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目录

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实验1：K近邻算法实现红酒聚类

数据准备

模型构建--计算距离

计算演示

模型预测

实验2：基于MobileNetv2的垃圾分类

任务说明

数据集

参数配置（训练/验证/推理）

数据预处理

MobileNetV2模型搭建

MobileNetV2模型的训练与测试

模型训练与测试

训练过程

模型推理

导出AIR/GEIR/ONNX模型文件

---

此次两个分类实验中，一个是经典的knn聚类算法，一种是轻量级cnn网络，都是基于较轻资源可以实现的任务。

可以在任务简单、逻辑清晰的任务中使用。

实验1：K近邻算法实现红酒聚类

K近邻算法（K-Nearest-Neighbor, KNN）是一种用于分类和回归的非参数统计方法，于1968年提出(Cover等人,1967)。

• 思想：如何确定某个样本的类别？计算 & 找出该样本与所有样本的中距离最近的K个样本；统计这K个样本的类别并投票，投票最多的类别即确定为该样本的类别。
• knn的3个要素：

1. K值，一个样本的分类是由K个邻居的“多数表决”确定的。K值越小，容易受噪声影响，反之，会使类别之间的界限变得模糊。k的取值可以根据问题和数据特点来确定。在具体实现时，可以考虑样本的权重，即每个样本有不同的投票权重，这种方法称为带权重的k近邻算法，它是一种变种的k近邻算法。如，带样本权重的回归预测函数为：，其中𝑤𝑖 为第个 𝑖 样本的权重。

2. 距离度量，反映了特征空间中两个样本间的相似度，距离越小，越相似。常用的有Lp距离（p=2时，即为欧式距离）、曼哈顿距离、海明距离、切比雪夫距离等。

3. 分类决策规则，通常是多数表决，或者基于距离加权的多数表决（权值与距离成反比）。

数据准备

Wine数据集是模式识别最著名的数据集之一，Wine数据集的官网：Wine Data Set。这些数据是对来自意大利同一地区但来自三个不同品种的葡萄酒进行化学分析的结果。数据集分析了三种葡萄酒中每种所含13种成分的量。这些13种属性是

1. Alcohol，酒精
2. Malic acid，苹果酸
3. Ash，灰
4. Alcalinity of ash，灰的碱度
5. Magnesium，镁
6. Total phenols，总酚
7. Flavanoids，类黄酮
8. Nonflavanoid phenols，非黄酮酚
9. Proanthocyanins，原花青素
10. Color intensity，色彩强度
11. Hue，色调
12. OD280/OD315 of diluted wines，稀释酒的OD280/OD315
13. Proline，脯氨酸

• 方式一，从Wine数据集官网下载wine.data文件。
• 方式二，从华为云OBS中下载wine.data文件。

部分数据如下图：第1列为类别，2～14列为13种化学成分数据。

共178条数据，其中1类是1-59，行，2类是60-130行，3类是131-178行。取两个属性观察样本分布情况和可区分性，如下图。

共178条数据，按照128:50划分为训练集和验证集样本。

import numpy as np

train_idx = np.random.choice(178, 128, replace=False)
test_idx = np.array(list(set(range(178)) - set(train_idx)))
X_train, Y_train = X[train_idx], Y[train_idx]
X_test, Y_test = X[test_idx], Y[test_idx]

print(np.shape(X_train))   ### (128, 13)
print(np.shape(X_test))    ### (50, 13)
print(np.shape(Y_train))   ## (128,)
print(np.shape(Y_test))

模型构建--计算距离

同样地，继承 nn.Cell 类构建模型，使用 ops.tile, square, ReduceSum, sqrt, TopK等算子，通过矩阵运算的方式同时计算输入样本x和已明确分类的其他样本X_train的距离（欧式距离），并计算出top k 近邻。

class KnnNet(nn.Cell):
    def __init__(self, k):
        super(KnnNet, self).__init__()
        self.k = k

    def construct(self, x, X_train):
        #平铺输入x以匹配X_train中的样本数，即复制x到128份与X_train一样的维度，方便计算。
        x_tile = ops.tile(x, (128, 1))
        square_diff = ops.square(x_tile - X_train)
        square_dist = ops.sum(square_diff, 1)
        dist = ops.sqrt(square_dist)
        #-dist表示值越大，样本就越接近: 沿给定维度查找k个最大或最小元素和对应的索引，需要排序的维度dims=None,因为是1维。默认 sorted=True 按值降序排序。
        ### 负最大，即正距离最小即最近邻的K个值
        values, indices = ops.topk(-dist, self.k)
        return indices

def knn(knn_net, x, X_train, Y_train):
    x, X_train = ms.Tensor(x), ms.Tensor(X_train)
    indices = knn_net(x, X_train)
    topk_cls = [0]*len(indices.asnumpy())
    for idx in indices.asnumpy():
        topk_cls[Y_train[idx]] += 1
    cls = np.argmax(topk_cls)
    return cls

计算演示

如上图，是针对一个验证样本，筛选出来13个特征中计算knn 算法的5个距离最小的样本后，拿到对应的分类类别 Y_train[idx]，为k=5个样本对应的类别进行统计，取统计值最大的类别np.argmax(topk_cls)即为分类结果。

模型预测

下面是所有验证样本的统计，计算验证精度。

acc = 0
knn_net = KnnNet(5)
for x, y in zip(X_test, Y_test):
    pred = knn(knn_net, x, X_train, Y_train)
    acc += (pred == y)
    print('label: %d, prediction: %s' % (y, pred))

print('Validation accuracy is %f' % (acc/len(Y_test)))

根据下图演示，说明KNN算法在该3分类任务上有效，能根据酒的13种属性判断出酒的品种。多次改变k测试，效果一般，验证精度不超过80%。

实验2：基于MobileNetv2的垃圾分类

MobileNet网络是由Google团队于2017年提出的专注于移动端、嵌入式或IoT设备的轻量级CNN网络，相比于传统的卷积神经网络，MobileNet网络使用深度可分离卷积（Depthwise Separable Convolution）的思想在准确率小幅度降低的前提下，大大减小了模型参数与运算量。并引入宽度系数 α和分辨率系数 β使模型满足不同应用场景的需求。

由于MobileNet网络中Relu激活函数处理低维特征信息时会存在大量的丢失，所以MobileNetV2网络提出使用倒残差结构（Inverted residual block）和 Linear Bottlenecks来设计网络，以提高模型的准确率，且优化后的模型更小。

如下图，Inverted residual block结构是先使用1x1卷积进行升维，然后使用3x3的DepthWise卷积，最后使用1x1的卷积进行降维，与Residual block结构相反。Residual block是先使用1x1的卷积进行降维，然后使用3x3的卷积，最后使用1x1的卷积进行升维。

• 说明： 详细内容可参见MobileNetV2论文

任务说明

通过读取本地图像数据作为输入，对图像中的垃圾物体进行检测，并且将检测结果图片保存到文件中。

数据集

• 权重文件：
• https://ascend-professional-construction-dataset.obs.cn-north-4.myhuaweicloud.com:443/ComputerVision/mobilenetV2-200_1067.zip
• 数据文件：
• https://ascend-professional-construction-dataset.obs.cn-north-4.myhuaweicloud.com:443/MindStudio-pc/data_en.zip
• 环境添加：`pip install easydict`

import math
import numpy as np
import os
import random
from download import download

from matplotlib import pyplot as plt
from easydict import EasyDict
from PIL import Image
import numpy as np
import mindspore.nn as nn
from mindspore import ops as P
from mindspore.ops import add
from mindspore import Tensor
import mindspore.common.dtype as mstype
import mindspore.dataset as de
import mindspore.dataset.vision as C
import mindspore.dataset.transforms as C2
import mindspore as ms
from mindspore import set_context, nn, Tensor, load_checkpoint, save_checkpoint, export
from mindspore.train import Model
from mindspore.train import Callback, LossMonitor, ModelCheckpoint, CheckpointConfig

os.environ['GLOG_v'] = '3' # Log level includes 3(ERROR), 2(WARNING), 1(INFO), 0(DEBUG).
os.environ['GLOG_logtostderr'] = '0' # 0：输出到文件，1：输出到屏幕
os.environ['GLOG_log_dir'] = '../../log' # 日志目录
os.environ['GLOG_stderrthreshold'] = '2' # 输出到目录也输出到屏幕：3(ERROR), 2(WARNING), 1(INFO), 0(DEBUG).
set_context(mode=ms.GRAPH_MODE, device_target="CPU", device_id=0) # 设置采用图模式执行，设备为Ascend#


# 下载预训练权重文件
url = "https://ascend-professional-construction-dataset.obs.cn-north-4.myhuaweicloud.com:443/ComputerVision/mobilenetV2-200_1067.zip" 
path = download(url, "./", kind="zip", replace=True)

https://ascend-professional-construction-dataset.obs.cn-north-4.myhuaweicloud.com:443/MindStudio-pc/data_en.zip

参数配置（训练/验证/推理）

# 垃圾分类数据集标签，以及用于标签映射的字典。
garbage_classes = {
    '干垃圾': ['贝壳', '打火机', '旧镜子', '扫把', '陶瓷碗', '牙刷', '一次性筷子', '脏污衣服'],
    '可回收物': ['报纸', '玻璃制品', '篮球', '塑料瓶', '硬纸板', '玻璃瓶', '金属制品', '帽子', '易拉罐', '纸张'],
    '湿垃圾': ['菜叶', '橙皮', '蛋壳', '香蕉皮'],
    '有害垃圾': ['电池', '药片胶囊', '荧光灯', '油漆桶']
}

class_cn = ['贝壳', '打火机', '旧镜子', '扫把', '陶瓷碗', '牙刷', '一次性筷子', '脏污衣服',
            '报纸', '玻璃制品', '篮球', '塑料瓶', '硬纸板', '玻璃瓶', '金属制品', '帽子', '易拉罐', '纸张',
            '菜叶', '橙皮', '蛋壳', '香蕉皮',
            '电池', '药片胶囊', '荧光灯', '油漆桶']
class_en = ['Seashell', 'Lighter','Old Mirror', 'Broom','Ceramic Bowl', 'Toothbrush','Disposable Chopsticks','Dirty Cloth',
            'Newspaper', 'Glassware', 'Basketball', 'Plastic Bottle', 'Cardboard','Glass Bottle', 'Metalware', 'Hats', 'Cans', 'Paper',
            'Vegetable Leaf','Orange Peel', 'Eggshell','Banana Peel',
            'Battery', 'Tablet capsules','Fluorescent lamp', 'Paint bucket']

index_en = {'Seashell': 0, 'Lighter': 1, 'Old Mirror': 2, 'Broom': 3, 'Ceramic Bowl': 4, 'Toothbrush': 5, 'Disposable Chopsticks': 6, 'Dirty Cloth': 7,
            'Newspaper': 8, 'Glassware': 9, 'Basketball': 10, 'Plastic Bottle': 11, 'Cardboard': 12, 'Glass Bottle': 13, 'Metalware': 14, 'Hats': 15, 'Cans': 16, 'Paper': 17,
            'Vegetable Leaf': 18, 'Orange Peel': 19, 'Eggshell': 20, 'Banana Peel': 21,
            'Battery': 22, 'Tablet capsules': 23, 'Fluorescent lamp': 24, 'Paint bucket': 25}

# 训练超参
config = EasyDict({
    "num_classes": 26,
    "image_height": 224,
    "image_width": 224,
    #"data_split": [0.9, 0.1],
    "backbone_out_channels":1280,
    "batch_size": 16,
    "eval_batch_size": 8,
    "epochs": 10,
    "lr_max": 0.05,
    "momentum": 0.9,
    "weight_decay": 1e-4,
    "save_ckpt_epochs": 1,
    "dataset_path": "./data_en",
    "class_index": index_en,
    "pretrained_ckpt": "./mobilenetV2-200_1067.ckpt" # mobilenetV2-200_1067.ckpt 
})

数据预处理

用ImageFolderDataset方法读取垃圾分类数据集，并整体对数据集进行处理。

读取数据集时指定训练集和测试集，首先对整个数据集进行归一化，修改图像频道等预处理操作。然后对训练集的数据依次进行RandomCropDecodeResize、RandomHorizontalFlip、RandomColorAdjust、shuffle操作，以增加训练数据的丰富度；对测试集进行Decode、Resize、CenterCrop等预处理操作；最后返回处理后的数据集。

def create_dataset(dataset_path, config, training=True, buffer_size=1000):
    """
    create a train or eval dataset

    Args:
        dataset_path(string): the path of dataset.
        config(struct): the config of train and eval in diffirent platform.

    Returns:
        train_dataset, val_dataset
    """
    data_path = os.path.join(dataset_path, 'train' if training else 'test')
    ds = de.ImageFolderDataset(data_path, num_parallel_workers=4, class_indexing=config.class_index)
    resize_height = config.image_height
    resize_width = config.image_width
    
    normalize_op = C.Normalize(mean=[0.485*255, 0.456*255, 0.406*255], std=[0.229*255, 0.224*255, 0.225*255])
    change_swap_op = C.HWC2CHW()
    type_cast_op = C2.TypeCast(mstype.int32)

    if training:
        crop_decode_resize = C.RandomCropDecodeResize(resize_height, scale=(0.08, 1.0), ratio=(0.75, 1.333))
        horizontal_flip_op = C.RandomHorizontalFlip(prob=0.5)
        color_adjust = C.RandomColorAdjust(brightness=0.4, contrast=0.4, saturation=0.4)
    
        train_trans = [crop_decode_resize, horizontal_flip_op, color_adjust, normalize_op, change_swap_op]
        train_ds = ds.map(input_columns="image", operations=train_trans, num_parallel_workers=4)
        train_ds = train_ds.map(input_columns="label", operations=type_cast_op, num_parallel_workers=4)
        
        train_ds = train_ds.shuffle(buffer_size=buffer_size)
        ds = train_ds.batch(config.batch_size, drop_remainder=True)
    else:
        decode_op = C.Decode()
        resize_op = C.Resize((int(resize_width/0.875), int(resize_width/0.875)))
        center_crop = C.CenterCrop(resize_width)
        
        eval_trans = [decode_op, resize_op, center_crop, normalize_op, change_swap_op]
        eval_ds = ds.map(input_columns="image", operations=eval_trans, num_parallel_workers=4)
        eval_ds = eval_ds.map(input_columns="label", operations=type_cast_op, num_parallel_workers=4)
        ds = eval_ds.batch(config.eval_batch_size, drop_remainder=True)

    return ds



ds = create_dataset(dataset_path=config.dataset_path, config=config, training=False)
print(ds.get_dataset_size())
data = ds.create_dict_iterator(output_numpy=True)._get_next()
images = data['image']
labels = data['label']

for i in range(1, 5):
    plt.subplot(2, 2, i)
    plt.imshow(np.transpose(images[i], (1,2,0)))
    plt.title('label: %s' % class_en[labels[i]])
    plt.xticks([])
plt.show()

处理后的数据展示

MobileNetV2模型搭建

继承mindspore.nn.Cell基类搭建网络。

1）各层需要预先在__init__方法中定义

2）通过定义construct方法来完成神经网络的前向构造。原始模型激活函数为ReLU6，池化模块采用是全局平均池化层。

__all__ = ['MobileNetV2', 'MobileNetV2Backbone', 'MobileNetV2Head', 'mobilenet_v2']

def _make_divisible(v, divisor, min_value=None):
    if min_value is None:
        min_value = divisor
    new_v = max(min_value, int(v + divisor / 2) // divisor * divisor)
    if new_v < 0.9 * v:
        new_v += divisor
    return new_v

class GlobalAvgPooling(nn.Cell):
    """
    Global avg pooling definition.

    Args:

    Returns:
        Tensor, output tensor.

    Examples:
        >>> GlobalAvgPooling()
    """

    def __init__(self):
        super(GlobalAvgPooling, self).__init__()

    def construct(self, x):
        x = P.mean(x, (2, 3))
        return x

class ConvBNReLU(nn.Cell):
    """
    Convolution/Depthwise fused with Batchnorm and ReLU block definition.

    Args:
        in_planes (int): Input channel.
        out_planes (int): Output channel.
        kernel_size (int): Input kernel size.
        stride (int): Stride size for the first convolutional layer. Default: 1.
        groups (int): channel group. Convolution is 1 while Depthiwse is input channel. Default: 1.

    Returns:
        Tensor, output tensor.

    Examples:
        >>> ConvBNReLU(16, 256, kernel_size=1, stride=1, groups=1)
    """

    def __init__(self, in_planes, out_planes, kernel_size=3, stride=1, groups=1):
        super(ConvBNReLU, self).__init__()
        padding = (kernel_size - 1) // 2
        in_channels = in_planes
        out_channels = out_planes
        if groups == 1:
            conv = nn.Conv2d(in_channels, out_channels, kernel_size, stride, pad_mode='pad', padding=padding)
        else:
            out_channels = in_planes
            conv = nn.Conv2d(in_channels, out_channels, kernel_size, stride, pad_mode='pad',
                             padding=padding, group=in_channels)

        layers = [conv, nn.BatchNorm2d(out_planes), nn.ReLU6()]
        self.features = nn.SequentialCell(layers)

    def construct(self, x):
        output = self.features(x)
        return output

class InvertedResidual(nn.Cell):
    """
    Mobilenetv2 residual block definition.

    Args:
        inp (int): Input channel.
        oup (int): Output channel.
        stride (int): Stride size for the first convolutional layer. Default: 1.
        expand_ratio (int): expand ration of input channel

    Returns:
        Tensor, output tensor.

    Examples:
        >>> ResidualBlock(3, 256, 1, 1)
    """

    def __init__(self, inp, oup, stride, expand_ratio):
        super(InvertedResidual, self).__init__()
        assert stride in [1, 2]

        hidden_dim = int(round(inp * expand_ratio))
        self.use_res_connect = stride == 1 and inp == oup

        layers = []
        if expand_ratio != 1:
            layers.append(ConvBNReLU(inp, hidden_dim, kernel_size=1))
        layers.extend([
            ConvBNReLU(hidden_dim, hidden_dim,
                       stride=stride, groups=hidden_dim),
            nn.Conv2d(hidden_dim, oup, kernel_size=1,
                      stride=1, has_bias=False),
            nn.BatchNorm2d(oup),
        ])
        self.conv = nn.SequentialCell(layers)
        self.cast = P.Cast()

    def construct(self, x):
        identity = x
        x = self.conv(x)
        if self.use_res_connect:
            return P.add(identity, x)
        return x

class MobileNetV2Backbone(nn.Cell):
    """
    MobileNetV2 architecture.

    Args:
        class_num (int): number of classes.
        width_mult (int): Channels multiplier for round to 8/16 and others. Default is 1.
        has_dropout (bool): Is dropout used. Default is false
        inverted_residual_setting (list): Inverted residual settings. Default is None
        round_nearest (list): Channel round to . Default is 8
    Returns:
        Tensor, output tensor.

    Examples:
        >>> MobileNetV2(num_classes=1000)
    """

    def __init__(self, width_mult=1., inverted_residual_setting=None, round_nearest=8,
                 input_channel=32, last_channel=1280):
        super(MobileNetV2Backbone, self).__init__()
        block = InvertedResidual
        # setting of inverted residual blocks
        self.cfgs = inverted_residual_setting
        if inverted_residual_setting is None:
            self.cfgs = [
                # t, c, n, s
                [1, 16, 1, 1],
                [6, 24, 2, 2],
                [6, 32, 3, 2],
                [6, 64, 4, 2],
                [6, 96, 3, 1],
                [6, 160, 3, 2],
                [6, 320, 1, 1],
            ]

        # building first layer
        input_channel = _make_divisible(input_channel * width_mult, round_nearest)
        self.out_channels = _make_divisible(last_channel * max(1.0, width_mult), round_nearest)
        features = [ConvBNReLU(3, input_channel, stride=2)]
        # building inverted residual blocks
        for t, c, n, s in self.cfgs:
            output_channel = _make_divisible(c * width_mult, round_nearest)
            for i in range(n):
                stride = s if i == 0 else 1
                features.append(block(input_channel, output_channel, stride, expand_ratio=t))
                input_channel = output_channel
        features.append(ConvBNReLU(input_channel, self.out_channels, kernel_size=1))
        self.features = nn.SequentialCell(features)
        self._initialize_weights()

    def construct(self, x):
        x = self.features(x)
        return x

    def _initialize_weights(self):
        """
        Initialize weights.

        Args:

        Returns:
            None.

        Examples:
            >>> _initialize_weights()
        """
        self.init_parameters_data()
        for _, m in self.cells_and_names():
            if isinstance(m, nn.Conv2d):
                n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
                m.weight.set_data(Tensor(np.random.normal(0, np.sqrt(2. / n),
                                                          m.weight.data.shape).astype("float32")))
                if m.bias is not None:
                    m.bias.set_data(
                        Tensor(np.zeros(m.bias.data.shape, dtype="float32")))
            elif isinstance(m, nn.BatchNorm2d):
                m.gamma.set_data(
                    Tensor(np.ones(m.gamma.data.shape, dtype="float32")))
                m.beta.set_data(
                    Tensor(np.zeros(m.beta.data.shape, dtype="float32")))

    @property
    def get_features(self):
        return self.features

class MobileNetV2Head(nn.Cell):
    """
    MobileNetV2 architecture.

    Args:
        class_num (int): Number of classes. Default is 1000.
        has_dropout (bool): Is dropout used. Default is false
    Returns:
        Tensor, output tensor.

    Examples:
        >>> MobileNetV2(num_classes=1000)
    """

    def __init__(self, input_channel=1280, num_classes=1000, has_dropout=False, activation="None"):
        super(MobileNetV2Head, self).__init__()
        # mobilenet head
        head = ([GlobalAvgPooling(), nn.Dense(input_channel, num_classes, has_bias=True)] if not has_dropout else
                [GlobalAvgPooling(), nn.Dropout(0.2), nn.Dense(input_channel, num_classes, has_bias=True)])
        self.head = nn.SequentialCell(head)
        self.need_activation = True
        if activation == "Sigmoid":
            self.activation = nn.Sigmoid()
        elif activation == "Softmax":
            self.activation = nn.Softmax()
        else:
            self.need_activation = False
        self._initialize_weights()

    def construct(self, x):
        x = self.head(x)
        if self.need_activation:
            x = self.activation(x)
        return x

    def _initialize_weights(self):
        """
        Initialize weights.

        Args:

        Returns:
            None.

        Examples:
            >>> _initialize_weights()
        """
        self.init_parameters_data()
        for _, m in self.cells_and_names():
            if isinstance(m, nn.Dense):
                m.weight.set_data(Tensor(np.random.normal(
                    0, 0.01, m.weight.data.shape).astype("float32")))
                if m.bias is not None:
                    m.bias.set_data(
                        Tensor(np.zeros(m.bias.data.shape, dtype="float32")))
    @property
    def get_head(self):
        return self.head

class MobileNetV2(nn.Cell):
    """
    MobileNetV2 architecture.

    Args:
        class_num (int): number of classes.
        width_mult (int): Channels multiplier for round to 8/16 and others. Default is 1.
        has_dropout (bool): Is dropout used. Default is false
        inverted_residual_setting (list): Inverted residual settings. Default is None
        round_nearest (list): Channel round to . Default is 8
    Returns:
        Tensor, output tensor.

    Examples:
        >>> MobileNetV2(backbone, head)
    """

    def __init__(self, num_classes=1000, width_mult=1., has_dropout=False, inverted_residual_setting=None, \
        round_nearest=8, input_channel=32, last_channel=1280):
        super(MobileNetV2, self).__init__()
        self.backbone = MobileNetV2Backbone(width_mult=width_mult, \
            inverted_residual_setting=inverted_residual_setting, \
            round_nearest=round_nearest, input_channel=input_channel, last_channel=last_channel).get_features
        self.head = MobileNetV2Head(input_channel=self.backbone.out_channel, num_classes=num_classes, \
            has_dropout=has_dropout).get_head

    def construct(self, x):
        x = self.backbone(x)
        x = self.head(x)
        return x

class MobileNetV2Combine(nn.Cell):
    """
    MobileNetV2Combine architecture.

    Args:
        backbone (Cell): the features extract layers.
        head (Cell):  the fully connected layers.
    Returns:
        Tensor, output tensor.

    Examples:
        >>> MobileNetV2(num_classes=1000)
    """

    def __init__(self, backbone, head):
        super(MobileNetV2Combine, self).__init__(auto_prefix=False)
        self.backbone = backbone
        self.head = head

    def construct(self, x):
        x = self.backbone(x)
        x = self.head(x)
        return x

def mobilenet_v2(backbone, head):
    return MobileNetV2Combine(backbone, head)

MobileNetV2模型的训练与测试

一般情况下，模型训练时采用静态学习率，如0.01。随着训练步数的增加，模型逐渐趋于收敛，对权重参数的更新幅度应该逐渐降低，以减小模型训练后期的抖动。所以，模型训练时可以采用动态下降的学习率，常见的学习率下降策略有：

• polynomial decay/square decay;
• cosine decay;
• exponential decay;
• stage decay.

本次使用cosine decay下降策略，如下代码：

def cosine_decay(total_steps, lr_init=0.0, lr_end=0.0, lr_max=0.1, warmup_steps=0):
    """
    Applies cosine decay to generate learning rate array.

    Args:
       total_steps(int): all steps in training.
       lr_init(float): init learning rate.
       lr_end(float): end learning rate
       lr_max(float): max learning rate.
       warmup_steps(int): all steps in warmup epochs.

    Returns:
       list, learning rate array.
    """
    lr_init, lr_end, lr_max = float(lr_init), float(lr_end), float(lr_max)
    decay_steps = total_steps - warmup_steps
    lr_all_steps = []
    inc_per_step = (lr_max - lr_init) / warmup_steps if warmup_steps else 0
    for i in range(total_steps):
        if i < warmup_steps:
            lr = lr_init + inc_per_step * (i + 1)
        else:
            cosine_decay = 0.5 * (1 + math.cos(math.pi * (i - warmup_steps) / decay_steps))
            lr = (lr_max - lr_end) * cosine_decay + lr_end
        lr_all_steps.append(lr)

    return lr_all_steps

模型训练过程中，可以添加检查点（Checkpoint）用于保存模型的参数，以便进行推理及中断后再训练使用。使用场景如下：

• 训练后推理场景
• 再训练场景（防止长时间的训练任务异常退出； 微调场景）

这里加载ImageNet数据上预训练的MobileNetv2进行Fine-tuning，只训练最后修改的FC层，并在训练过程中保存Checkpoint。

def switch_precision(net, data_type):
    if ms.get_context('device_target') == "Ascend":
        net.to_float(data_type)
        for _, cell in net.cells_and_names():
            if isinstance(cell, nn.Dense):
                cell.to_float(ms.float32)

模型训练与测试

训练之前，定义训练函数，读取数据并对模型进行实例化，定义优化器和损失函数。

在训练MobileNetV2之前对MobileNetV2Backbone层的参数进行了固定，使其在训练过程中对该模块的权重参数不进行更新；只对MobileNetV2Head模块的参数进行更新。

from mindspore.amp import FixedLossScaleManager
import time
LOSS_SCALE = 1024

train_dataset = create_dataset(dataset_path=config.dataset_path, config=config)
eval_dataset = create_dataset(dataset_path=config.dataset_path, config=config)
step_size = train_dataset.get_dataset_size()
    
backbone = MobileNetV2Backbone() #last_channel=config.backbone_out_channels
# Freeze parameters of backbone. You can comment these two lines.
for param in backbone.get_parameters():
    param.requires_grad = False
# load parameters from pretrained model
load_checkpoint(config.pretrained_ckpt, backbone)

head = MobileNetV2Head(input_channel=backbone.out_channels, num_classes=config.num_classes)
network = mobilenet_v2(backbone, head)

# define loss, optimizer, and model
loss = nn.SoftmaxCrossEntropyWithLogits(sparse=True, reduction='mean')
loss_scale = FixedLossScaleManager(LOSS_SCALE, drop_overflow_update=False)
lrs = cosine_decay(config.epochs * step_size, lr_max=config.lr_max)
opt = nn.Momentum(network.trainable_params(), lrs, config.momentum, config.weight_decay, loss_scale=LOSS_SCALE)

# 定义用于训练的train_loop函数。
def train_loop(model, dataset, loss_fn, optimizer):
    # 定义正向计算函数
    def forward_fn(data, label):
        logits = model(data)
        loss = loss_fn(logits, label)
        return loss

    # 定义微分函数，使用mindspore.value_and_grad获得微分函数grad_fn,输出loss和梯度。
    # 由于是对模型参数求导,grad_position 配置为None，传入可训练参数。
    grad_fn = ms.value_and_grad(forward_fn, None, optimizer.parameters)

    # 定义 one-step training函数
    def train_step(data, label):
        loss, grads = grad_fn(data, label)
        optimizer(grads)
        return loss

    size = dataset.get_dataset_size()
    model.set_train()
    for batch, (data, label) in enumerate(dataset.create_tuple_iterator()):
        loss = train_step(data, label)

        if batch % 10 == 0:
            loss, current = loss.asnumpy(), batch
            print(f"loss: {loss:>7f}  [{current:>3d}/{size:>3d}]")

# 定义用于测试的test_loop函数。
def test_loop(model, dataset, loss_fn):
    num_batches = dataset.get_dataset_size()
    model.set_train(False)
    total, test_loss, correct = 0, 0, 0
    for data, label in dataset.create_tuple_iterator():
        pred = model(data)
        total += len(data)
        test_loss += loss_fn(pred, label).asnumpy()
        correct += (pred.argmax(1) == label).asnumpy().sum()
    test_loss /= num_batches
    correct /= total
    print(f"Test: \n Accuracy: {(100*correct):>0.1f}%, Avg loss: {test_loss:>8f} \n")

print("============== Starting Training ==============")
# 由于时间问题，训练过程只进行了2个epoch ，可以根据需求调整。
epoch_begin_time = time.time()
epochs = 2
for t in range(epochs):
    begin_time = time.time()
    print(f"Epoch {t+1}\n-------------------------------")
    train_loop(network, train_dataset, loss, opt)
    ms.save_checkpoint(network, "save_mobilenetV2_model.ckpt")
    end_time = time.time()
    times = end_time - begin_time
    print(f"per epoch time: {times}s")
    test_loop(network, eval_dataset, loss)
epoch_end_time = time.time()
times = epoch_end_time - epoch_begin_time
print(f"total time:  {times}s")
print("============== Training Success ==============")

训练过程

没有占用gpu显存（是英伟达的4090）.

模型推理

加载模型Checkpoint进行推理，使用load_checkpoint接口加载数据时，需要把数据传入给原始网络，而不能传递给带有优化器和损失函数的训练网络。

CKPT="save_mobilenetV2_model.ckpt"

def image_process(image):
    """Precess one image per time.
    
    Args:
        image: shape (H, W, C)
    """
    mean=[0.485*255, 0.456*255, 0.406*255]
    std=[0.229*255, 0.224*255, 0.225*255]
    image = (np.array(image) - mean) / std
    image = image.transpose((2,0,1))
    img_tensor = Tensor(np.array([image], np.float32))
    return img_tensor

def infer_one(network, image_path):
    image = Image.open(image_path).resize((config.image_height, config.image_width))
    logits = network(image_process(image))
    pred = np.argmax(logits.asnumpy(), axis=1)[0]
    print(image_path, class_en[pred])

def infer():
    backbone = MobileNetV2Backbone(last_channel=config.backbone_out_channels)
    head = MobileNetV2Head(input_channel=backbone.out_channels, num_classes=config.num_classes)
    network = mobilenet_v2(backbone, head)
    load_checkpoint(CKPT, network)
    for i in range(91, 100):
        infer_one(network, f'data_en/test/Cardboard/000{i}.jpg')
infer()

导出AIR/GEIR/ONNX模型文件

导出AIR模型文件，用于后续Atlas 200 DK上的模型转换与推理。当前仅支持MindSpore+Ascend环境。

backbone = MobileNetV2Backbone(last_channel=config.backbone_out_channels)
head = MobileNetV2Head(input_channel=backbone.out_channels, num_classes=config.num_classes)
network = mobilenet_v2(backbone, head)
load_checkpoint(CKPT, network)

input = np.random.uniform(0.0, 1.0, size=[1, 3, 224, 224]).astype(np.float32)
# export(network, Tensor(input), file_name='mobilenetv2.air', file_format='AIR')
# export(network, Tensor(input), file_name='mobilenetv2.pb', file_format='GEIR')
export(network, Tensor(input), file_name='mobilenetv2.onnx', file_format='ONNX')