---
license: apache-2.0
library_name: LiteRT
pipeline_tag: image-segmentation
tags: [litert, tflite, on-device, android, gpu, line-segment-detection, mlsd, wireframe, mobilenetv2]
base_model: navervision/mlsd
---

# M-LSD-tiny — LiteRT (on-device line segment detection, fully-GPU)

[M-LSD](https://github.com/navervision/mlsd) (NAVER, AAAI 2022) light-weight real-time **line segment
detection**, converted to **LiteRT** and running **fully on the `CompiledModel` GPU** (ML Drift) on Android.
Detects straight line segments — building edges, document borders, wireframes, room layout. The **tiny**
variant (MobileNetV2 backbone, 0.62M params) is **1.4 MB** in fp16.

![M-LSD — input | detected line segments (on-device LiteRT GPU)](samples/sample.png)

## On-device (Pixel 8a, Tensor G3 — verified)

| | |
|---|---|
| nodes on GPU | **99 / 99** LITERT_CL (full residency) |
| inference | **~2 ms** (512×512) |
| size | **1.4 MB** (fp16) |
| accuracy | device-vs-PyTorch corr **0.997** (127 vs 128 lines decoded) |

```
image[1,4,512,512] (RGB + ones channel, scaled to [-1,1]) →[GPU: MobileNetV2 U-Net]→ tpMap[1,9,256,256]
```

The output is a "TP map": channel 0 = line-center heatmap, channels 1–4 = start/end displacement. The decode
(sigmoid + 3×3 NMS over centers, displacement → endpoints, ×2) runs on the host.

## How it converts (litert-torch)

Pure CNN encoder-decoder. A single re-authoring: the decoder's `F.interpolate(bilinear, align_corners=True)`
→ **`align_corners=False`** (the Mali delegate bans `align_corners=True` + half-pixel). MobileNetV2 has no
max-pool (strided convs → no `PADV2`), and the upsample is `RESIZE_BILINEAR`, not a transposed conv → fully
GPU-clean. Result: banned ops NONE, all tensors ≤4D, tflite-vs-torch corr **1.0**, device-vs-torch corr **0.997**.

## Preprocessing & decode

Resize to 512×512, append a 4th channel of ones, scale `(x/127.5) - 1`, NCHW. Decode: sigmoid the center map,
3×3 max NMS, threshold (0.10), displacement → endpoints, filter by length, ×2 to 512-space.

## License

[Apache-2.0](https://github.com/navervision/mlsd/blob/main/LICENSE). Upstream:
[navervision/mlsd](https://github.com/navervision/mlsd); PyTorch port [lhwcv/mlsd_pytorch](https://github.com/lhwcv/mlsd_pytorch).