[M4IF Technotes] ´ð¸´: [M4IF Technotes] layout of YUV files

[lmwang]

Dear Stefan,
Below is my routine to your topic, only yuv420 to rgb24 involved in.
pieces of code for easy understanding. I can't sure whether it works,
you can test it.
/* 
 * pDst: pointer to RGB 
 * pY,pU,pV: pointer to Y,U,V data
  * image_width,image_height,image stride: Y planar width,height,stride.
*/
int yuv2rgb_24(uint8_t* pDst,uint8_t pY, uint8_t pU, uint8_t pV, int
image_width,int int image_height,int image_stide)
{
	uint8_t Y0,Y1,Y2,Y3;
	uint8_t U,V;
	int i,j;
	for( i = 0; i < image_height/2; i++)
		for(j = 0; j < image_width/2; j++)
		{
			Y0 = pY[2*j*image_stride + 2*i];
			Y1 = pY[2*j*image_stide + 2*i+1];
			Y2 = pY[2*(j+1)*image_stride + 2*i] // the
second line
			Y3 = pY[2*(j+1)*image_stride + 2*i+1] // the
second line
			U = pU[j*image_stride/2+ i];
			V = pV[j*image_stride/2 +i]
			pDst[2*j*image_stride*3+12i] = alpha00*Y0 +
alpha01*U+alpha02*V;
pDst[2*j*image_stride*3+12i+1]=alpha10*Y0+alpha11*U+alpha12*V;
pDst[2*j*image_stride*3+12i_2]=alpha20*Y0+alpha21*U+alpha22*V;
			....
		}
}			
If you don't mind, you can post the whole test routine.
Best Regards,
Limin
-----????-----
???: technotes-admin   lists.m4if.org
[mailto:technotes-admin   lists.m4if.org] ?? Stefan A. Goor
????: 2003?4?20? 0:52
???: M4IF
??: [M4IF Technotes] layout of YUV files
Hi Everyone,
I have a problem that's been baffling me for a few days.
I'm trying read the YUV reference clips such as akiyo_qcif.yuv etc in
terms
of Y U and V components (or more accuractely Y Cr Cb, so I'm told) and
convert them to RGB format.  I know there are tools available to do this
but
I am specifically coding in java and would like to be able to control
exactly what is going on in terms of pixels.
Basically the problem occurs when I do the conversion.  My understanding
is
that these files are planar YUV format (i.e. YYYYYYY....UUUU....VVVV)
and
not interlaced (i.e. YUYVYU...... etc).  Taking into account that all
the
frames are QCIF, the format is 4:2:0 and each Y U or V component is 1
byte,
I assume that reading the first 25344 (176x144) bytes is the Y
component,
the next 6776 (88x77) bytes are U and the next 6776 bytes are the V
component and so on and so forth for each frame.
I separated the components out into individual files and used Paintshop
to
display these as raw greyscale images and it seems to coincide with what
I
understood but as you can see from the pictures on
http://www.netsoc.ucd.ie/~stefg/Qs/Question.html.  The U and V files are
the
same size as the Y component because I scaled them up a factor of 4 to
convert them to QCIF size i.e.
a b ..   =		a a b b ..
c d ..		a a b b ..
. .			c c d d ..
. .			c c d d ..
			. . . .
			. . . .
Having this data, I tried to convert it to RGB using the following
equations
that I found on many websites so I'm guessing they're correct:
int R_value = (int)((1.164 * (Y_value - 16)) + (1.596 * (V_value -
128)));
int G_value = (int)((1.164 * (Y_value - 16)) - (0.813 * (V_value - 128))
-
(0.391 * (U_value - 128)));
int B_value = (int)((1.164 * (Y_value - 16)) + (2.018 * (U_value -
128)));
and after each conversion any errors must be corrected using code such
as:
if(value<0)
	value = 0;
else if (value>255)
	value = 255;
But as you can the result
(http://www.netsoc.ucd.ie/~stefg/Qs/Question.html)
that I got from the conversion was just random garbage.
As a result, I'm wondering is yuv data layed out in files with the first
byte representing the top left corner pixel and the next byte the next
pixel
to the right etc?
Does any one have any ideas, what went wrong? Are any of my assumption
wrong?
Sorry about the long-winded email, but I just wanted to state the
problem
clearly,
Thanks for you help,
Stefan
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