Trial and error to speed up heat map generation

I was making a program to calculate a heat map (RGB) from a value that takes 0 to 255. The source I wrote first (GPU + Cupy) was too slow, so I will leave the result of trial and error.

** * cv2.applyColorMap (grayscale_image, cv2.COLORMAP_JET) solved everything, but I made it myself (shame). ** **

The following is the processing for the image size 320x180. The code is only the main part. In addition, the heat map is a simplified version (trigonometric function not used) to obtain the approximate value. (Linear diagram of Convert value magnitude to thermography-like color).

GPU+Cupy(for) This is the code I originally wrote. It is a losing group code that is processed by turning it with for honestly.

    def conv_v_to_heat(v):
        image = cuda.cupy.zeros((v.shape[0], array.v[1], 4))
        for i, w in enumerate(image):
            for j, h in enumerate(w):
                image[i,j,0] = get_heat_r(array[i][j])
                image[i,j,1] = get_heat_g(array[i][j])
                image[i,j,2] = get_heat_b(array[i][j])
                image[i,j,3] = array[i][j] #Alpha is suitable

    def get_heat_r(v):
        if v <= 127:
            return 0
        elif v <= 190:
            return (v-127)*4
        else:
            return 255

sec: 20.43495798110962

CPU+Numpy(for) Isn't it better to stop using the GPU than to use for? I changed it to CPU (source omitted).

sec: 0.6369609832763672

The CPU was faster at all.

CPU+Numba+Numpy(for) I put Numba.

    @jit
    def conv_v_to_heat(v):

    @jit
    def get_heat_r(v):

sec: 0.20061397552490234

It's even faster.

CPU+Numba+Numpy(filter) In the first place, it is a loser when using for for Numpy, so I tried to deal with it by filtering.

    def conv_v_to_heat(v):
       image = np.zeros((v.shape[0], v.shape[1], 4))
        image[:, :, 0] = get_r(array)
        image[:, :, 1] = get_g(array)
        image[:, :, 2] = get_b(array)
        image[:, :, 3] = v

    def get_heat_r(v):
        out = np.zeros((v.shape))
        out[...] = 255
        out[(v<=190)] = (v[(v<=190)]-127)*4
        out[(v<=127)] = 0
        return out

sec: 0.0013210773468017578

It's overwhelmingly faster.

CPU+Numpy(filter) As a test, I will remove Numba.

sec: 0.001230478286743164

That's faster. Rather, it is an error level.

GPU+Cupy(filter) Then what about GPU?

sec: 0.008527278900146484

I am late.

Summary

CPU + Numpy (filter) was the best. I think there is a faster implementation, but personally it's a satisfying speed. After all, if you use for, you will lose.