sws_scale, YUV to RGB conversion - c++

Question

I need convert YUV to RGB. I also need the RGB values to be in the limited range (16-235).
I try to use sws_scale function for this task.
My code you can see below. But after conversion I got the black pixel is (0, 0, 0) instead of (16, 16, 16).
Maybe there are some options to tell sws_scale function to calculate the limited range.
AVFrame* frameRGB = avFrameConvertPixelFormat(_decodedBuffer[i].pAVFrame, AV_PIX_FMT_RGB24);
AVFrame* Decoder::avFrameConvertPixelFormat(const AVFrame* src, AVPixelFormat dstFormat) {
int width = src->width;
int height = src->height;
AVFrame* dst = allocPicture(dstFormat, width, height);
SwsContext* conversion = sws_getContext(width,
height,
(AVPixelFormat)src->format,
width,
height,
dstFormat,
SWS_FAST_BILINEAR,
NULL,
NULL,
NULL);
sws_scale(conversion, src->data, src->linesize, 0, height, dst->data, dst->linesize);
sws_freeContext(conversion);
dst->format = dstFormat;
dst->width = src->width;
dst->height = src->height;
return dst;
}
Also I tried convert YUV pixel to RGB pixel manualy with formula and I got correct result. From YUV (16, 128, 128) I got (16, 16, 16) in RGB.
cmpR = y + 1.402 * (v - 128);
cmpG = y - 0.3441 * (u - 128) - 0.7141 * (v - 128);
cmpB = y + 1.772 * (u - 128);

Answer 1

You may the source format to "full scale" YUVJ.
As far as I know, sws_scale has no option for selecting Studio RGB as output format.
Changing the input format is the best solution I can think of.
The color conversion formula of "JPEG: YUV -> RGB" is the same as the formula in your post.
Examples for setting the source format:
If src->format is PIX_FMT_YUV420P, set the format to PIX_FMT_YUVJ420P.
If src->format is PIX_FMT_YUV422P, set the format to PIX_FMT_YUVJ422P.
If src->format is PIX_FMT_YUV444P, set the format to PIX_FMT_YUVJ444P.
If PIX_FMT_YUV440P, use PIX_FMT_YUVJ440P.
I know the solution is not covering all the possibilists, and there might be some output pixels exceeding the range of [16, 235], so it's not the most general solution...

Answer 2

yuv to rgb conversion using FFMPEG I see lot of information given already for this above. However for code completeness I am re-sharing the code with missing allocPicture() function, header & library to include, it works for me like a charm. Thanks to #Валентин Никин & #Rotem for most of the info & code.
Headers:
#include <libswscale/swscale.h>
Link FFMPEG Library:
libswscale
static AVFrame* allocPicture(enum AVPixelFormat pix_fmt, int width, int height)
{
// Allocate a frame
AVFrame* frame = av_frame_alloc();
if (frame == NULL)
{
fprintf(stderr, "avcodec_alloc_frame failed");
}
if (av_image_alloc(frame->data, frame->linesize, width, height, pix_fmt, 1) < 0)
{
fprintf(stderr, "av_image_alloc failed");
}
frame->width = width;
frame->height = height;
frame->format = pix_fmt;
return frame;
}
static AVFrame* avFrameConvertPixelFormat(const AVFrame* src, enum AVPixelFormat dstFormat)
{
int width = src->width;
int height = src->height;
AVFrame* dst = allocPicture(dstFormat, width, height);
struct SwsContext* conversion = sws_getContext(width,
height,
(enum AVPixelFormat)src->format,
width,
height,
dstFormat,
SWS_FAST_BILINEAR | SWS_FULL_CHR_H_INT | SWS_ACCURATE_RND,
NULL,
NULL,
NULL);
sws_scale(conversion, src->data, src->linesize, 0, height, dst->data, dst->linesize);
sws_freeContext(conversion);
dst->format = dstFormat;
dst->width = src->width;
dst->height = src->height;
return dst;
}
// convert yuv420p10le to rgb24 (or any other RGB formats)
AVFrame* frame = avFrameConvertPixelFormat(frame, AV_PIX_FMT_RGB24);