Noise Variance Map
Definition
A per-pixel or per-block estimate of local noise variance across an image, computed by filtering out image content with a high-pass or wavelet filter and measuring residual variance. Spatial outliers in the map indicate regions with anomalous noise.
- Type
- Per-pixel or per-block local noise variance estimate
- Method
- High-pass or wavelet filtering, residual variance
- Use
- Flags spatial outliers as forgery indicators
Common questions
What kind of manipulation does a noise variance map reveal?+
It can flag a region pasted in from a different source image, or a region that underwent local processing such as blurring, resizing or recompression, because that region's local noise statistics differ from the surrounding untouched image.
Can a noise variance anomaly alone prove an image was manipulated?+
No, uneven noise can also arise from legitimate in-camera processing applied unevenly across a frame, such as adaptive noise reduction, so an anomaly is a lead for further analysis rather than standalone proof.
Related terms
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