python cv2圖像質量壓縮的算法示例
使用opencv對圖像進行編碼,一方面是圖像二進制傳輸的需要,另一方面對圖像壓縮。以jpeg壓縮為例:
1、轉為二進制編碼
img = cv2.imread(img_path) # 取值范圍:0~100,數值越小,壓縮比越高,圖片質量損失越嚴重 params = [cv2.IMWRITE_JPEG_QUALITY, ratio] # ratio:0~100 msg = cv2.imencode(".jpg", img, params)[1] msg = (np.array(msg)).tobytes() print("msg:", len(msg))
對於png壓縮,改為:
# 取值范圍:0~9,數值越小,壓縮比越低,圖片質量越高 params = [cv2.IMWRITE_PNG_COMPRESSION, ratio] # ratio: 0~9 msg = cv2.imencode(".png", img, params)[1] msg = (np.array(msg)).tobytes()
對於圖像解碼,使用imdecode即可解為numpy類型圖像:
img = cv2.imdecode(np.frombuffer(msg, np.uint8), cv2.IMREAD_COLOR) print(img.shape, type(img))
2、圖像質量壓縮
原圖(48k):
jpg壓縮:
img_path = r"E:\img.jpg" img = cv2.imread(img_path) cv2.imwrite(r"E:\ret_80.jpg", img, [cv2.IMWRITE_JPEG_QUALITY, 80]) cv2.imwrite(r"E:\ret_40.jpg", img, [cv2.IMWRITE_JPEG_QUALITY, 40]) cv2.imwrite(r"E:\ret_10.jpg", img, [cv2.IMWRITE_JPEG_QUALITY, 10]) cv2.imwrite(r"E:\ret_0.jpg", img, [cv2.IMWRITE_JPEG_QUALITY, 0])
結果:
壓縮後圖像大小依次為:49.6K、25.6K、11K、5.02K。jpg壓縮明顯,壓縮到極致時顏色信息損失嚴重。
png壓縮:
img_path = r"E:\img.jpg" img = cv2.imread(img_path) cv2.imwrite(r"E:\ret_0.png", img, [cv2.IMWRITE_PNG_COMPRESSION, 0]) cv2.imwrite(r"E:\ret_3.png", img, [cv2.IMWRITE_PNG_COMPRESSION, 3]) cv2.imwrite(r"E:\ret_6.png", img, [cv2.IMWRITE_PNG_COMPRESSION, 6]) cv2.imwrite(r"E:\ret_9.png", img, [cv2.IMWRITE_PNG_COMPRESSION, 9])
結果:
壓縮後圖像大小依次為:675K、364K、364K、360K。png格式偏大,壓縮率調到最高也還有360K,且成像上無明顯變化。
PS:也可以對圖像壓縮後保存,如:
img_path = r"E:\img.jpg" img = cv2.imread(img_path) params = [cv2.IMWRITE_PNG_COMPRESSION, 0] msg = cv2.imencode(".png", img, params)[1] msg = (np.array(msg)).tobytes() print("msg:", len(msg)) img = cv2.imdecode(np.frombuffer(msg, np.uint8), cv2.IMREAD_COLOR) cv2.imwrite(rr"E:\ret.jpg", img)
bug處理:
早期版本這樣寫:
msg = (np.array(msg)).tostring() 改為: msg = (np.array(msg)).tobytes() img = cv2.imdecode(np.fromstring(msg, np.uint8), cv2.IMREAD_COLOR) 改為: img = cv2.imdecode(np.frombuffer(msg, np.uint8), cv2.IMREAD_COLOR)
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