FreeImage wrong image color - c++

Question

I am trying to extract frames from a stream which I create with Gstreamer and trying to save them with FreeImage or QImage ( this one is for testing ).
GstMapInfo bufferInfo;
GstBuffer *sampleBuffer;
GstStructure *capsStruct;
GstSample *sample;
GstCaps *caps;
int width, height;
const int BitsPP = 32;
/* Retrieve the buffer */
g_signal_emit_by_name (sink, "pull-sample", &sample);
if (sample) {
sampleBuffer = gst_sample_get_buffer(sample);
gst_buffer_map(sampleBuffer,&bufferInfo,GST_MAP_READ);
if (!bufferInfo.data) {
g_printerr("Warning: could not map GStreamer buffer!\n");
throw;
}
caps = gst_sample_get_caps(sample);
capsStruct= gst_caps_get_structure(caps,0);
gst_structure_get_int(capsStruct,"width",&width);
gst_structure_get_int(capsStruct,"height",&height);
auto bitmap = FreeImage_Allocate(width, height, BitsPP,0,0,0);
memcpy( FreeImage_GetBits( bitmap ), bufferInfo.data, width * height * (BitsPP/8));
// int pitch = ((((BitsPP * width) + 31) / 32) * 4);
// auto bitmap = FreeImage_ConvertFromRawBits(bufferInfo.data,width,height,pitch,BitsPP,0, 0, 0);
FreeImage_FlipHorizontal(bitmap);
bitmap = FreeImage_RotateClassic(bitmap,180);
static int id = 0;
std::string name = "/home/stadmin/pic/sample" + std::to_string(id++) + ".png";
#ifdef FREE_SAVE
FreeImage_Save(FIF_PNG,bitmap,name.c_str());
#endif
#ifdef QT_SAVE
//Format_ARGB32
QImage image(bufferInfo.data,width,height,QImage::Format_ARGB32);
image.save(QString::fromStdString(name));
#endif
fibPipeline.push(bitmap);
gst_sample_unref(sample);
gst_buffer_unmap(sampleBuffer, &bufferInfo);
return GST_FLOW_OK;
The color output in FreeImage are totally wrong like when Qt - Format_ARGB32 [ greens like blue or blues like oranges etc.. ] but when I test with Qt - Format_RGBA8888 I can get correct output. I need to use FreeImage and I wish to learn how to correct this.

Answer 1

Since you say Qt succeeds using Format_RGBA8888, I can only guess: the gstreamer frame has bytes in RGBA order while FreeImage expects ARGB.
Quick fix:
//have a buffer the same length of the incoming bytes
size_t length = width * height * (BitsPP/8);
BYTE * bytes = (BYTE *) malloc(length);
//copy the incoming bytes to it, in the right order:
int index = 0;
while(index < length)
{
bytes[index] = bufferInfo.data[index + 2]; //B
bytes[index + 1] = bufferInfo.data[index + 1]; //G
bytes[index + 2] = bufferInfo.data[index]; //R
bytes[index + 3] = bufferInfo.data[index + 3]; //A
index += 4;
}
//fill the bitmap using the buffer
auto bitmap = FreeImage_Allocate(width, height, BitsPP,0,0,0);
memcpy( FreeImage_GetBits( bitmap ), bytes, length);
//don't forget to
free(bytes);