Re: [pygame] BGRA to RGB/RGBA, fastest way to do so

[Silver <rockachu2@xxxxxxxxx>]

On 9/1/2012 12:52 PM, gm770 wrote:
> I'm trying to convert a color string buffer, and looking for the fastest way
> to do so.
> I'm capturing a 2 screen desktop (h=1080, w=3840), but it comes in as BGRA,
> and I don't see an obvious way to convert that to RGBA or RGB.
> 
> The fastest way I have so far is ~1.78 sec, but I'm sure there must be
> something faster.
> 
> def toRGBA(BGRA_str):
>         buf = bytearray(BGRA_str)
>         for x in xrange(0,len(buf),4):
>                 buf[x], buf[x+2] = buf[x+2], buf[x]
>         return buf
> 
> Slower methods include: 
> - starting with an empty array, and via loop, appending to create RGB. (~3.8
> sec)
> - turn the buffer to a list of chars, swap and return the joined results.
> (~2.14 sec)
> 
> 
> 
> --
> View this message in context: http://pygame-users.25799.n6.nabble.com/BGRA-to-RGB-RGBA-fastest-way-to-do-so-tp163.html
> Sent from the pygame-users mailing list archive at Nabble.com.
> 
From the doc page comments:
As for "BGR" (OpenCV): Just use "RBG" but reverse the string first
and then flip the surface (vertically and horizontally).

I am using this with fromstring:

frame = cvQueryFrame(capture)                    # get a video frame
using OpenCV
bgr = frame.imageData                            # this is a string
using BGR
rgb = bgr[::-1]                                  # reverse it to get RGB
im = pygame.image.fromstring(rgb, size, 'RGB')   # create pygame surface
im = pygame.transform.flip(im, True, True)       # flip it



you could also use map():

x = [buf[x], buf[x+2] for x in xrange(0, len(buf), 4)]## convert to list
format

map(lambda x: [x[2], x[1], x[0], x[3]], bgra) ## returns a list of
four-item lists in RGBA format.


or you could import/export it from pygame:

ARGB = BGRA[::-1]
ARGB_image = pygame.image.fromstring(ARGB, size, "ARGB")
RGBA_str = pygame.image.tostring(ARGB_image, "RGBA")