I have images where I want to know the bit depth of the .bmp image. This is quite easy in windows manually (Properties>Details..) but there doesn't seem to much from google on it and the one answer I saw on here didn't (for me) show how to do it.
How to find the Bit Depth of an image
Code
import png as png
import numpy as np
r=png.Reader(filename = r'C:\Users\priper\Desktop\OPW_refac\grayscale.png')
a = r.read()
print(a[3]['bitdepth'])
or
from PIL import Image
import numpy as np
#Load the BMP file
img = Image.open(r'C:\Users\priper\Desktop\OPW_refac\HSS All As.bmp')
print(img, '\n')
print('bit depth :', img.mode)#this only tells me it is 8 pixels, I don't think it could tell me if it was 4.
#Or as a numpy array
img = np.array(Image.open(r'C:\Users\priper\Desktop\OPW_refac\HSS All As.bmp'))
print(img)
I can read the bit depth of a png but haven't a clue which library can get similar information so easily from a bmp.
You would probably be better off with a proper library, like wand or exiftool, but if you want something lightweight, this might be good enough - but I can't test it on your images as you haven't shared any:
#!/usr/bin/env python3
import sys
import struct
# Read first 100 bytes
with open('a.bmp','rb') as f:
BMP = f.read(100)
if BMP[0:2] != b'BM':
sys.exit('ERROR: Incorrect BMP signature')
# Get BITMAPINFOHEADER size - https://en.wikipedia.org/wiki/BMP_file_format
BITMAPINFOHEADERSIZE = struct.unpack('<i',BMP[14:18])[0]
okSizes = [40, 52, 56, 108, 124]
if BITMAPINFOHEADERSIZE not in okSizes:
sys.exit(f'ERROR: BITMAPINFOHEADER size was {BITMAPINFOHEADERSIZE}, expected one of {okSizes}')
# Get bits per pixel
bpp = struct.unpack('<H',BMP[28:30])[0]
print(f'bbp: {bpp}')
I created a sample BMP with ImageMagick like this:
magick -size 32x32 xc:red -define bmp:subtype=RGB565 a.bmp
I then ran my script and got bpp:16 matching exiftool output:
exiftool a.bmp
ExifTool Version Number : 12.00
File Name : a.bmp
Directory : .
File Size : 2.1 kB
File Modification Date/Time : 2021:02:24 12:01:51+00:00
File Access Date/Time : 2021:02:24 12:01:52+00:00
File Inode Change Date/Time : 2021:02:24 12:01:51+00:00
File Permissions : rw-r--r--
File Type : BMP
File Type Extension : bmp
MIME Type : image/bmp
BMP Version : Windows V5
Image Width : 32
Image Height : 32
Planes : 1
Bit Depth : 16 <--- HERE IT IS
Compression : Bitfields
Image Length : 2048
Pixels Per Meter X : 0
Pixels Per Meter Y : 0
Num Colors : Use BitDepth
Num Important Colors : All
Red Mask : 0x0000f800
Green Mask : 0x000007e0
Blue Mask : 0x0000001f
Alpha Mask : 0x00000000
Color Space : sRGB
Rendering Intent : Picture (LCS_GM_IMAGES)
Image Size : 32x32
Megapixels : 0.001
I then created a 24-bit BMP like this:
magick -size 32x32 xc:red a.bmp
and both my Python and exiftool report 24 bpp.
Keywords: Python. BMP, image processing, get depth, bit-depth, bpp.