Documentation

LeanMlir.Cam

Class Activation Map (Zhou 2016) — visualization helpers.

The heavy lifts (CAM compute, bilinear upsample, logit recomputation) are in F32Array.lean via FFI. This file provides:

No autodiff is needed — for any network ending in ... → globalAvgPool → dense ic oc act GradCAM collapses to the closed form Zhou et al. computed three years before Selvaraju et al. generalized it.

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def Cam.viridisStops :
Array (UInt8 × UInt8 × UInt8)

21 evenly spaced stops of matplotlib's viridis (perceptually uniform), linearly interpolated by viridis. Hardcoded so we don't carry a runtime dependency on a colormap file.

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    def Cam.viridis (t : Float) :
    UInt8 × UInt8 × UInt8

    Map t ∈ [0, 1] to an RGB triple using a lerped viridis palette. Out-of-range t is clamped to [0, 1].

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      def Cam.overlayHeatmap (imgRGB heat : ByteArray) (H W : Nat) (alpha : Float) :
      ByteArray

      α-blend a heatmap over an RGB image and emit the result as a contiguous [H, W, 3] UInt8 buffer (PPM-ready).

      • imgRGB : already-denormalized [H, W, 3] UInt8 (R, G, B interleaved row-major). Caller is responsible for the ImageNet-mean/std de-normalization for whatever dataset.
      • heat : f32 [H, W] with values in [0, 1].
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        def Cam.writePPM (path : String) (H W : Nat) (pixels : ByteArray) :
        IO Unit

        Write a binary P6 PPM file. pixels is [H, W, 3] UInt8 row-major.

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