Moving text lower one image at a time in a loop, using PIL

Question

I am new to PIL. I am attempting to save multiple images in a loop in order to change the position of the text in each image.

Here is my code:

from PIL import Image, ImageDraw, ImageFont
import os

files = []
C = 0
base = Image.open('car.jpg').convert('RGBA')

txt = Image.new('RGBA', base.size, (255,255,255,0))

fnt = ImageFont.truetype('calibrib.ttf', 40)
d = ImageDraw.Draw(txt)

W = 0
while C < 175:
    d.text((0,W), "Test Text", font=fnt, fill=(255,255,255,255))
    out = Image.alpha_composite(base, txt)

    f = (3-len(str(C)))*'0'+str(C)
    folder = os.getcwd()
    out.save(folder + '/images/a%s.png' % f, "PNG")
    files.append('a%s.png' % f)

    W = W+1
    C =  C+1

This is how the first output image looks like:

My desired output is to see "Test Text" centered vertically in the last image.

The text should move lower and lower one image at a time in the loop.

But, instead I get this:

Answer 1

the ImageDraw.Draw call makes txt an image to be drawn on in place, each time you call d.text you are drawing new text on the txt image without removing the previous text from the last iterations. To fix this you need to reset the txt object on each iteration. You can do this by calling

txt = Image.new('RGBA', base.size, (255,255,255,0))
d = ImageDraw.Draw(txt)

inside the while loop.