sws_scale YUV --> RGB distorted image

Question

I want to convert YUV420P image (received from H.264 stream) to RGB, while also resizing it, using sws_scale.
The size of the original image is 480 × 800. Just converting with same dimensions works fine.
But when I try to change the dimensions, I get a distorted image, with the following pattern:

changing to 481 × 800 will yield a distorted B&W image which looks like it's cut in the middle
482 × 800 will be even more distorted
483 × 800 is distorted but in color
484 × 800 is ok (scaled correctly).

Now this pattern follows - scaling will only work fine if the difference between divides by 4.

Here's a sample code of the way that I decode and convert the image. All methods show "success".

int srcX = 480;
int srcY = 800;
int dstX = 481; // or 482, 483 etc
int dstY = 800;

AVFrame* avFrameYUV = avcodec_alloc_frame();
avpicture_fill((AVPicture *)avFrameYUV, decoded_yuv_frame, PIX_FMT_YUV420P, srcX , srcY);

AVFrame *avFrameRGB = avcodec_alloc_frame();

AVPacket avPacket;
av_init_packet(&avPacket);
avPacket.size = read; // size of raw data
avPacket.data = raw_data; // raw data before decoding to YUV

int frame_decoded = 0;
int decoded_length = avcodec_decode_video2(g_avCodecContext, avFrameYUV, &frame_decoded, &avPacket);
int size = dstX * dstY * 3;

struct SwsContext *img_convert_ctx = sws_getContext(srcX, srcY, SOURCE_FORMAT, dstX, dstY, PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);

avpicture_fill((AVPicture *)avFrameRGB, rgb_frame, PIX_FMT_RGB24, dstX, dstY);
sws_scale(img_convert_ctx, avFrameYUV->data, avFrameYUV->linesize, 0, srcY, avFrameRGB->data, avFrameRGB->linesize);

// draws the resulting frame with windows BitBlt
DrawBitmap(hdc, dstX, dstY, rgb_frame, size);

sws_freeContext(img_convert_ctx);

In sws_getContext() function you are passing as parameter the format identifier PIX_FMT_BGR24 instead of PIX_FMT_RGB24 as you do in avpicture_fill — Didac Perez Parera

Yoon Chang Kook Yoon Chang Kook · Accepted Answer · 2013-11-19T08:45:30

When you make a bitmap image, the width of image MUST be multiple of 4.

So you have to change width like 480, 484, 488, 492 ...

Here is method to change to multiple of 4

#define WIDTHBYTES(bits) (((bits) + 31) / 32 * 4)

void main()
{
    BITMAPFILEHEADER bmFileHeader;
    BITMAPINFOHEADER bmInfoHeader;

    // load image
    // ...

    // when you use the method, put parameter like this.
    int tempWidth = WIDTHBYTES(width * bmInfoHeader.biBitCount);
}

I hope you solve the problem.

sws_scale YUV --> RGB distorted image

1 Answers