A small improvement, but using the TIFF compression option for screencapture is a bit quicker:
$ time screencapture -t png /tmp/test.png
real 0m0.235s
user 0m0.191s
sys 0m0.016s
$ time screencapture -t tiff /tmp/test.tiff
real 0m0.079s
user 0m0.028s
sys 0m0.026s
This does have a lot of overhead, as you say (the subprocess creation, writing/reading from disc, compressing/decompressing).
Instead, you could use PyObjC to capture the screen using CGWindowListCreateImage. I found it took about 70ms (~14fps) to capture a 1680x1050 pixel screen, and have the values accessible in memory
A few random notes:
- Importing the
Quartz.CoreGraphics module is the slowest part, about 1 second. Same is true for importing most of the PyObjC modules. Unlikely to matter in this case, but for short-lived processes you might be better writing the tool in ObjC
- Specifying a smaller region is a bit quicker, but not hugely (~40ms for a 100x100px block, ~70ms for 1680x1050). Most of the time seems to be spent in just the
CGDataProviderCopyData call - I wonder if there's a way to access the data directly, since we dont need to modify it?
- The
ScreenPixel.pixel function is pretty quick, but accessing large numbers of pixels is still slow (since 0.01ms * 1650*1050 is about 17 seconds) - if you need to access lots of pixels, probably quicker to struct.unpack_from them all in one go.
Here's the code:
import time
import struct
import Quartz.CoreGraphics as CG
class ScreenPixel(object):
"""Captures the screen using CoreGraphics, and provides access to
the pixel values.
"""
def capture(self, region = None):
"""region should be a CGRect, something like:
>>> import Quartz.CoreGraphics as CG
>>> region = CG.CGRectMake(0, 0, 100, 100)
>>> sp = ScreenPixel()
>>> sp.capture(region=region)
The default region is CG.CGRectInfinite (captures the full screen)
"""
if region is None:
region = CG.CGRectInfinite
else:
# TODO: Odd widths cause the image to warp. This is likely
# caused by offset calculation in ScreenPixel.pixel, and
# could could modified to allow odd-widths
if region.size.width % 2 > 0:
emsg = "Capture region width should be even (was %s)" % (
region.size.width)
raise ValueError(emsg)
# Create screenshot as CGImage
image = CG.CGWindowListCreateImage(
region,
CG.kCGWindowListOptionOnScreenOnly,
CG.kCGNullWindowID,
CG.kCGWindowImageDefault)
# Intermediate step, get pixel data as CGDataProvider
prov = CG.CGImageGetDataProvider(image)
# Copy data out of CGDataProvider, becomes string of bytes
self._data = CG.CGDataProviderCopyData(prov)
# Get width/height of image
self.width = CG.CGImageGetWidth(image)
self.height = CG.CGImageGetHeight(image)
def pixel(self, x, y):
"""Get pixel value at given (x,y) screen coordinates
Must call capture first.
"""
# Pixel data is unsigned char (8bit unsigned integer),
# and there are for (blue,green,red,alpha)
data_format = "BBBB"
# Calculate offset, based on
# http://www.markj.net/iphone-uiimage-pixel-color/
offset = 4 * ((self.width*int(round(y))) + int(round(x)))
# Unpack data from string into Python'y integers
b, g, r, a = struct.unpack_from(data_format, self._data, offset=offset)
# Return BGRA as RGBA
return (r, g, b, a)
if __name__ == '__main__':
# Timer helper-function
import contextlib
@contextlib.contextmanager
def timer(msg):
start = time.time()
yield
end = time.time()
print "%s: %.02fms" % (msg, (end-start)*1000)
# Example usage
sp = ScreenPixel()
with timer("Capture"):
# Take screenshot (takes about 70ms for me)
sp.capture()
with timer("Query"):
# Get pixel value (takes about 0.01ms)
print sp.width, sp.height
print sp.pixel(0, 0)
# To verify screen-cap code is correct, save all pixels to PNG,
# using http://the.taoofmac.com/space/projects/PNGCanvas
from pngcanvas import PNGCanvas
c = PNGCanvas(sp.width, sp.height)
for x in range(sp.width):
for y in range(sp.height):
c.point(x, y, color = sp.pixel(x, y))
with open("test.png", "wb") as f:
f.write(c.dump())
autopy.color.hex_to_rgb(autopy.screen.get_color(1, 1))? – Mariahmariam