identify not white pixels in bmp

[flash77]

Hi,

sorry for not spotting the error, I didn't expect it there and overread it.

Unfortunately I don't know how to deal with a grainy scan. Testing "clean" color bitmaps worked fine.
Perhaps it is possible to count rgb values which are nearly the same. I will try to think about it tomorrow...

Testing different values for x in comparison using every pixel worked for some test scans - there were nearly the same results (primary color ratio, filled ratio).

(Would it be good to test a page perhaps several times and choose pixel randomly, to get a better result?)

import numpy as np
from pdf2image import convert_from_path
from PIL import Image
import time


def primary_color_ratio(pdf_name):
    """Return ratio of pixels that are the "background" color."""
    pages = convert_from_path(pdf_name, 300)
    bmp = pages[0].save("bmp.bmp", "BMP")
    image_rgb = np.array(Image.open("bmp.bmp").convert('RGB'))
    #examine just every xth pixel
    rgb = np.array(image_rgb).reshape(-1, 3)[::x]
    #get 24Bit Color
    b24 = rgb[:, 0] * 65536 + rgb[:, 1] * 256 + rgb[:, 2]
    _, counts = np.unique(b24, return_counts=True)
    return max(counts) / max(len(b24), 1)

#examine every xth pixel
x = 100
#"filled" is the content that can be read by humans (for example: writing)
#"userdef_image_filled_ratio_whole_page": the ratio at which an image is considered filled
userdef_image_filled_ratio_whole_page = 0.2
userdef_image_filled_ratio_x = userdef_image_filled_ratio_whole_page / x
pdf_name = "t2.pdf"
startTime = time.time()
primColorRatio = primary_color_ratio(pdf_name)
print("primColorRatio = " + str(primColorRatio))
filled_ratio = 1 - primColorRatio
endTime = time.time()
print("filled_ratio = " + str(filled_ratio))
print(endTime - startTime)
if filled_ratio >= userdef_image_filled_ratio_whole_page:
    print("The image is filled.")
else:
    print("The image is empty.")