Opencv+Python cv2.imwrite（）和简历imshow两个图像显示不同的输出

Question

我使用Opencv（3.0）和python2.7进行图像处理，但是cv2.imwrite()和{}有问题。它们产生不同的输出，我的代码如下：

tfinal = (255)*(nir_img-red_img)/(nir_img+red_img)
cv2.imwrite(_db_img1+'_NDVI'+_ext_img,tfinal)
cv2.imshow('NDVI',tfinal)

第一个图像是cv2.imshow()的输出

第二个图像是cv2.imwrite()的输出

Answer 1

感谢梅尔尼科夫·谢尔盖简要介绍了我的解决方案。 我已经解决了这个问题使用以下语法修改在我的程序。 当我写我的图像乘以255，我得到了同样的结果。在

tfinal = (255)*(nir_img-red_img)/(nir_img+red_img)
cv2.imwrite(_db_img1+'_NDVI'+_ext_img,tfinal*255)
cv2.imshow('NDVI',tfinal)

Answer 2

这可能是因为您的数据类型。imwrite和imshow根据数据类型自动决定如何处理数据。如imwrite和imshow的文档所述：

imwrite：

The function imwrite saves the image to the specified file. The image format is chosen based on the filename extension (see imread() for the list of extensions). Only 8-bit (or 16-bit unsigned (CV_16U) in case of PNG, JPEG 2000, and TIFF) single-channel or 3-channel (with ‘BGR’ channel order) images can be saved using this function.

imshow：

The function may scale the image, depending on its depth:

• If the image is 8-bit unsigned, it is displayed as is.
• If the image is 16-bit unsigned or 32-bit integer, the pixels are divided by 256. That is, the value range [0,255*256] is mapped to [0,255].
• If the image is 32-bit floating-point, the pixel values are multiplied by
  255. That is, the value range [0,1] is mapped to [0,255].

因此，您的底层数据类型似乎不是无符号字符，而是float或32位整数。在

此外，由于操作优先级，您可能会遇到以下问题：

(255)*(nir_img-red_img)/(nir_img+red_img)

你可能会溢出。最好将值设置在[0；1]的范围内，而不是将其相乘：

(255) * ( (nir_img-red_img)/(nir_img+red_img) )