[Libav-user] Colour space conversion

[Jasleen Kaur]

We have ARGB buffer to be compressed and then decoded also.
But for encoding the data the input as ARGB wasnt accepted.
The data was converted to YUV and then compressed, and on the receive side decoded and then converted back to ARGB.

The problem is that, While this conversion happens colours change.

Following is the code used to convert from ARGB to YUV and YUV to ARGB respectively.


void ConvertToYUV(int iWidth, int iHeight, BYTE* pARGBBuff)
{
#define RNDTO2(X) ( ( (X) & 0xFFFFFFFE )
#define RNDTO32(X) ( ( (X) % 32 ) ? ( ( (X) + 32 ) & 0xFFFFFFE0 ) : (X) )

//int ystride  = RNDTO32 ( iWidth );
    //int uvstride = RNDTO32 ( iWidth / 2 );
int ystride  = iWidth;
    int uvstride = iWidth / 2;
    int ysize    = ystride * iHeight;
    int vusize   = uvstride * ( iHeight / 2 );
    int size     = ysize + ( 2 * vusize );

if(m_sws_ctx == NULL)
{
//SwsFilter
m_sws_ctx = sws_getContext(iWidth,
iHeight,
AV_PIX_FMT_BGRA,
iWidth, iHeight,
AV_PIX_FMT_YUV420P,
SWS_FAST_BILINEAR, 0, 0, 0);

m_picture_buf = (uint8_t*)malloc(size);
}
    //uint8_t *plane[] = { m_picture_buf, m_picture_buf + ysize, m_picture_buf + ysize + vusize};
uint8_t *plane[] = { m_picture_buf, m_picture_buf + ysize + vusize, m_picture_buf + ysize};
    int stride[] = { ystride, uvstride, uvstride};

uint8_t *inData[1] = { pARGBBuff };
    int inLinesize[1] = { 4 * iWidth};

    sws_scale(m_sws_ctx, inData, inLinesize, 0, iHeight, plane, stride);
}

void ConvertToARGB(int iWidth, int iHeight)
{
#define RNDTO2(X) ( ( (X) & 0xFFFFFFFE )
#define RNDTO32(X) ( ( (X) % 32 ) ? ( ( (X) + 32 ) & 0xFFFFFFE0 ) : (X) )

int iSize = iWidth * iHeight * 4;
int ystride  = RNDTO32 ( iWidth );
    int uvstride = RNDTO32 ( iWidth / 2 );
    int ysize    = ystride * iHeight;
    int vusize   = uvstride * ( iHeight / 2 );


if(m_sws_ctx == NULL)
{
//SwsFilter
m_sws_ctx = sws_getContext(iWidth,
iHeight,
AV_PIX_FMT_YUV420P,
iWidth, iHeight,
AV_PIX_FMT_BGRA,
SWS_FAST_BILINEAR, 0, 0, 0);

m_picture_buf = (uint8_t*)malloc(iSize);
}
// src
int srcstride[] = {ystride, uvstride, uvstride};

// dest
uint8_t *destplane[] = {m_picture_buf};
    int stride[] = { iWidth * 4};
    int iHeightReturned = sws_scale(m_sws_ctx, m_picture->data, srcstride, 0, iHeight, destplane, stride);

  m_picture is the output of avcodec_decode_video2.
}


What correction needs to be done in the code, so that colours remain intact.

Thanks and regards
Jasleen
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