rgb order

[Pawel Veselov]

Hi.

Sorry if this sounds stupid, I don't do image/video a lot.

What should I expect the order of a/r/g/b components after *ToARGB() conversion?

I'm converting YUYV(YUY2) to ARGB. YUY2 comes from a webcam (v4l2 drivers), 

and is advertised as YUYV.

When I draw the ARGB using GDK, which expects red, green, blue, padding bytes

(using gdk_draw_rgb_32_image() and I don't care about alpha), red and blue components

are clearly switched around. Same if I do ARGBToRGB24, and use gdk_draw_rgb_image,

which expects red, green and blue bytes. 

Is there a good resource on understanding the order of components for these various 

*RGB formats, and whether they are supposed to be treated as byte arrays, or wider

types, which would make host byte order matter.

Thank you.

[Frank Barchard]

Hi Pawel,

Its not a stupid question at all... channel ordering is a common area of confusion.

For 32 bit ARGB formats, the ordering refers to the order in a register.  On a little endian machine the order in memory will be the opposite.

This documentation is supposed to cover that, but if its unclear or incomplete, let me know.

https://code.google.com/p/libyuv/wiki/Formats

The fourcc convention comes mainly from fourcc.org which is Windows centric.  The video_common.h has a few links/info as well.

For your particular questions

RGBx in memory would be FOURCC_ABGR

For 24 bit R,G,B in memory it would be FOURCC_RAW

And the function names follow the same naming conventions.

There is no direct conversion from YUY2ToABGR or RAW - it would take 2 steps.

YUY2ToI420 and I420ToABGR.  Or YUY2ToARGB and ARGBToABGR.

The later would be easier to code - you could do the 2nd step in place and RGB formats only need one buffer/pointer.  But 32 bit is more memory so likely a bit slower.

If you think a direct conversion would be important, open an 'issue'

https://code.google.com/p/libyuv/issues/list

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[Pawel Veselov]

Hi Frank,

the Wiki page really helps with ARGB fourccs, thank you.

I am doing the conversion in two steps: YUY2ToARGB then ARGBToRGB24 (RGB24 is same as raw, right?).

raw should be, byte-to-byte, R,G,B (if I understood you correctly about FOURCC_RAW), so I shouldn't see R/B channels swapped...

[Frank Barchard]

FOURCC_RAW is R,G,B in memory.

FOURCC_RGB24 is B,G,R in memory.