12. Image masks
12.1. Masks
Masks are commonly used in advanced Photo-editing techniques.
Masks are a list of values used to adjust the brightness of each pixel.
The sample mask below is an array made up of 5 lists of 5 values.
It is generally easier to lay the mask out in the 5 by 5 pattern like the LEDS on the microbit.
down_right_mask = [
[9, 8, 7, 6, 5],
[8, 7, 6, 5, 4],
[7, 6, 5, 4, 3],
[6, 5, 4, 3, 2],
[5, 4, 3, 2, 1],
]
Each value in the array is designed to be multiplied by the corresponding pixel brightness (then divided by 9) to get new pixel brightnesses.
The value for each pixel can be obtained using list indexing.
Using an index of 0, down_right_mask[0] gives the list, [9, 8, 7, 6, 5].
Using an index of 1 on this list, down_right_mask[0][1], gives 8.
Each indexed value in the array, array[y][x] corresponds to a pixel at position x, y.
The function, get_masked_image_array(img, mask), takes an image, img, gets its image array using get_image_array(img), does the multiplications and returns an image array.
from microbit import *
def get_image_array(img):
img_repr = repr(img)
img_str = img_repr[7:-3]
img_str = img_str.replace(":", "")
img_array = [int(x) for x in img_str]
return img_array
def get_masked_image_array(img, mask):
img_array = get_image_array(img)
masked_img_array = list()
for y in range(5):
for x in range(5):
mask_val = mask[y][x]
img_val = img_array[y * 5 + x]
new_img_val = min(9, int(mask_val * img_val / 9))
masked_img_array.append(new_img_val)
return masked_img_array
Finally, get_masked_image(img, mask), put these steps together and returns the masked image.
from microbit import *
def get_masked_image(img, mask):
masked_img_array = get_masked_image_array(img, mask)
return Image(5, 5, bytearray(masked_img_array))
The example below applies the down_right_mask mask to the TSHIRT image.
from microbit import *
def get_image_array(img):
img_repr = repr(img)
img_str = img_repr[7:-3]
img_str = img_str.replace(":", "")
img_array = [int(x) for x in img_str]
return img_array
def get_masked_image_array(img, mask):
img_array = get_image_array(img)
masked_img_array = list()
for y in range(5):
for x in range(5):
mask_val = mask[y][x]
img_val = img_array[y * 5 + x]
new_img_val = min(9, int(mask_val * img_val / 9))
masked_img_array.append(new_img_val)
return masked_img_array
def get_masked_image(img, mask):
masked_img_array = get_masked_image_array(img, mask)
return Image(5, 5, bytearray(masked_img_array))
down_right_mask = [
[9, 8, 7, 6, 5],
[8, 7, 6, 5, 4],
[7, 6, 5, 4, 3],
[6, 5, 4, 3, 2],
[5, 4, 3, 2, 1],
]
img = Image.TSHIRT
while True:
img_masked = get_masked_image(img, down_right_mask)
display.show(img)
sleep(800)
display.show(img_masked)
sleep(800)
12.2. Example Masks
Some sample masks are provided here.
right_mask = [
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
]
left_mask = [
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
]
down_mask = [
[9, 9, 9, 9, 9],
[7, 7, 7, 7, 7],
[5, 5, 5, 5, 5],
[3, 3, 3, 3, 3],
[1, 1, 1, 1, 1],
]
up_mask = [
[1, 1, 1, 1, 1],
[3, 3, 3, 3, 3],
[5, 5, 5, 5, 5],
[7, 7, 7, 7, 7],
[9, 9, 9, 9, 9],
]
outwards_mask = [
[4, 4, 4, 4, 4],
[4, 7, 7, 7, 4],
[4, 7, 9, 7, 4],
[4, 7, 7, 7, 4],
[4, 4, 4, 4, 4],
]
inwards_mask = [
[9, 9, 9, 9, 9],
[9, 7, 7, 7, 9],
[9, 7, 4, 7, 9],
[9, 7, 7, 7, 9],
[9, 9, 9, 9, 9],
]
duller1_mask = [
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
]
duller5_mask = [
[5, 5, 5, 5, 5],
[5, 5, 5, 5, 5],
[5, 5, 5, 5, 5],
[5, 5, 5, 5, 5],
[5, 5, 5, 5, 5],
]
Tasks
Write code to apply a right mask to PACMAN.
Write code to apply a left mask to GHOST.
Write code to apply a up mask to RABBIT.
Write code to apply a down mask to PITCHFORK.
Write code to apply a right mask to PACMAN.
from microbit import *
def get_image_array(img):
img_repr = repr(img)
img_str = img_repr[7:-3]
img_str = img_str.replace(":", "")
img_array = [int(x) for x in img_str]
return img_array
def get_mask_image_array(img, mask):
img_array = get_image_array(img)
masked_img_array = list()
for y in range(5):
for x in range(5):
mask_val = mask[y][x]
img_val = img_array[y * 5 + x]
new_img_val = min(9, int(mask_val * img_val / 9))
masked_img_array.append(new_img_val)
return masked_img_array
def get_masked_image(img, mask):
masked_img_array = get_mask_image_array(img, mask)
return Image(5, 5, bytearray(masked_img_array))
mask = [
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
]
img = Image.PACMAN
while True:
img_masked = get_masked_image(img, mask)
display.show(img)
sleep(800)
display.show(img_masked)
sleep(800)
Write code to apply a left mask to GHOST.
from microbit import *
def get_image_array(img):
img_repr = repr(img)
img_str = img_repr[7:-3]
img_str = img_str.replace(":", "")
img_array = [int(x) for x in img_str]
return img_array
def get_mask_image_array(img, mask):
img_array = get_image_array(img)
masked_img_array = list()
for y in range(5):
for x in range(5):
mask_val = mask[y][x]
img_val = img_array[y * 5 + x]
new_img_val = min(9, int(mask_val * img_val / 9))
masked_img_array.append(new_img_val)
return masked_img_array
def get_masked_image(img, mask):
masked_img_array = get_mask_image_array(img, mask)
return Image(5, 5, bytearray(masked_img_array))
mask = [
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
]
img = Image.GHOST
while True:
img_masked = get_masked_image(img, mask)
display.show(img)
sleep(800)
display.show(img_masked)
sleep(800)
Write code to apply a up mask to RABBIT.
from microbit import *
def get_image_array(img):
img_repr = repr(img)
img_str = img_repr[7:-3]
img_str = img_str.replace(":", "")
img_array = [int(x) for x in img_str]
return img_array
def get_mask_image_array(img, mask):
img_array = get_image_array(img)
masked_img_array = list()
for y in range(5):
for x in range(5):
mask_val = mask[y][x]
img_val = img_array[y * 5 + x]
new_img_val = min(9, int(mask_val * img_val / 9))
masked_img_array.append(new_img_val)
return masked_img_array
def get_masked_image(img, mask):
masked_img_array = get_mask_image_array(img, mask)
return Image(5, 5, bytearray(masked_img_array))
mask = [
[1, 1, 1, 1, 1],
[3, 3, 3, 3, 3],
[5, 5, 5, 5, 5],
[7, 7, 7, 7, 7],
[9, 9, 9, 9, 9],
]
img = Image.RABBIT
while True:
img_masked = get_masked_image(img, mask)
display.show(img)
sleep(800)
display.show(img_masked)
sleep(800)
Write code to apply a down mask to PITCHFORK.
from microbit import *
def get_image_array(img):
img_repr = repr(img)
img_str = img_repr[7:-3]
img_str = img_str.replace(":", "")
img_array = [int(x) for x in img_str]
return img_array
def get_mask_image_array(img, mask):
img_array = get_image_array(img)
masked_img_array = list()
for y in range(5):
for x in range(5):
mask_val = mask[y][x]
img_val = img_array[y * 5 + x]
new_img_val = min(9, int(mask_val * img_val / 9))
masked_img_array.append(new_img_val)
return masked_img_array
def get_masked_image(img, mask):
masked_img_array = get_mask_image_array(img, mask)
return Image(5, 5, bytearray(masked_img_array))
mask = [
[9, 9, 9, 9, 9],
[7, 7, 7, 7, 7],
[5, 5, 5, 5, 5],
[3, 3, 3, 3, 3],
[1, 1, 1, 1, 1],
]
img = Image.PITCHFORK
while True:
img_masked = get_masked_image(img, mask)
display.show(img)
sleep(800)
display.show(img_masked)
sleep(800)
12.3. Mask loops
A list of mask names can be created.
mask_names = [left_mask, right_mask]
A for-loop can be used to loop through the list and apply each mask to an image.
Tasks
Write code to loop though a list of 9 mask names and apply them to a TSHIRT image.
Write code to loop though a list of 9 mask names and apply them to a TSHIRT image.
from microbit import *
down_right_mask = [
[9, 8, 7, 6, 5],
[8, 7, 6, 5, 4],
[7, 6, 5, 4, 3],
[6, 5, 4, 3, 2],
[5, 4, 3, 2, 1],
]
right_mask = [
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
[9, 7, 5, 3, 1],
]
left_mask = [
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
[1, 3, 5, 7, 9],
]
down_mask = [
[9, 9, 9, 9, 9],
[7, 7, 7, 7, 7],
[5, 5, 5, 5, 5],
[3, 3, 3, 3, 3],
[1, 1, 1, 1, 1],
]
up_mask = [
[1, 1, 1, 1, 1],
[3, 3, 3, 3, 3],
[5, 5, 5, 5, 5],
[7, 7, 7, 7, 7],
[9, 9, 9, 9, 9],
]
outwards_mask = [
[4, 4, 4, 4, 4],
[4, 7, 7, 7, 4],
[4, 7, 9, 7, 4],
[4, 7, 7, 7, 4],
[4, 4, 4, 4, 4],
]
inwards_mask = [
[9, 9, 9, 9, 9],
[9, 7, 7, 7, 9],
[9, 7, 4, 7, 9],
[9, 7, 7, 7, 9],
[9, 9, 9, 9, 9],
]
duller5_mask = [
[5, 5, 5, 5, 5],
[5, 5, 5, 5, 5],
[5, 5, 5, 5, 5],
[5, 5, 5, 5, 5],
[5, 5, 5, 5, 5],
]
duller1_mask = [
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
]
def get_image_array(img):
img_repr = repr(img)
img_str = img_repr[7:-3]
img_str = img_str.replace(":", "")
img_array = [int(x) for x in img_str]
return img_array
def get_mask_image_array(img, mask):
img_array = get_image_array(img)
masked_img_array = list()
for y in range(5):
for x in range(5):
mask_val = mask[y][x]
img_val = img_array[y * 5 + x]
new_img_val = min(9, int(mask_val * img_val / 9))
masked_img_array.append(new_img_val)
return masked_img_array
def get_masked_image(img, mask):
masked_img_array = get_mask_image_array(img, mask)
return Image(5, 5, bytearray(masked_img_array))
mask_names = [
down_right_mask,
left_mask,
right_mask,
up_mask,
down_mask,
outwards_mask,
inwards_mask,
duller5_mask,
duller1_mask,
]
img = Image.TSHIRT
while True:
display.show(img)
sleep(400)
for mask in mask_names:
img_masked = get_masked_image(img, mask)
display.show(img_masked)
sleep(200)