AttributeError：'numpy.ndarray'对象没有属性'append'：图像处理示例

Question

I will first explain what I want to do. I have an image and I want to store the pixel values for a specific ROI. For that reason I implement the following loop(found in another topic of the site):

pixels = im.load() 

all_pixels = []
for x in range(SpecificWidth):
  for y in range(SpecificHeight):
    cpixel = pixels[x, y]
    all_pixels.append(cpixel)

However, it does not return a SpecificwidthXSpecificHeight matrix but one of length as much as the values. Because I want to keep the size of the matrix of the ROI I implement the following loop(much the same with the previous):

array=np.array(all_pixels)
roi_pixels = np.zeros((SpecificWidth,SpecificHeight))

for i in range(0,array.shape[0],width):
    c_roi_pixels=all_pixels[i]
    roi_pixels.append(c_roi_pixels)

And I have the error as it mentioned in the title.

Answer 1

In numpy, append is a function , not a method .

So you should use eg:

roi_pixels = np.append(roi_pixels, c_roi_pixels)

Note that the append function creates and returns a copy! It does not modify the original.

Answer 2

@RolandSmith is absolutely right about the cause of the error message you're seeing. A much more efficient way to achieve what you're trying to do is to convert the whole image to a numpy array, then use slice indexing to get the pixels corresponding to your ROI:

# convert the image to a numpy array
allpix = np.array(im)

# array of zeros to hold the ROI pixels
roipix = np.zeros_like(allpix)

# copy the ROI region using slice indexing
roipix[:SpecificHeight, :SpecificWidth] = allpix[:SpecificHeight, :SpecificWidth]