vImageConvert_RGBA8888toRGBA5551(_:_:_:)
Converts an 8-bit-per-channel, 4-channel interleaved buffer to an RGBA5551 4-channel interleaved buffer.
Declaration
func vImageConvert_RGBA8888toRGBA5551(_ src: UnsafePointer<vImage_Buffer>, _ dest: UnsafePointer<vImage_Buffer>, _ flags: vImage_Flags) -> vImage_ErrorParameters
- src:
The source vImage buffer.
- dest:
A pointer to the destination vImage buffer structure. You’re responsible for filling out the Height, Width, and Rowbytes fields of this structure, and for allocating a data buffer of the appropriate size. On return, the data buffer this structure points to contains the destination image data. When you no longer need the data buffer, deallocate the memory to prevent memory leaks.
- flags:
The options to use when performing the operation. If your code implements its own tiling or its own multithreading, pass Kvimagedonottile; otherwise, pass Kvimagenoflags.
Return Value
kvImageNoError; otherwise, one of the error codes in Data Types and Constants.
Discussion
The RGBA5551 format has 16-bit pixels with 1 bit for alpha and 5 bits each for red, green, and blue. The function uses the following calculation to perform the conversion:
uint32_t red = (8bitRedChannel * 31 + 127) / 255;
uint32_t green = (8bitGreenChannel * 31 + 127) / 255;
uint32_t blue = (8bitBlueChannel * 31 + 127) / 255;
uint32_t alpha = (8bitAlphaChannel + 127) / 255;
dest->data[x] = (red << 11) | (green << 6) | (blue << 1) | alpha;