I have a screenshot in my clipboard.
I have used win32clipboard.GetClipboardData(win32con.CF_DIB) to get a string, and written the string to a .bmp file, but it could not be opened by a picture viewer.
So, without PIL (and other image third part libs), how to write the image in clipboard to local?
The primary problem with your simple approach is that the string written to the file is missing a .bmp file header, which is a BITMAPFILEHEADER structure.
In order to create the file header at least some of the information in the string returned by the GetClipboardData() call must be decoded. For CF_DIB clipboard format, the first part of the data in the string will be a BITMAPINFOHEADER.
This header structure is a very general as there are many different flavors of DIBs with various bits-per-component and kinds-of-compression. Fortunately the one used for screenshots is very simple — uncompressed RGBA pixels.
That fact makes things much easier because otherwise determining the value to put in the bfOffBits field of the BITMAPFILEHEADER would be complicated by the fact that in most other cases there's also a variably-sized color table following the BITMAPINFOHEADER and the start of the pixel array.
Below is example code that handles that case (only):
import ctypes
from ctypes.wintypes import *
import win32clipboard
from win32con import *
import sys
class BITMAPFILEHEADER(ctypes.Structure):
_pack_ = 1 # structure field byte alignment
_fields_ = [
('bfType', WORD), # file type ("BM")
('bfSize', DWORD), # file size in bytes
('bfReserved1', WORD), # must be zero
('bfReserved2', WORD), # must be zero
('bfOffBits', DWORD), # byte offset to the pixel array
]
SIZEOF_BITMAPFILEHEADER = ctypes.sizeof(BITMAPFILEHEADER)
class BITMAPINFOHEADER(ctypes.Structure):
_pack_ = 1 # structure field byte alignment
_fields_ = [
('biSize', DWORD),
('biWidth', LONG),
('biHeight', LONG),
('biPLanes', WORD),
('biBitCount', WORD),
('biCompression', DWORD),
('biSizeImage', DWORD),
('biXPelsPerMeter', LONG),
('biYPelsPerMeter', LONG),
('biClrUsed', DWORD),
('biClrImportant', DWORD)
]
SIZEOF_BITMAPINFOHEADER = ctypes.sizeof(BITMAPINFOHEADER)
win32clipboard.OpenClipboard()
try:
if win32clipboard.IsClipboardFormatAvailable(win32clipboard.CF_DIB):
data = win32clipboard.GetClipboardData(win32clipboard.CF_DIB)
else:
print('clipboard does not contain an image in DIB format')
sys.exit(1)
finally:
win32clipboard.CloseClipboard()
bmih = BITMAPINFOHEADER()
ctypes.memmove(ctypes.pointer(bmih), data, SIZEOF_BITMAPINFOHEADER)
if bmih.biCompression != BI_BITFIELDS: # RGBA?
print('insupported compression type {}'.format(bmih.biCompression))
sys.exit(1)
bmfh = BITMAPFILEHEADER()
ctypes.memset(ctypes.pointer(bmfh), 0, SIZEOF_BITMAPFILEHEADER) # zero structure
bmfh.bfType = ord('B') | (ord('M') << 8)
bmfh.bfSize = SIZEOF_BITMAPFILEHEADER + len(data) # file size
SIZEOF_COLORTABLE = 0
bmfh.bfOffBits = SIZEOF_BITMAPFILEHEADER + SIZEOF_BITMAPINFOHEADER + SIZEOF_COLORTABLE
bmp_filename = 'clipboard.bmp'
with open(bmp_filename, 'wb') as bmp_file:
bmp_file.write(bmfh)
bmp_file.write(data)
print('file "{}" created from clipboard image'.format(bmp_filename))
