I'm a newbie developer and I need your help with something that is probably trivial for you.
I have an image data in this pixel format: 256 colors palettized RGBA. It comes from FFmpeg (PIX_FMT_PAL8) and it's explained this way:
PIX_FMT_RGB32 is handled in an endian-specific manner. An RGBA color is put together as:
(A << 24) | (R << 16) | (G << 8) | B
This is stored as BGRA on little-endian CPU architectures and ARGB on big-endian CPUs.
When the pixel format is palettized RGB (PIX_FMT_PAL8), the palettized image data is stored in AVFrame.data[0].
The palette is transported in AVFrame.data[1], is 1024 bytes long (256 4-byte entries) and is formatted the same as in PIX_FMT_RGB32 described above (i.e., it is also endian-specific). Note also that the individual RGB palette components stored in AVFrame.data[1] should be in the range 0..255.
AVFrame struct contains uint8_t *data[4] and int linesize[4] and they are described simply with:
uint8_t *data[4]= pointer to the picture planes- four components are given, that's all.
- the last component is alpha
int linesize[4]= number of bytes per line
I have the AVFrame struct with all the needed data but I don't know how to handle it. I need to create a NSImage from this image data.
How can I do this?
In case of a palettized image, the pixels contain a one byte value, which is an index into the palette. The palette has 256 entries.
Pixels are stored starting at address AVFrame.data[0]; the palette is stored starting at address AVFrame.data[1].
So to get the 4 bytes pixel value for the pixel at (X, Y), you can use first:
uint8_t Index= AVFrame.data[0][X + AVFrame.linesize[0] * Y];
to get the index into the palette, and then
int RGBA= ((int*)AVFrame.data[1])[Index];
to get the RGBA encoded value.