diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ad8a148
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+__pycache__/
+train.py
\ No newline at end of file
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..e69de29
diff --git a/demo.py b/demo.py
new file mode 100644
index 0000000..1579e7e
--- /dev/null
+++ b/demo.py
@@ -0,0 +1,31 @@
+import torch
+from PIL import Image
+from torchvision import transforms
+from model import CheckerboardAutogressive
+
+torch.backends.cudnn.deterministic = True
+
+if __name__ == '__main__':
+    device = 'cuda' if torch.cuda.is_available() else 'cpu'
+    checkpoint = torch.load('checkpoint.pth.tar', map_location=device)
+
+    net = CheckerboardAutogressive().to(device).eval()
+    net.load_state_dict(checkpoint["state_dict"])
+
+    img = Image.open('./images/kodim01.png').convert('RGB')
+    x = transforms.ToTensor()(img).unsqueeze(0).to(device)
+
+    with torch.no_grad():
+        # codec
+        out = net.compress(x)
+        rec = net.decompress(out['strings'], out['shape'])
+        rec = transforms.ToPILImage()(rec['x_hat'].squeeze().cpu())
+        rec.save('./images/codec.png', format="PNG")
+
+        # inference        
+        out = net(x)
+        rec = out['x_hat'].clamp(0, 1)
+        rec = transforms.ToPILImage()(rec.squeeze().cpu())
+        rec.save('./images/infer.png', format="PNG")
+
+        print('saved in ./images')
diff --git a/images/codec.png b/images/codec.png
new file mode 100644
index 0000000..4836e07
Binary files /dev/null and b/images/codec.png differ
diff --git a/images/infer.png b/images/infer.png
new file mode 100644
index 0000000..2d2a92b
Binary files /dev/null and b/images/infer.png differ
diff --git a/images/kodim01.png b/images/kodim01.png
new file mode 100644
index 0000000..14317f0
Binary files /dev/null and b/images/kodim01.png differ
diff --git a/layers/__init__.py b/layers/__init__.py
new file mode 100644
index 0000000..09ad170
--- /dev/null
+++ b/layers/__init__.py
@@ -0,0 +1 @@
+from .layers import *
\ No newline at end of file
diff --git a/layers/layers.py b/layers/layers.py
new file mode 100644
index 0000000..cabd4c5
--- /dev/null
+++ b/layers/layers.py
@@ -0,0 +1,41 @@
+from typing import Any
+
+import torch
+import torch.nn as nn
+
+from torch import Tensor
+
+
+class CheckerboardMaskedConv2d(nn.Conv2d):
+    """
+    if kernel_size == (5, 5)
+    then mask:
+        [[0., 1., 0., 1., 0.],
+         [1., 0., 1., 0., 1.],
+         [0., 1., 0., 1., 0.],
+         [1., 0., 1., 0., 1.],
+         [0., 1., 0., 1., 0.]]
+    0: non-anchor
+    1: anchor
+    """
+    def __init__(self, *args: Any, **kwargs: Any):
+        super().__init__(*args, **kwargs)
+
+        self.register_buffer("mask", torch.zeros_like(self.weight.data))
+
+        self.mask[:, :, 0::2, 1::2] = 1
+        self.mask[:, :, 1::2, 0::2] = 1
+
+    def forward(self, x: Tensor) -> Tensor:
+        # TODO: weight assigment is not supported by torchscript
+        self.weight.data *= self.mask
+        return super().forward(x)
+
+
+if __name__ == '__main__':
+
+    # notice that the bias is 'True' in practice
+    ckbd = CheckerboardMaskedConv2d(3, 3, kernel_size=5, padding=2, stride=1, bias=True)
+    x = torch.rand((1, 3, 8, 8))
+
+    print(ckbd(x))
\ No newline at end of file
diff --git a/model.py b/model.py
new file mode 100644
index 0000000..159f605
--- /dev/null
+++ b/model.py
@@ -0,0 +1,150 @@
+import torch
+
+from compressai.models.google import JointAutoregressiveHierarchicalPriors
+from layers import CheckerboardMaskedConv2d
+from modules import Demultiplexer, Multiplexer
+
+class CheckerboardAutogressive(JointAutoregressiveHierarchicalPriors):
+    def __init__(self, N=192, M=192, **kwargs):
+        super().__init__(N, M, **kwargs)
+
+        self.context_prediction = CheckerboardMaskedConv2d(
+            M, 2 * M, kernel_size=5, padding=2, stride=1
+        )
+
+    def forward(self, x):
+        y = self.g_a(x)
+        z = self.h_a(y)
+        z_hat, z_likelihoods = self.entropy_bottleneck(z)
+        params = self.h_s(z_hat)
+
+        y_hat = self.gaussian_conditional.quantize(
+            y, "noise" if self.training else "dequantize"
+        )
+
+        # set non_anchor to 0
+        y_half = y_hat.clone()
+        y_half[:, :, 0::2, 0::2] = 0
+        y_half[:, :, 1::2, 1::2] = 0
+
+        # set anchor's ctx to 0, otherwise there will be a bias
+        ctx_params = self.context_prediction(y_half)
+        ctx_params[:, :, 0::2, 1::2] = 0
+        ctx_params[:, :, 1::2, 0::2] = 0
+
+        gaussian_params = self.entropy_parameters(
+            torch.cat((params, ctx_params), dim=1)
+        )
+        scales_hat, means_hat = gaussian_params.chunk(2, 1)
+        _, y_likelihoods = self.gaussian_conditional(y, scales_hat, means=means_hat)
+        x_hat = self.g_s(y_hat)
+
+        return {
+            "x_hat": x_hat,
+            "likelihoods": {"y": y_likelihoods, "z": z_likelihoods},
+        }
+
+    def compress(self, x):
+        y = self.g_a(x)
+        z = self.h_a(y)
+
+        z_strings = self.entropy_bottleneck.compress(z)
+        z_hat = self.entropy_bottleneck.decompress(z_strings, z.size()[-2:])
+
+        params = self.h_s(z_hat)
+
+        # Notion: in compressai, the means must be subtracted before quantification.
+        # In order to get y_half, we need subtract y_anchor's means and then quantize,
+        # to get y_anchor's means, we have to go through 'gep' here
+        N, _, H, W = z_hat.shape
+        zero_ctx_params = torch.zeros([N, 2 * self.M, H * 4, W * 4]).to(z_hat.device)
+        gaussian_params = self.entropy_parameters(
+            torch.cat((params, zero_ctx_params), dim=1)
+        )
+        _, means_hat = gaussian_params.chunk(2, 1)
+        y_hat = self.gaussian_conditional.quantize(y, "dequantize", means=means_hat)
+
+        # set non_anchor to 0
+        y_half = y_hat.clone()
+        y_half[:, :, 0::2, 0::2] = 0
+        y_half[:, :, 1::2, 1::2] = 0
+
+        # set anchor's ctx to 0, otherwise there will be a bias
+        ctx_params = self.context_prediction(y_half)
+        ctx_params[:, :, 0::2, 1::2] = 0
+        ctx_params[:, :, 1::2, 0::2] = 0
+
+        gaussian_params = self.entropy_parameters(
+            torch.cat((params, ctx_params), dim=1)
+        )
+
+        scales_hat, means_hat = gaussian_params.chunk(2, 1)
+
+        y_anchor, y_non_anchor = Demultiplexer(y)
+        scales_hat_anchor, scales_hat_non_anchor = Demultiplexer(scales_hat)
+        means_hat_anchor, means_hat_non_anchor = Demultiplexer(means_hat)
+
+        indexes_anchor = self.gaussian_conditional.build_indexes(scales_hat_anchor)
+        indexes_non_anchor = self.gaussian_conditional.build_indexes(scales_hat_non_anchor)
+
+        anchor_strings = self.gaussian_conditional.compress(y_anchor, indexes_anchor, means=means_hat_anchor)
+        non_anchor_strings = self.gaussian_conditional.compress(y_non_anchor, indexes_non_anchor, means=means_hat_non_anchor)
+
+        return {
+            "strings": [anchor_strings, non_anchor_strings, z_strings],
+            "shape": z.size()[-2:],
+        }
+    
+    def decompress(self, strings, shape):
+        """
+        See Figure 5. Illustration of the proposed two-pass decoding.
+        """
+        assert isinstance(strings, list) and len(strings) == 3
+        z_hat = self.entropy_bottleneck.decompress(strings[2], shape)
+        params = self.h_s(z_hat)
+
+        # PASS 1: anchor
+        N, _, H, W = z_hat.shape
+        zero_ctx_params = torch.zeros([N, 2 * self.M, H * 4, W * 4]).to(z_hat.device)
+        gaussian_params = self.entropy_parameters(
+            torch.cat((params, zero_ctx_params), dim=1)
+        )
+
+        scales_hat, means_hat = gaussian_params.chunk(2, 1)
+        scales_hat_anchor, _ = Demultiplexer(scales_hat)
+        means_hat_anchor, _ = Demultiplexer(means_hat)
+
+        indexes_anchor = self.gaussian_conditional.build_indexes(scales_hat_anchor)
+        y_anchor = self.gaussian_conditional.decompress(strings[0], indexes_anchor, means=means_hat_anchor)     # [1, 384, 8, 8]
+        y_anchor = Multiplexer(y_anchor, torch.zeros_like(y_anchor))    # [1, 192, 16, 16]
+        
+        # PASS 2: non-anchor
+        ctx_params = self.context_prediction(y_anchor)
+        gaussian_params = self.entropy_parameters(
+            torch.cat((params, ctx_params), dim=1)
+        )
+
+        scales_hat, means_hat = gaussian_params.chunk(2, 1)
+        _, scales_hat_non_anchor = Demultiplexer(scales_hat)
+        _, means_hat_non_anchor = Demultiplexer(means_hat)
+
+        indexes_non_anchor = self.gaussian_conditional.build_indexes(scales_hat_non_anchor)
+        y_non_anchor = self.gaussian_conditional.decompress(strings[1], indexes_non_anchor, means=means_hat_non_anchor)     # [1, 384, 8, 8]
+        y_non_anchor = Multiplexer(torch.zeros_like(y_non_anchor), y_non_anchor)    # [1, 192, 16, 16]
+
+        # gather
+        y_hat = y_anchor + y_non_anchor
+        x_hat = self.g_s(y_hat).clamp_(0, 1)
+
+        return {
+            "x_hat": x_hat,
+        }
+
+
+if __name__ == "__main__":
+    x = torch.randn([1, 3, 256, 256])
+    model = CheckerboardAutogressive()
+    model.update(force=True)
+
+    out = model.compress(x)
+    rec = model.decompress(out["strings"], out["shape"])
diff --git a/modules/__init__.py b/modules/__init__.py
new file mode 100644
index 0000000..9a8067b
--- /dev/null
+++ b/modules/__init__.py
@@ -0,0 +1 @@
+from .modules import *
\ No newline at end of file
diff --git a/modules/modules.py b/modules/modules.py
new file mode 100644
index 0000000..9c0f849
--- /dev/null
+++ b/modules/modules.py
@@ -0,0 +1,79 @@
+from turtle import forward
+import torch.nn as nn
+import torch
+
+
+class Space2Depth(nn.Module):
+    """
+    ref: https://github.com/huzi96/Coarse2Fine-PyTorch/blob/master/networks.py
+    """
+
+    def __init__(self, r=2):
+        super().__init__()
+        self.r = r
+
+    def forward(self, x):
+        r = self.r
+        b, c, h, w = x.size()
+        out_c = c * (r**2)
+        out_h = h // r
+        out_w = w // r
+        x_view = x.view(b, c, out_h, r, out_w, r)
+        x_prime = x_view.permute(0, 3, 5, 1, 2, 4).contiguous().view(b, out_c, out_h, out_w)
+        return x_prime
+
+
+class Depth2Space(nn.Module):
+    def __init__(self, r=2):
+        super().__init__()
+        self.r = r
+
+    def forward(self, x):
+        r = self.r
+        b, c, h, w = x.size()
+        out_c = c // (r**2)
+        out_h = h * r
+        out_w = w * r
+        x_view = x.view(b, r, r, out_c, h, w)
+        x_prime = x_view.permute(0, 3, 4, 1, 5, 2).contiguous().view(b, out_c, out_h, out_w)
+        return x_prime
+
+
+def Demultiplexer(x):
+    """
+    See Supplementary Material: Figure 2
+    """
+    x_prime = Space2Depth(r=2)(x)
+    
+    _, C, _, _ = x_prime.shape
+    anchor_index = tuple(range(C // 4, C * 3 // 4))
+    non_anchor_index = tuple(range(0, C // 4)) + tuple(range(C * 3 // 4, C))
+    
+    anchor = x_prime[:, anchor_index, :, :]
+    non_anchor = x_prime[:, non_anchor_index, :, :]
+
+    return anchor, non_anchor
+
+def Multiplexer(anchor, non_anchor):
+    """
+    The inverse opperation of Demultiplexer
+    """
+    _, C, _, _ = non_anchor.shape
+    x_prime = torch.cat((non_anchor[:, : C//2, :, :], anchor, non_anchor[:, C//2:, :, :]), dim=1)
+    return Depth2Space(r=2)(x_prime)
+
+
+if __name__ == '__main__':
+    x = torch.zeros(1, 1, 6, 6)
+    x[0, 0, 0, 0] = 0
+    x[0, 0, 0, 1] = 1
+    x[0, 0, 1, 0] = 2
+    x[0, 0, 1, 1] = 3
+    print(x)
+
+    anchor, non_anchor = Demultiplexer(x)
+    print(anchor)
+    print(non_anchor)
+
+    x = Multiplexer(anchor, non_anchor)
+    print(x)