Mask Generation
MLX
Safetensors
moonbox
mobilesam
segment-anything
sam
image-segmentation
MobileSAM-MLX / 6bit /mlx_model.py
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6bit build of MobileSAM v2
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"""MobileSAM (ChaoningZhang/MobileSAM, Apache-2.0) in MLX: a port of `mobile_sam` (`build_sam_vit_t`: TinyViT-5M
image encoder + SAM's prompt encoder and mask decoder), the segment-anything half of MobileSAM v2.
import mlx_model
model = mlx_model.load("bf16") # a folder with config.json + model.safetensors
emb = mlx_model.embed(model, rgb) # rgb HxWx3 uint8 -> image embedding (+ sizes)
masks, scores, logits = mlx_model.predict(model, emb, points=[[x, y]], labels=[1], box=None, multimask=True)
`predict` follows SamPredictor.predict: point / box prompts in pixel coordinates of the original image, masks at
the original size (logits > 0), the IoU head's scores, and 256x256 low-res logits. Runs on its own next to its
weights (mlx, numpy, pillow). NHWC; every BatchNorm folded into its conv at conversion.
"""
from __future__ import annotations
import json
from pathlib import Path
import mlx.core as mx
import mlx.nn as nn
import numpy as np
CONFIG = {"model_type": "mobile_sam", "image_size": 1024, "embed_dims": [64, 128, 160, 320], "depths": [2, 2, 6, 2],
"num_heads": [2, 4, 5, 10], "window_sizes": [7, 7, 14, 7], "prompt_dim": 256, "mask_in_chans": 16}
PRECISIONS = ["bf16", "fp16", "8bit", "6bit", "4bit"]
PIXEL_MEAN = np.array([123.675, 116.28, 103.53], np.float32)
PIXEL_STD = np.array([58.395, 57.12, 57.375], np.float32)
GROUP = 64
def quantizable(path: str, module) -> bool:
return isinstance(module, nn.Linear) and module.weight.shape[-1] % GROUP == 0
def resize(x, size):
"""torch F.interpolate(mode="bilinear", align_corners=False), NHWC."""
b, h, w, c = x.shape
oh, ow = int(size[0]), int(size[1])
if (oh, ow) == (h, w):
return x
def axis(n_in, n_out):
s = np.clip((np.arange(n_out, dtype=np.float64) + 0.5) * (n_in / n_out) - 0.5, 0, None)
i0 = np.minimum(np.floor(s).astype(np.int32), n_in - 1)
return mx.array(i0), mx.array(np.minimum(i0 + 1, n_in - 1)), mx.array((s - i0).astype(np.float32))
y0, y1, fy = axis(h, oh)
x0, x1, fx = axis(w, ow)
fy, fx = fy.astype(x.dtype)[None, :, None, None], fx.astype(x.dtype)[None, None, :, None]
top, bot = x[:, y0], x[:, y1]
top = top[:, :, x0] * (1 - fx) + top[:, :, x1] * fx
bot = bot[:, :, x0] * (1 - fx) + bot[:, :, x1] * fx
return top * (1 - fy) + bot * fy
class LayerNorm2d(nn.Module):
"""SAM's channel LayerNorm (eps 1e-6), statistics in float32."""
def __init__(self, c, eps=1e-6):
super().__init__()
self.weight, self.bias, self.eps = mx.ones((c,)), mx.zeros((c,)), eps
def __call__(self, x):
y = x.astype(mx.float32)
u = y.mean(-1, keepdims=True)
s = ((y - u) ** 2).mean(-1, keepdims=True)
return (self.weight * ((y - u) * mx.rsqrt(s + self.eps)).astype(x.dtype) + self.bias)
# ------------------------------------------------------------------------------------------------ TinyViT
def conv(cin, cout, k=1, s=1, p=0, g=1):
return nn.Conv2d(cin, cout, k, stride=s, padding=p, groups=g) # Conv2d_BN, BatchNorm folded
class MBConv(nn.Module):
def __init__(self, c, ratio=4.0):
super().__init__()
h = int(c * ratio)
self.conv1, self.conv2, self.conv3 = conv(c, h), conv(h, h, 3, 1, 1, h), conv(h, c)
def __call__(self, x):
y = nn.gelu(self.conv1(x))
y = nn.gelu(self.conv2(y))
return nn.gelu(self.conv3(y) + x)
class PatchMerging(nn.Module):
def __init__(self, dim, out):
super().__init__()
s = 1 if out in (320, 448, 576) else 2
self.conv1, self.conv2, self.conv3 = conv(dim, out), conv(out, out, 3, s, 1, out), conv(out, out)
def __call__(self, x):
return self.conv3(nn.gelu(self.conv2(nn.gelu(self.conv1(x)))))
class Attention(nn.Module):
def __init__(self, dim, key_dim, heads, res):
super().__init__()
self.heads, self.key_dim, self.scale = heads, key_dim, key_dim ** -0.5
self.norm = nn.LayerNorm(dim)
self.qkv = nn.Linear(dim, 3 * key_dim * heads)
self.proj = nn.Linear(key_dim * heads, dim)
pts = [(i, j) for i in range(res) for j in range(res)]
offs, idx = {}, []
for p1 in pts:
for p2 in pts:
o = (abs(p1[0] - p2[0]), abs(p1[1] - p2[1]))
offs.setdefault(o, len(offs))
idx.append(offs[o])
self.attention_biases = mx.zeros((heads, len(offs)))
self._idx = mx.array(np.array(idx, np.int32).reshape(len(pts), len(pts)))
def __call__(self, x):
b, n, _ = x.shape
qkv = self.qkv(self.norm(x)).reshape(b, n, self.heads, 3 * self.key_dim)
q, k, v = mx.split(qkv, [self.key_dim, 2 * self.key_dim], axis=-1)
q, k, v = (t.transpose(0, 2, 1, 3) for t in (q, k, v))
a = (q @ k.transpose(0, 1, 3, 2)) * self.scale + self.attention_biases[:, self._idx].astype(q.dtype)
a = mx.softmax(a, axis=-1, precise=True)
return self.proj((a @ v).transpose(0, 2, 1, 3).reshape(b, n, -1))
class Mlp(nn.Module):
def __init__(self, dim, hidden):
super().__init__()
self.norm, self.fc1, self.fc2 = nn.LayerNorm(dim), nn.Linear(dim, hidden), nn.Linear(hidden, dim)
def __call__(self, x):
return self.fc2(nn.gelu(self.fc1(self.norm(x))))
class TinyViTBlock(nn.Module):
def __init__(self, dim, heads, ws):
super().__init__()
self.ws = ws
self.attn = Attention(dim, dim // heads, heads, ws)
self.mlp = Mlp(dim, dim * 4)
self.local_conv = conv(dim, dim, 3, 1, 1, dim)
def __call__(self, x):
"""x: (B, H, W, C)."""
b, h, w, c = x.shape
ws = self.ws
if h == ws and w == ws:
y = self.attn(x.reshape(b, h * w, c)).reshape(b, h, w, c)
else:
pb, pr = (ws - h % ws) % ws, (ws - w % ws) % ws
y = mx.pad(x, [(0, 0), (0, pb), (0, pr), (0, 0)]) if pb or pr else x
ph, pw = h + pb, w + pr
y = y.reshape(b, ph // ws, ws, pw // ws, ws, c).transpose(0, 1, 3, 2, 4, 5).reshape(-1, ws * ws, c)
y = self.attn(y)
y = y.reshape(b, ph // ws, pw // ws, ws, ws, c).transpose(0, 1, 3, 2, 4, 5).reshape(b, ph, pw, c)
y = y[:, :h, :w]
x = self.local_conv(x + y)
return x + self.mlp(x.reshape(b, h * w, c)).reshape(b, h, w, c)
class Layer(nn.Module):
def __init__(self, i, dims, depth, heads, ws):
super().__init__()
d = dims[i]
self.blocks = [MBConv(d) for _ in range(depth)] if i == 0 else [TinyViTBlock(d, heads, ws) for _ in range(depth)]
if i < len(dims) - 1:
self.downsample = PatchMerging(d, dims[i + 1])
def __call__(self, x):
for b in self.blocks:
x = b(x)
return self.downsample(x) if "downsample" in self else x
class TinyViT(nn.Module):
def __init__(self, c):
super().__init__()
d = c["embed_dims"]
self.patch_embed = [conv(3, d[0] // 2, 3, 2, 1), conv(d[0] // 2, d[0], 3, 2, 1)]
self.layers = [Layer(i, d, c["depths"][i], c["num_heads"][i], c["window_sizes"][i]) for i in range(4)]
self.neck_conv1 = nn.Conv2d(d[-1], 256, 1, bias=False)
self.neck_norm1 = LayerNorm2d(256)
self.neck_conv2 = nn.Conv2d(256, 256, 3, padding=1, bias=False)
self.neck_norm2 = LayerNorm2d(256)
def __call__(self, x):
x = self.patch_embed[1](nn.gelu(self.patch_embed[0](x)))
for layer in self.layers:
x = layer(x)
return self.neck_norm2(self.neck_conv2(self.neck_norm1(self.neck_conv1(x))))
# ------------------------------------------------------------------------------------------------ SAM decoder
class SAMAttention(nn.Module):
def __init__(self, dim, heads, down=1):
super().__init__()
inner = dim // down
self.heads = heads
self.q_proj, self.k_proj, self.v_proj = nn.Linear(dim, inner), nn.Linear(dim, inner), nn.Linear(dim, inner)
self.out_proj = nn.Linear(inner, dim)
def __call__(self, q, k, v):
q, k, v = self.q_proj(q), self.k_proj(k), self.v_proj(v)
b, nq, c = q.shape
sp = lambda t: t.reshape(b, t.shape[1], self.heads, c // self.heads).transpose(0, 2, 1, 3)
q, k, v = sp(q), sp(k), sp(v)
a = mx.softmax((q @ k.transpose(0, 1, 3, 2)) * (c // self.heads) ** -0.5, axis=-1, precise=True)
return self.out_proj((a @ v).transpose(0, 2, 1, 3).reshape(b, nq, c))
class MLPBlock(nn.Module):
def __init__(self, dim, hidden):
super().__init__()
self.lin1, self.lin2 = nn.Linear(dim, hidden), nn.Linear(hidden, dim)
def __call__(self, x):
return self.lin2(nn.relu(self.lin1(x)))
class TwoWayBlock(nn.Module):
def __init__(self, dim, heads, mlp_dim, skip_pe):
super().__init__()
self.skip_pe = skip_pe
self.self_attn = SAMAttention(dim, heads)
self.cross_attn_token_to_image = SAMAttention(dim, heads, 2)
self.cross_attn_image_to_token = SAMAttention(dim, heads, 2)
self.mlp = MLPBlock(dim, mlp_dim)
self.norm1, self.norm2, self.norm3, self.norm4 = (nn.LayerNorm(dim) for _ in range(4))
def __call__(self, q, k, qpe, kpe):
if self.skip_pe:
q = self.self_attn(q, q, q)
else:
t = q + qpe
q = q + self.self_attn(t, t, q)
q = self.norm1(q)
q = self.norm2(q + self.cross_attn_token_to_image(q + qpe, k + kpe, k))
q = self.norm3(q + self.mlp(q))
k = self.norm4(k + self.cross_attn_image_to_token(k + kpe, q + qpe, q))
return q, k
class TwoWayTransformer(nn.Module):
def __init__(self, dim=256, heads=8, mlp_dim=2048, depth=2):
super().__init__()
self.layers = [TwoWayBlock(dim, heads, mlp_dim, i == 0) for i in range(depth)]
self.final_attn_token_to_image = SAMAttention(dim, heads, 2)
self.norm_final_attn = nn.LayerNorm(dim)
def __call__(self, img, pe, tokens):
b, h, w, c = img.shape
k, kpe, q = img.reshape(b, h * w, c), pe.reshape(b, h * w, c), tokens
for layer in self.layers:
q, k = layer(q, k, tokens, kpe)
q = self.norm_final_attn(q + self.final_attn_token_to_image(q + tokens, k + kpe, k))
return q, k
class MLP(nn.Module):
def __init__(self, din, dh, dout, n):
super().__init__()
dims = [din] + [dh] * (n - 1)
self.layers = [nn.Linear(a, b) for a, b in zip(dims, [dh] * (n - 1) + [dout])]
def __call__(self, x):
for i, l in enumerate(self.layers):
x = nn.relu(l(x)) if i < len(self.layers) - 1 else l(x)
return x
class PromptEncoder(nn.Module):
def __init__(self, dim, emb_hw, img_size, mask_in):
super().__init__()
self.emb_hw, self.img_size = emb_hw, img_size
self.positional_encoding_gaussian_matrix = mx.zeros((2, dim // 2))
self.point_embeddings = [mx.zeros((1, dim)) for _ in range(4)]
self.not_a_point_embed = mx.zeros((1, dim))
self.no_mask_embed = mx.zeros((1, dim))
self.mask_conv1 = nn.Conv2d(1, mask_in // 4, 2, stride=2)
self.mask_norm1 = LayerNorm2d(mask_in // 4)
self.mask_conv2 = nn.Conv2d(mask_in // 4, mask_in, 2, stride=2)
self.mask_norm2 = LayerNorm2d(mask_in)
self.mask_conv3 = nn.Conv2d(mask_in, dim, 1)
def pe(self, coords): # coords in [0, 1], float32
c = (2 * coords - 1) @ self.positional_encoding_gaussian_matrix.astype(mx.float32)
c = 2 * np.pi * c
return mx.concatenate([mx.sin(c), mx.cos(c)], -1)
def dense_pe(self):
h, w = self.emb_hw
ys = (mx.arange(h, dtype=mx.float32) + 0.5) / h
xs = (mx.arange(w, dtype=mx.float32) + 0.5) / w
grid = mx.stack([mx.broadcast_to(xs[None, :], (h, w)), mx.broadcast_to(ys[:, None], (h, w))], -1)
return self.pe(grid)[None] # (1, h, w, C)
def __call__(self, points, labels, box, mask):
dt = self.no_mask_embed.dtype
sparse = []
s = mx.array([self.img_size, self.img_size], dtype=mx.float32)
if points is not None:
pts, lab = points + 0.5, labels
if box is None:
pts = mx.concatenate([pts, mx.zeros((pts.shape[0], 1, 2))], 1)
lab = mx.concatenate([lab, -mx.ones((lab.shape[0], 1))], 1)
e = self.pe(pts / s)
l = lab[..., None]
e = mx.where(l == -1, 0.0, e)
e = e + (l == -1) * self.not_a_point_embed.astype(mx.float32)
e = e + (l == 0) * self.point_embeddings[0].astype(mx.float32)
e = e + (l == 1) * self.point_embeddings[1].astype(mx.float32)
sparse.append(e)
if box is not None:
e = self.pe((box + 0.5).reshape(-1, 2, 2) / s)
e = e + mx.concatenate([self.point_embeddings[2], self.point_embeddings[3]], 0).astype(mx.float32)[None]
sparse.append(e)
sparse = mx.concatenate(sparse, 1).astype(dt)
if mask is not None:
m = nn.gelu(self.mask_norm1(self.mask_conv1(mask)))
dense = self.mask_conv3(nn.gelu(self.mask_norm2(self.mask_conv2(m))))
else:
h, w = self.emb_hw
dense = mx.broadcast_to(self.no_mask_embed.reshape(1, 1, 1, -1), (sparse.shape[0], h, w, self.no_mask_embed.shape[-1]))
return sparse, dense
class MaskDecoder(nn.Module):
def __init__(self, dim=256, n_mask=3):
super().__init__()
self.n = n_mask + 1
self.transformer = TwoWayTransformer(dim)
self.iou_token = mx.zeros((1, dim))
self.mask_tokens = mx.zeros((self.n, dim))
self.up1 = nn.ConvTranspose2d(dim, dim // 4, 2, stride=2)
self.up_norm = LayerNorm2d(dim // 4)
self.up2 = nn.ConvTranspose2d(dim // 4, dim // 8, 2, stride=2)
self.output_hypernetworks_mlps = [MLP(dim, dim, dim // 8, 3) for _ in range(self.n)]
self.iou_prediction_head = MLP(dim, 256, self.n, 3)
def __call__(self, img, pe, sparse, dense):
b = sparse.shape[0]
out = mx.concatenate([self.iou_token, self.mask_tokens], 0)
tokens = mx.concatenate([mx.broadcast_to(out[None], (b,) + out.shape), sparse], 1)
src = mx.broadcast_to(img, (b,) + img.shape[1:]) + dense
pos = mx.broadcast_to(pe, (b,) + pe.shape[1:]).astype(src.dtype)
hs, src = self.transformer(src, pos, tokens)
_, h, w, c = img.shape
up = nn.gelu(self.up2(nn.gelu(self.up_norm(self.up1(src.reshape(b, h, w, c))))))
hyper = mx.stack([self.output_hypernetworks_mlps[i](hs[:, 1 + i]) for i in range(self.n)], 1)
bb, uh, uw, uc = up.shape
masks = (hyper @ up.reshape(b, uh * uw, uc).transpose(0, 2, 1)).reshape(b, self.n, uh, uw)
return masks, self.iou_prediction_head(hs[:, 0])
class Model(nn.Module):
def __init__(self, config: dict = CONFIG):
super().__init__()
self.size = config["image_size"]
e = self.size // 16
self.image_encoder = TinyViT(config)
self.prompt_encoder = PromptEncoder(config["prompt_dim"], (e, e), self.size, config["mask_in_chans"])
self.mask_decoder = MaskDecoder(config["prompt_dim"])
# ------------------------------------------------------------------------------------------------ predictor
def load(folder) -> Model:
folder = Path(folder)
config = json.loads((folder / "config.json").read_text())
model = Model(config)
q = config.get("quantization")
if q:
nn.quantize(model, group_size=q["group_size"], bits=q["bits"], class_predicate=quantizable)
model.load_weights(str(folder / "model.safetensors"), strict=True)
mx.eval(model.parameters())
return model
def dtype(model):
return model.mask_decoder.iou_token.dtype
def embed(model: Model, rgb: np.ndarray) -> dict:
"""SamPredictor.set_image: longest side to 1024 (PIL bilinear), normalize, pad bottom-right, encode."""
from PIL import Image
h, w = rgb.shape[:2]
s = model.size / max(h, w)
nh, nw = int(h * s + 0.5), int(w * s + 0.5)
x = np.asarray(Image.fromarray(rgb).resize((nw, nh), Image.BILINEAR), np.float32)
x = (x - PIXEL_MEAN) / PIXEL_STD
x = np.pad(x, ((0, model.size - nh), (0, model.size - nw), (0, 0)))
feats = model.image_encoder(mx.array(x[None]).astype(dtype(model)))
mx.eval(feats)
return {"features": feats, "original_size": (h, w), "input_size": (nh, nw)}
def predict(model: Model, emb: dict, points=None, labels=None, box=None, multimask=True):
"""SamPredictor.predict: prompts in original-image pixels -> (masks bool (N, H, W), scores (N,), low-res
logits (N, 256, 256))."""
h, w = emb["original_size"]
nh, nw = emb["input_size"]
sx, sy = nw / w, nh / h
pts = lab = bx = None
if points is not None:
pts = mx.array(np.asarray(points, np.float32)[None] * np.array([sx, sy], np.float32))
lab = mx.array(np.asarray(labels, np.float32)[None])
if box is not None:
bx = mx.array(np.asarray(box, np.float32).reshape(1, 4) * np.array([sx, sy, sx, sy], np.float32))
sparse, dense = model.prompt_encoder(pts, lab, bx, None)
pe = model.prompt_encoder.dense_pe()
logits, iou = model.mask_decoder(emb["features"], pe, sparse, dense.astype(sparse.dtype))
sl = slice(1, None) if multimask else slice(0, 1)
logits, iou = logits[:, sl].astype(mx.float32), iou[:, sl].astype(mx.float32)
low = logits
m = resize(logits.transpose(0, 2, 3, 1), (model.size, model.size))[:, :nh, :nw]
m = resize(m, (h, w)).transpose(0, 3, 1, 2)
return np.array(m[0] > 0), np.array(iou[0]), np.array(low[0]), np.array(m[0])
# ------------------------------------------------------------------------------------------------ conversion
def _fold(sd, pre):
"""Conv2d_BN (`pre`.c + `pre`.bn) -> one conv's (weight, bias) in MLX layout."""
w = sd[pre + ".c.weight"].astype(np.float64)
g = sd[pre + ".bn.weight"] / np.sqrt(sd[pre + ".bn.running_var"].astype(np.float64) + 1e-5)
b = sd[pre + ".bn.bias"] - sd[pre + ".bn.running_mean"] * g
return (w * g[:, None, None, None]).astype(np.float32).transpose(0, 2, 3, 1), b.astype(np.float32)
def convert(source: Path) -> dict:
"""runs/source/weights/mobile_sam.pt (a plain state dict) -> MLX names: BatchNorms folded, Sequentials renamed,
the classification head (norm_head / head) dropped."""
import torch
sd = {k: v.float().numpy() for k, v in torch.load(Path(source) / "weights" / "mobile_sam.pt", map_location="cpu",
weights_only=True).items() if v.is_floating_point()}
out = {}
folded = sorted({k[:-len(".c.weight")] for k in sd if k.endswith(".c.weight")})
for pre in folded:
dst = pre.replace("patch_embed.seq.0", "patch_embed.0").replace("patch_embed.seq.2", "patch_embed.1")
out[dst + ".weight"], out[dst + ".bias"] = _fold(sd, pre)
ren = {"image_encoder.neck.0.": "image_encoder.neck_conv1.", "image_encoder.neck.1.": "image_encoder.neck_norm1.",
"image_encoder.neck.2.": "image_encoder.neck_conv2.", "image_encoder.neck.3.": "image_encoder.neck_norm2.",
"prompt_encoder.pe_layer.": "prompt_encoder.",
"prompt_encoder.mask_downscaling.0.": "prompt_encoder.mask_conv1.",
"prompt_encoder.mask_downscaling.1.": "prompt_encoder.mask_norm1.",
"prompt_encoder.mask_downscaling.3.": "prompt_encoder.mask_conv2.",
"prompt_encoder.mask_downscaling.4.": "prompt_encoder.mask_norm2.",
"prompt_encoder.mask_downscaling.6.": "prompt_encoder.mask_conv3.",
"mask_decoder.output_upscaling.0.": "mask_decoder.up1.",
"mask_decoder.output_upscaling.1.": "mask_decoder.up_norm.",
"mask_decoder.output_upscaling.3.": "mask_decoder.up2."}
for k, v in sd.items():
if any(k.startswith(p + ".") for p in folded) or ".head." in k or ".norm_head." in k:
continue
n = k
for a, b in ren.items():
if n.startswith(a):
n = b + n[len(a):]
if n.endswith(".weight") and (n.startswith("prompt_encoder.point_embeddings") or
n.split(".")[-2] in ("not_a_point_embed", "no_mask_embed", "iou_token", "mask_tokens")):
n = n[:-len(".weight")]
if v.ndim == 4:
v = v.transpose(1, 2, 3, 0) if ".up1." in n or ".up2." in n else v.transpose(0, 2, 3, 1)
out[n] = v
return out