid	`enable_lcs`, `enable_db`, `clip_db`, `enable_chroma`

GPU twins (float_ms_ssim_cuda, float_ms_ssim_sycl, integer_ms_ssim_hip) currently expose only enable_lcs; enable_chroma support for GPU backends is a planned follow-up. (The Vulkan backend was removed in ADR-0726.)

`float_ms_ssim` extractor¶

The extractor uses the IQA library's Gaussian-window floating-point implementation with a 5-scale Laplacian pyramid (Wang et al. 2004). It is the extractor invoked when VMAF model JSON files reference "float_ms_ssim".

The minimum supported input resolution is 176x176. Smaller inputs cause the 5-level pyramid to fall below the 11-tap Gaussian kernel footprint and are rejected with an error at init time (Netflix#1414 / ADR-0153).

Output features¶

Feature name	Description	Condition
`float_ms_ssim`	MS-SSIM on the luma (Y) plane	Always
`float_ms_ssim_cb`	MS-SSIM on the Cb (U) chroma plane	`enable_chroma=true` only
`float_ms_ssim_cr`	MS-SSIM on the Cr (V) chroma plane	`enable_chroma=true` only
`float_ms_ssim_l_scale0-4`	Per-scale luminance component	`enable_lcs=true`, luma only
`float_ms_ssim_c_scale0-4`	Per-scale contrast component	`enable_lcs=true`, luma only
`float_ms_ssim_s_scale0-4`	Per-scale structure component	`enable_lcs=true`, luma only

Options¶

enable_chroma (bool, default false): emit per-plane _cb and _cr scores in addition to luma. YUV400P sources are always luma-only.
enable_lcs (bool, default false): emit per-scale luminance, contrast, and structure intermediate components for the luma plane.
enable_db (bool, default false): report the luma MS-SSIM score as dB (-10 * log10(1 - score)).
clip_db (bool, default false): clip the dB score at the theoretical peak. Only meaningful when enable_db=true.

How to run¶

# Luma-only MS-SSIM (default)
core/build/tools/vmaf \
    --reference ref.yuv --distorted dist.yuv \
    --width 1920 --height 1080 --pixel_format 420 --bitdepth 8 \
    --no_prediction --feature float_ms_ssim --output /dev/stdout

# Per-channel MS-SSIM (luma + Cb + Cr)
core/build/tools/vmaf \
    --reference ref.yuv --distorted dist.yuv \
    --width 1920 --height 1080 --pixel_format 420 --bitdepth 8 \
    --no_prediction --feature 'float_ms_ssim:enable_chroma=true' --output /dev/stdout

See also¶

SSIM - single-scale structural similarity
SSIMULACRA2 - perceptually tuned alternative