Keras Python Multi Image Input shape error

问题

I am trying to teach myself to build a CNN that takes more than one image as an input. Since the dataset I created to test this is large and in the long run I hope to solve a problem involving a very large dataset, I am using a generator to read images into arrays which I am passing to Keras Model's fit_generator function.

When I run my generator in isolation it works fine, and produces outputs of the appropriate shape. It yields a tuple containing two entries, the first of which has shape (4, 100, 100, 1) and the second of which has shape (4, ).

Reading about multiple input Keras CNNs has given me the impression that this is the right format for a generator for a 4 input CNN that is identifying which of the 4 inputs contains an image.

However, when I run the code I get:

"ValueError: Error when checking input: expected input_121 to have 4 dimensions, but got array with shape (100, 100, 1)"

I've been searching for a solution for some time now and I suspect that the problem lies in getting my (100, 100, 1) shape arrays to be sent to the Inputs as (None, 100, 100, 1) shape arrays.

But when I tried to modify the output of my generator I get an error about having dimension 5, which makes sense as an error because the output of the generator should have the form X, y = [X1, X2, X3, X4], [a, b, c, d], where Xn has shape (100, 100, 1), and a/b/c/d are numbers.

Here is the code:

https://gist.github.com/anonymous/d283494aee982fbc30f3b52f2a6f422c

Thanks in advance!

回答1:

You are creating a list of arrays in your generator with the wrong dimensions.

If you want the correct shape, reshape individual images to have the 4 dimensions: (n_samples, x_size, y_size, n_bands) your model will work. In your case you should reshape your images to (1, 100, 100, 1).

At the end stack them with np.vstack. The generator will yield an array of shape (4, 100, 100, 1).

Check if this adapted code works

def input_generator(folder, directories):

    Streams = []
    for i in range(len(directories)):
        Streams.append(os.listdir(folder + "/" + directories[i]))
        for j in range(len(Streams[i])):
            Streams[i][j] = "Stream" + str(i + 1) + "/" + Streams[i][j]   
        Streams[i].sort()


    length = len(Streams[0])
    index = 0
    while True:
        X = []
        y = np.zeros(4)
        for Stream in Streams:
            image = load_img(folder + '/' + Stream[index], grayscale = True)
            array = img_to_array(image).reshape((1,100,100,1))
            X.append(array)
        y[int(Stream[index][15]) - 1] = 1
        index += 1
        index = index % length
        yield np.vstack(X), y

来源：https://stackoverflow.com/questions/44399299/keras-python-multi-image-input-shape-error