写一个对输入的图像进行哈夫曼编码,显示原图像的熵,编码后的平均码字长度及编码效率的代码
时间: 2024-03-10 11:48:25 浏览: 20
好的,这里提供一个Python实现的哈夫曼编码及计算图像熵和编码效率的代码,需要使用到Python的numpy和heapq库:
```python
import numpy as np
import heapq
# 计算图像熵
def calc_entropy(img):
# 将图像转为一维数组
img = img.flatten()
# 计算出现频率
hist, _ = np.histogram(img, bins=256, range=(0, 255))
hist = hist.astype(float) / img.size
# 计算熵
entropy = -np.sum(hist * np.log2(hist + (hist==0)))
return entropy
# 构建哈夫曼树
def build_huffman_tree(freq):
heap = [[wt, [idx, '']] for idx, wt in enumerate(freq)]
heapq.heapify(heap)
while len(heap) > 1:
lo = heapq.heappop(heap)
hi = heapq.heappop(heap)
for pair in lo[1:]:
pair[1] = '0' + pair[1]
for pair in hi[1:]:
pair[1] = '1' + pair[1]
heapq.heappush(heap, [lo[0] + hi[0]] + lo[1:] + hi[1:])
return sorted(heapq.heappop(heap)[1:], key=lambda p: (len(p[-1]), p))
# 对图像进行哈夫曼编码
def huffman_encode(img):
# 将图像转为一维数组
img = img.flatten()
# 计算出现频率
hist, _ = np.histogram(img, bins=256, range=(0, 255))
hist = hist.astype(float) / img.size
# 构建哈夫曼树
codes = build_huffman_tree(hist)
# 生成编码表
code_dict = dict(codes)
# 对每个灰度值进行编码
encoded_img = ''
for pixel in img:
encoded_img += code_dict[pixel]
return encoded_img, codes
# 计算编码效率
def calc_efficiency(img, encoded_img, codes):
# 计算原图像熵
entropy = calc_entropy(img)
# 计算编码后的平均码字长度
avg_len = np.mean([len(code[1]) for code in codes])
# 计算编码效率
efficiency = entropy / avg_len
return entropy, avg_len, efficiency
```
使用方法如下:
```python
import cv2
# 读取图像
img = cv2.imread('example.jpg', 0)
# 进行哈夫曼编码
encoded_img, codes = huffman_encode(img)
# 计算图像熵和编码效率
entropy, avg_len, efficiency = calc_efficiency(img, encoded_img, codes)
# 打印结果
print('原图像熵:', entropy)
print('编码后平均码字长度:', avg_len)
print('编码效率:', efficiency)
```
需要注意的是,上述代码中的`example.jpg`需要替换为你自己的图像文件名。