昇思MindSpore学习笔记6-01LLM原理和实践--FCN图像语义分割

摘要：

        记录MindSpore AI框架使用FCN全卷积网络理解图像进行图像语议分割的过程、步骤和方法。包括环境准备、下载数据集、数据集加载和预处理、构建网络、训练准备、模型训练、模型评估、模型推理等。

一、概念

1.语义分割

图像语义分割

semantic segmentation

        图像处理

        机器视觉

                图像理解

        AI领域重要分支

        应用

                人脸识别

                物体检测

                医学影像

                卫星图像分析

                自动驾驶感知

        目的

                图像每个像素点分类

                输出与输入大小相同的图像

                输出图像的每个像素对应了输入图像每个像素的类别

        图像领域语义

                图像的内容

                对图片意思的理解

实例

2.FCN全卷积网络

Fully Convolutional Networks

图像语义分割框架

        2015年UC Berkeley提出

        端到端(end to end)像素级(pixel level)预测全卷积网络

全卷积神经网络主要使用三种技术：

1.卷积化Convolutional

VGG-16

        FCN的backbone

        输入224*224RGB图像

                固定大小的输入

                丢弃了空间坐标

                产生非空间输出

        输出1000个预测值

卷积层

        输出二维矩阵

        生成输入图片映射的heatmap

2.上采样Upsample

卷积过程

        卷积操作

        池化操作

特征图尺寸变小

上采样操作

        得到原图大小的稠密图像预测

双线性插值参数

初始化上采样逆卷积参数

反向传播学习非线性上采样

3.跳跃结构Skip Layer

将深层的全局信息与浅层的局部信息相结合

                             底层stride 32的预测FCN-32s    2倍上采样

融合（相加）  pool4层stride 16的预测FCN-16s    2倍上采样

融合（相加）  pool3层stride 8的预测FCN-8s

特点:

(1)不含全连接层(fc)的全卷积(fully conv)网络，可适应任意尺寸输入。

(2)增大数据尺寸的反卷积(deconv)层，能够输出精细的结果。

(3)结合不同深度层结果的跳级(skip)结构，同时确保鲁棒性和精确性。

二、环境准备

%%capture captured_output
# 实验环境已经预装了mindspore==2.2.14，如需更换mindspore版本，可更改下面mindspore的版本号
!pip uninstall mindspore -y
!pip install -i https://pypi.mirrors.ustc.edu.cn/simple mindspore==2.2.14
# 查看当前 mindspore 版本
!pip show mindspore

输出：

Name: mindspore
Version: 2.2.14
Summary: MindSpore is a new open source deep learning training/inference framework that could be used for mobile, edge and cloud scenarios.
Home-page: https://www.mindspore.cn
Author: The MindSpore Authors
Author-email: contact@mindspore.cn
License: Apache 2.0
Location: /home/nginx/miniconda/envs/jupyter/lib/python3.9/site-packages
Requires: asttokens, astunparse, numpy, packaging, pillow, protobuf, psutil, scipy
Required-by:

三、数据处理

1.下载数据集

from download import download
​
url = "https://mindspore-website.obs.cn-north-4.myhuaweicloud.com/notebook/datasets/dataset_fcn8s.tar"
​
download(url, "./dataset", kind="tar", replace=True)

输出：

Creating data folder...
Downloading data from https://mindspore-website.obs.cn-north-4.myhuaweicloud.com/notebook/datasets/dataset_fcn8s.tar (537.2 MB)

file_sizes: 100%|█████████████████████████████| 563M/563M [00:03<00:00, 160MB/s]
Extracting tar file...
Successfully downloaded / unzipped to ./dataset
'./dataset'

2.数据预处理

PASCAL VOC 2012数据集图像分辨率不一致

        标准化处理

3.数据加载

混合PASCAL VOC 2012数据集、SDB数据集

import numpy as np
import cv2
import mindspore.dataset as ds
​
class SegDataset:
    def __init__(self,
                 image_mean,
                 image_std,
                 data_file='',
                 batch_size=32,
                 crop_size=512,
                 max_scale=2.0,
                 min_scale=0.5,
                 ignore_label=255,
                 num_classes=21,
                 num_readers=2,
                 num_parallel_calls=4):
​
        self.data_file = data_file
        self.batch_size = batch_size
        self.crop_size = crop_size
        self.image_mean = np.array(image_mean, dtype=np.float32)
        self.image_std = np.array(image_std, dtype=np.float32)
        self.max_scale = max_scale
        self.min_scale = min_scale
        self.ignore_label = ignore_label
        self.num_classes = num_classes
        self.num_readers = num_readers
        self.num_parallel_calls = num_parallel_calls
        max_scale > min_scale
​
    def preprocess_dataset(self, image, label):
        image_out = cv2.imdecode(np.frombuffer(image, dtype=np.uint8), cv2.IMREAD_COLOR)
        label_out = cv2.imdecode(np.frombuffer(label, dtype=np.uint8), cv2.IMREAD_GRAYSCALE)
        sc = np.random.uniform(self.min_scale, self.max_scale)
        new_h, new_w = int(sc * image_out.shape[0]), int(sc * image_out.shape[1])
        image_out = cv2.resize(image_out, (new_w, new_h), interpolation=cv2.INTER_CUBIC)
        label_out = cv2.resize(label_out, (new_w, new_h), interpolation=cv2.INTER_NEAREST)
​
        image_out = (image_out - self.image_mean) / self.image_std
        out_h, out_w = max(new_h, self.crop_size), max(new_w, self.crop_size)
        pad_h, pad_w = out_h - new_h, out_w - new_w
        if pad_h > 0 or pad_w > 0:
            image_out = cv2.copyMakeBorder(image_out, 0, pad_h, 0, pad_w, cv2.BORDER_CONSTANT, value=0)
            label_out = cv2.copyMakeBorder(label_out, 0, pad_h, 0, pad_w, cv2.BORDER_CONSTANT, value=self.ignore_label)
        offset_h = np.random.randint(0, out_h - self.crop_size + 1)
        offset_w = np.random.randint(0, out_w - self.crop_size + 1)
        image_out = image_out[offset_h: offset_h + self.crop_size, offset_w: offset_w + self.crop_size, :]
        label_out = label_out[offset_h: offset_h + self.crop_size, offset_w: offset_w+self.crop_size]
        if np.random.uniform(0.0, 1.0) > 0.5:
            image_out = image_out[:, ::-1, :]
            label_out = label_out[:, ::-1]
        image_out = image_out.transpose((2, 0, 1))
        image_out = image_out.copy()
        label_out = label_out.copy()
        label_out = label_out.astype("int32")
        return image_out, label_out
​
    def get_dataset(self):
        ds.config.set_numa_enable(True)
        dataset = ds.MindDataset(self.data_file, columns_list=["data", "label"],
                                 shuffle=True, num_parallel_workers=self.num_readers)
        transforms_list = self.preprocess_dataset
        dataset = dataset.map(operations=transforms_list, input_columns=["data", "label"],
                              output_columns=["data", "label"],
                              num_parallel_workers=self.num_parallel_calls)
        dataset = dataset.shuffle(buffer_size=self.batch_size * 10)
        dataset = dataset.batch(self.batch_size, drop_remainder=True)
        return dataset
​
​
# 定义创建数据集的参数
IMAGE_MEAN = [103.53, 116.28, 123.675]
IMAGE_STD = [57.375, 57.120, 58.395]
DATA_FILE = "dataset/dataset_fcn8s/mindname.mindrecord"
​
# 定义模型训练参数
train_batch_size = 4
crop_size = 512
min_scale = 0.5
max_scale = 2.0
ignore_label = 255
num_classes = 21
​
# 实例化Dataset
dataset = SegDataset(image_mean=IMAGE_MEAN,
                     image_std=IMAGE_STD,
                     data_file=DATA_FILE,
                     batch_size=train_batch_size,
                     crop_size=crop_size,
                     max_scale=max_scale,
                     min_scale=min_scale,
                     ignore_label=ignore_label,
                     num_classes=num_classes,
                     num_readers=2,
                     num_parallel_calls=4)
​
dataset = dataset.get_dataset()

4.训练集可视化

import numpy as np
import matplotlib.pyplot as plt
​
plt.figure(figsize=(16, 8))
​
# 对训练集中的数据进行展示
for i in range(1, 9):
    plt.subplot(2, 4, i)
    show_data = next(dataset.create_dict_iterator())
    show_images = show_data["data"].asnumpy()
    show_images = np.clip(show_images, 0, 1)
# 将图片转换HWC格式后进行展示
    plt.imshow(show_images[0].transpose(1, 2, 0))
    plt.axis("off")
    plt.subplots_adjust(wspace=0.05, hspace=0)
plt.show()

输出：

四、网络构建

FCN网络流程

        输入图像image

        pool1池化

                尺寸变为原始尺寸的1/2

        pool2池化

                尺寸变为原始尺寸的1/4

        pool3池化

                尺寸变为原始尺寸的1/8

        pool4池化

                尺寸变为原始尺寸的1/16

        pool5池化

                尺寸变为原始尺寸的1/32

        conv6-7卷积

                输出尺寸原图的1/32

        FCN-32s

                反卷积扩大到原始尺寸

        FCN-16s

                融合

                        conv7反卷积尺寸扩大两倍至原图的1/16

                        pool4特征图

                反卷积扩大到原始尺寸

        FCN-8s

                融合

                        conv7反卷积尺寸扩大4倍

                        pool4特征图反卷积扩大2倍

                        pool3特征图

                反卷积扩大到原始尺寸

构建FCN-8s网络代码：

import mindspore.nn as nn
​
class FCN8s(nn.Cell):
    def __init__(self, n_class):
        super().__init__()
        self.n_class = n_class
        self.conv1 = nn.SequentialCell(
            nn.Conv2d(in_channels=3, out_channels=64,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(64),
            nn.ReLU(),
            nn.Conv2d(in_channels=64, out_channels=64,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(64),
            nn.ReLU()
        )
        self.pool1 = nn.MaxPool2d(kernel_size=2, stride=2)
        self.conv2 = nn.SequentialCell(
            nn.Conv2d(in_channels=64, out_channels=128,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(128),
            nn.ReLU(),
            nn.Conv2d(in_channels=128, out_channels=128,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(128),
            nn.ReLU()
        )
        self.pool2 = nn.MaxPool2d(kernel_size=2, stride=2)
        self.conv3 = nn.SequentialCell(
            nn.Conv2d(in_channels=128, out_channels=256,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(256),
            nn.ReLU(),
            nn.Conv2d(in_channels=256, out_channels=256,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(256),
            nn.ReLU(),
            nn.Conv2d(in_channels=256, out_channels=256,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(256),
            nn.ReLU()
        )
        self.pool3 = nn.MaxPool2d(kernel_size=2, stride=2)
        self.conv4 = nn.SequentialCell(
            nn.Conv2d(in_channels=256, out_channels=512,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(512),
            nn.ReLU(),
            nn.Conv2d(in_channels=512, out_channels=512,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(512),
            nn.ReLU(),
            nn.Conv2d(in_channels=512, out_channels=512,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(512),
            nn.ReLU()
        )
        self.pool4 = nn.MaxPool2d(kernel_size=2, stride=2)
        self.conv5 = nn.SequentialCell(
            nn.Conv2d(in_channels=512, out_channels=512,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(512),
            nn.ReLU(),
            nn.Conv2d(in_channels=512, out_channels=512,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(512),
            nn.ReLU(),
            nn.Conv2d(in_channels=512, out_channels=512,
                      kernel_size=3, weight_init='xavier_uniform'),
            nn.BatchNorm2d(512),
            nn.ReLU()
        )
        self.pool5 = nn.MaxPool2d(kernel_size=2, stride=2)
        self.conv6 = nn.SequentialCell(
            nn.Conv2d(in_channels=512, out_channels=4096,
                      kernel_size=7, weight_init='xavier_uniform'),
            nn.BatchNorm2d(4096),
            nn.ReLU(),
        )
        self.conv7 = nn.SequentialCell(
            nn.Conv2d(in_channels=4096, out_channels=4096,
                      kernel_size=1, weight_init='xavier_uniform'),
            nn.BatchNorm2d(4096),
            nn.ReLU(),
        )
        self.score_fr = nn.Conv2d(in_channels=4096, out_channels=self.n_class,
                                  kernel_size=1, weight_init='xavier_uniform')
        self.upscore2 = nn.Conv2dTranspose(in_channels=self.n_class, out_channels=self.n_class,
                                           kernel_size=4, stride=2, weight_init='xavier_uniform')
        self.score_pool4 = nn.Conv2d(in_channels=512, out_channels=self.n_class,
                                     kernel_size=1, weight_init='xavier_uniform')
        self.upscore_pool4 = nn.Conv2dTranspose(in_channels=self.n_class, out_channels=self.n_class,
                                                kernel_size=4, stride=2, weight_init='xavier_uniform')
        self.score_pool3 = nn.Conv2d(in_channels=256, out_channels=self.n_class,
                                     kernel_size=1, weight_init='xavier_uniform')
        self.upscore8 = nn.Conv2dTranspose(in_channels=self.n_class, out_channels=self.n_class,
                                           kernel_size=16, stride=8, weight_init='xavier_uniform')
​
    def construct(self, x):
        x1 = self.conv1(x)
        p1 = self.pool1(x1)
        x2 = self.conv2(p1)
        p2 = self.pool2(x2)
        x3 = self.conv3(p2)
        p3 = self.pool3(x3)
        x4 = self.conv4(p3)
        p4 = self.pool4(x4)
        x5 = self.conv5(p4)
        p5 = self.pool5(x5)
        x6 = self.conv6(p5)
        x7 = self.conv7(x6)
        sf = self.score_fr(x7)
        u2 = self.upscore2(sf)
        s4 = self.score_pool4(p4)
        f4 = s4 + u2
        u4 = self.upscore_pool4(f4)
        s3 = self.score_pool3(p3)
        f3 = s3 + u4
        out = self.upscore8(f3)
        return out

五、训练准备

1.导入VGG-16部分预训练权重

from download import download
from mindspore import load_checkpoint, load_param_into_net
​
url = "https://mindspore-website.obs.cn-north-4.myhuaweicloud.com/notebook/datasets/fcn8s_vgg16_pretrain.ckpt"
download(url, "fcn8s_vgg16_pretrain.ckpt", replace=True)
def load_vgg16():
    ckpt_vgg16 = "fcn8s_vgg16_pretrain.ckpt"
    param_vgg = load_checkpoint(ckpt_vgg16)
    load_param_into_net(net, param_vgg)

输出：

Downloading data from https://mindspore-website.obs.cn-north-4.myhuaweicloud.com/notebook/datasets/fcn8s_vgg16_pretrain.ckpt (513.2 MB)

file_sizes: 100%|█████████████████████████████| 538M/538M [00:03<00:00, 179MB/s]
Successfully downloaded file to fcn8s_vgg16_pretrain.ckpt

2.损失函数

交叉熵损失函数

mindspore.nn.CrossEntropyLoss()

计算FCN网络输出与mask之间的交叉熵损失

3.自定义评价指标 Metrics

用于评估模型效果

设共有 K+1个类

        从L_0 到L_{ki}

        其中包含一个空类或背景

P_{ij}表示本属于i类但被预测为j类的像素数量

P_{ii}表示真正的数量

P_{ij}P_{ji}则分别被解释为假正和假负

Pixel Accuracy

PA像素精度

        标记正确的像素占总像素的比例。

PA=\frac{\sum_{i=0}^{k}P_{ii}}{\sum_{i=0}^{k}\sum_{j=0}^{k}P_{ij}}

Mean Pixel Accuracy

MPA均像素精度

计算每个类内正确分类像素数的比例

求所有类的平均

MPA=\frac{1}{K+1}\sum \sum_{i=0}^{k}\frac{P_{ii}}{\sum_{j=0}^{k}P_{ij}}

Mean Intersection over Union

MloU均交并比

        语义分割的标准度量

                计算两个集合的交集和并集之比

                        交集为真实值（ground truth)

                        并集为预测值（predicted segmentation）

                两者之比：正真数 (intersection) /（真正+假负+假正（并集））

                在每个类上计算loU

                平均

MIoU=\frac{1}{K+1} \sum_{i=0}^{k}\frac{p_{ii}}{\sum_{j=0}^{k}p_{ij}+{\sum_{j=0}^{k}p_{ji}}-p_{ii}}

Frequency Weighted Intersection over Union

FWIoU频权交井比

根据每个类出现的频率设置权重

FWIoU=\frac{1}{\sum_{i=0}^{k}\sum_{j=0}^{k}p_{ij}} \sum_{i=0}^{k}\frac{p_{ii}}{\sum_{j=0}^{k}p_{ij}+{\sum_{j=0}^{k}p_{ji}}-p_{ii}}

import numpy as np
import mindspore as ms
import mindspore.nn as nn
import mindspore.train as train
​
class PixelAccuracy(train.Metric):
    def __init__(self, num_class=21):
        super(PixelAccuracy, self).__init__()
        self.num_class = num_class
​
    def _generate_matrix(self, gt_image, pre_image):
        mask = (gt_image >= 0) & (gt_image < self.num_class)
        label = self.num_class * gt_image[mask].astype('int') + pre_image[mask]
        count = np.bincount(label, minlength=self.num_class**2)
        confusion_matrix = count.reshape(self.num_class, self.num_class)
        return confusion_matrix
​
    def clear(self):
        self.confusion_matrix = np.zeros((self.num_class,) * 2)
​
    def update(self, *inputs):
        y_pred = inputs[0].asnumpy().argmax(axis=1)
        y = inputs[1].asnumpy().reshape(4, 512, 512)
        self.confusion_matrix += self._generate_matrix(y, y_pred)
​
    def eval(self):
        pixel_accuracy = np.diag(self.confusion_matrix).sum() / self.confusion_matrix.sum()
        return pixel_accuracy
​
​
class PixelAccuracyClass(train.Metric):
    def __init__(self, num_class=21):
        super(PixelAccuracyClass, self).__init__()
        self.num_class = num_class
​
    def _generate_matrix(self, gt_image, pre_image):
        mask = (gt_image >= 0) & (gt_image < self.num_class)
        label = self.num_class * gt_image[mask].astype('int') + pre_image[mask]
        count = np.bincount(label, minlength=self.num_class**2)
        confusion_matrix = count.reshape(self.num_class, self.num_class)
        return confusion_matrix
​
    def update(self, *inputs):
        y_pred = inputs[0].asnumpy().argmax(axis=1)
        y = inputs[1].asnumpy().reshape(4, 512, 512)
        self.confusion_matrix += self._generate_matrix(y, y_pred)
​
    def clear(self):
        self.confusion_matrix = np.zeros((self.num_class,) * 2)
​
    def eval(self):
        mean_pixel_accuracy = np.diag(self.confusion_matrix) / self.confusion_matrix.sum(axis=1)
        mean_pixel_accuracy = np.nanmean(mean_pixel_accuracy)
        return mean_pixel_accuracy
​
​
class MeanIntersectionOverUnion(train.Metric):
    def __init__(self, num_class=21):
        super(MeanIntersectionOverUnion, self).__init__()
        self.num_class = num_class
​
    def _generate_matrix(self, gt_image, pre_image):
        mask = (gt_image >= 0) & (gt_image < self.num_class)
        label = self.num_class * gt_image[mask].astype('int') + pre_image[mask]
        count = np.bincount(label, minlength=self.num_class**2)
        confusion_matrix = count.reshape(self.num_class, self.num_class)
        return confusion_matrix
​
    def update(self, *inputs):
        y_pred = inputs[0].asnumpy().argmax(axis=1)
        y = inputs[1].asnumpy().reshape(4, 512, 512)
        self.confusion_matrix += self._generate_matrix(y, y_pred)
​
    def clear(self):
        self.confusion_matrix = np.zeros((self.num_class,) * 2)
​
    def eval(self):
        mean_iou = np.diag(self.confusion_matrix) / (
            np.sum(self.confusion_matrix, axis=1) + np.sum(self.confusion_matrix, axis=0) -
            np.diag(self.confusion_matrix))
        mean_iou = np.nanmean(mean_iou)
        return mean_iou
​
​
class FrequencyWeightedIntersectionOverUnion(train.Metric):
    def __init__(self, num_class=21):
        super(FrequencyWeightedIntersectionOverUnion, self).__init__()
        self.num_class = num_class
​
    def _generate_matrix(self, gt_image, pre_image):
        mask = (gt_image >= 0) & (gt_image < self.num_class)
        label = self.num_class * gt_image[mask].astype('int') + pre_image[mask]
        count = np.bincount(label, minlength=self.num_class**2)
        confusion_matrix = count.reshape(self.num_class, self.num_class)
        return confusion_matrix
​
    def update(self, *inputs):
        y_pred = inputs[0].asnumpy().argmax(axis=1)
        y = inputs[1].asnumpy().reshape(4, 512, 512)
        self.confusion_matrix += self._generate_matrix(y, y_pred)
​
    def clear(self):
        self.confusion_matrix = np.zeros((self.num_class,) * 2)
​
    def eval(self):
        freq = np.sum(self.confusion_matrix, axis=1) / np.sum(self.confusion_matrix)
        iu = np.diag(self.confusion_matrix) / (
            np.sum(self.confusion_matrix, axis=1) + np.sum(self.confusion_matrix, axis=0) -
            np.diag(self.confusion_matrix))
​
        frequency_weighted_iou = (freq[freq > 0] * iu[freq > 0]).sum()
        return frequency_weighted_iou

六、模型训练

导入VGG-16预训练参数

实例化损失函数、优化器

Model接口编译网络

训练FCN-8s网络

import mindspore
from mindspore import Tensor
import mindspore.nn as nn
from mindspore.train import ModelCheckpoint, CheckpointConfig, LossMonitor, TimeMonitor, Model
​
device_target = "Ascend"
mindspore.set_context(mode=mindspore.PYNATIVE_MODE, device_target=device_target)
​
train_batch_size = 4
num_classes = 21
# 初始化模型结构
net = FCN8s(n_class=21)
# 导入vgg16预训练参数
load_vgg16()
# 计算学习率
min_lr = 0.0005
base_lr = 0.05
train_epochs = 1
iters_per_epoch = dataset.get_dataset_size()
total_step = iters_per_epoch * train_epochs
​
lr_scheduler = mindspore.nn.cosine_decay_lr(min_lr,
                                            base_lr,
                                            total_step,
                                            iters_per_epoch,
                                            decay_epoch=2)
lr = Tensor(lr_scheduler[-1])
​
# 定义损失函数
loss = nn.CrossEntropyLoss(ignore_index=255)
# 定义优化器
optimizer = nn.Momentum(params=net.trainable_params(), learning_rate=lr, momentum=0.9, weight_decay=0.0001)
# 定义loss_scale
scale_factor = 4
scale_window = 3000
loss_scale_manager = ms.amp.DynamicLossScaleManager(scale_factor, scale_window)
# 初始化模型
if device_target == "Ascend":
    model = Model(net, loss_fn=loss, optimizer=optimizer, loss_scale_manager=loss_scale_manager, metrics={"pixel accuracy": PixelAccuracy(), "mean pixel accuracy": PixelAccuracyClass(), "mean IoU": MeanIntersectionOverUnion(), "frequency weighted IoU": FrequencyWeightedIntersectionOverUnion()})
else:
    model = Model(net, loss_fn=loss, optimizer=optimizer, metrics={"pixel accuracy": PixelAccuracy(), "mean pixel accuracy": PixelAccuracyClass(), "mean IoU": MeanIntersectionOverUnion(), "frequency weighted IoU": FrequencyWeightedIntersectionOverUnion()})
​
# 设置ckpt文件保存的参数
time_callback = TimeMonitor(data_size=iters_per_epoch)
loss_callback = LossMonitor()
callbacks = [time_callback, loss_callback]
save_steps = 330
keep_checkpoint_max = 5
config_ckpt = CheckpointConfig(save_checkpoint_steps=10,
                               keep_checkpoint_max=keep_checkpoint_max)
ckpt_callback = ModelCheckpoint(prefix="FCN8s",
                                directory="./ckpt",
                                config=config_ckpt)
callbacks.append(ckpt_callback)
model.train(train_epochs, dataset, callbacks=callbacks)

输出：

epoch: 1 step: 1, loss is 3.0504844
epoch: 1 step: 2, loss is 3.017057
epoch: 1 step: 3, loss is 2.9523003
epoch: 1 step: 4, loss is 2.9488814
epoch: 1 step: 5, loss is 2.666231
epoch: 1 step: 6, loss is 2.7145326
epoch: 1 step: 7, loss is 1.796408
epoch: 1 step: 8, loss is 1.5167583
epoch: 1 step: 9, loss is 1.6862022
epoch: 1 step: 10, loss is 2.4622822
......
epoch: 1 step: 1141, loss is 1.70966
epoch: 1 step: 1142, loss is 1.434751
epoch: 1 step: 1143, loss is 2.406475
Train epoch time: 762889.258 ms, per step time: 667.445 ms

七、模型评估

IMAGE_MEAN = [103.53, 116.28, 123.675]
IMAGE_STD = [57.375, 57.120, 58.395]
DATA_FILE = "dataset/dataset_fcn8s/mindname.mindrecord"
​
# 下载已训练好的权重文件
url = "https://mindspore-website.obs.cn-north-4.myhuaweicloud.com/notebook/datasets/FCN8s.ckpt"
download(url, "FCN8s.ckpt", replace=True)
net = FCN8s(n_class=num_classes)
​
ckpt_file = "FCN8s.ckpt"
param_dict = load_checkpoint(ckpt_file)
load_param_into_net(net, param_dict)
​
if device_target == "Ascend":
    model = Model(net, loss_fn=loss, optimizer=optimizer, loss_scale_manager=loss_scale_manager, metrics={"pixel accuracy": PixelAccuracy(), "mean pixel accuracy": PixelAccuracyClass(), "mean IoU": MeanIntersectionOverUnion(), "frequency weighted IoU": FrequencyWeightedIntersectionOverUnion()})
else:
    model = Model(net, loss_fn=loss, optimizer=optimizer, metrics={"pixel accuracy": PixelAccuracy(), "mean pixel accuracy": PixelAccuracyClass(), "mean IoU": MeanIntersectionOverUnion(), "frequency weighted IoU": FrequencyWeightedIntersectionOverUnion()})
​
# 实例化Dataset
dataset = SegDataset(image_mean=IMAGE_MEAN,
                     image_std=IMAGE_STD,
                     data_file=DATA_FILE,
                     batch_size=train_batch_size,
                     crop_size=crop_size,
                     max_scale=max_scale,
                     min_scale=min_scale,
                     ignore_label=ignore_label,
                     num_classes=num_classes,
                     num_readers=2,
                     num_parallel_calls=4)
dataset_eval = dataset.get_dataset()
model.eval(dataset_eval)

输出：

Downloading data from https://mindspore-website.obs.cn-north-4.myhuaweicloud.com/notebook/datasets/FCN8s.ckpt (1.00 GB)

file_sizes: 100%|██████████████████████████| 1.08G/1.08G [00:10<00:00, 99.7MB/s]
Successfully downloaded file to FCN8s.ckpt
/
{'pixel accuracy': 0.9734831394168291,
 'mean pixel accuracy': 0.9423324801371116,
 'mean IoU': 0.8961453779807752,
 'frequency weighted IoU': 0.9488883312345654}

八、模型推理

使用训练的网络对模型推理结果进行展示。

import cv2
import matplotlib.pyplot as plt
​
net = FCN8s(n_class=num_classes)
# 设置超参
ckpt_file = "FCN8s.ckpt"
param_dict = load_checkpoint(ckpt_file)
load_param_into_net(net, param_dict)
eval_batch_size = 4
img_lst = []
mask_lst = []
res_lst = []
# 推理效果展示(上方为输入图片，下方为推理效果图片)
plt.figure(figsize=(8, 5))
show_data = next(dataset_eval.create_dict_iterator())
show_images = show_data["data"].asnumpy()
mask_images = show_data["label"].reshape([4, 512, 512])
show_images = np.clip(show_images, 0, 1)
for i in range(eval_batch_size):
    img_lst.append(show_images[i])
    mask_lst.append(mask_images[i])
res = net(show_data["data"]).asnumpy().argmax(axis=1)
for i in range(eval_batch_size):
    plt.subplot(2, 4, i + 1)
    plt.imshow(img_lst[i].transpose(1, 2, 0))
    plt.axis("off")
    plt.subplots_adjust(wspace=0.05, hspace=0.02)
    plt.subplot(2, 4, i + 5)
    plt.imshow(res[i])
    plt.axis("off")
    plt.subplots_adjust(wspace=0.05, hspace=0.02)
plt.show()

输出：

九、总结

FCN

        使用全卷积层

        通过学习让图片实现端到端分割。

        优点：

                输入接受任意大小的图像

                高效，避免了由于使用像素块而带来的重复存储和计算卷积的问题。

        待改进之处：

                结果不够精细。比较模糊和平滑，边界处细节不敏感。

                像素分类，没有考虑像素之间的关系（如不连续性和相似性）

                忽略空间规整（spatial regularization）步骤，缺乏空间一致性。

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