Contents

vImageInterpolatedLookupTable_PlanarF(_:_:_:_:_:_:_:)

Uses an interpolated lookup table to transform a 32-bit planar image.

Declaration

func vImageInterpolatedLookupTable_PlanarF(_ src: UnsafePointer<vImage_Buffer>, _ dest: UnsafePointer<vImage_Buffer>, _ table: UnsafePointer<Pixel_F>, _ tableEntries: vImagePixelCount, _ maxFloat: Float, _ minFloat: Float, _ flags: vImage_Flags) -> vImage_Error

Parameters

  • 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.

  • table:

    A lookup table that contains Pixel_f values.

  • tableEntries:

    The number of values in the lookup table.

  • maxFloat:

    A value of type float.

  • minFloat:

    A value of type float.

  • flags:

    The options to use when performing the operation. If your code implements its own tiling or its own multithreading, pass Kvimagedonottile.

Return Value

kvImageNoError; otherwise, one of the error codes in Data Types and Constants.

Discussion

Provide this function with a lookup table with any number of values, but with a minimum value of minFloat and a maximum value of maxFloat. The function generates lookup values by linearly interpolating between the supplied values. The per-pixel conversion calculation is equivalent to the following:

float clippedPixel = MAX( MIN( src_pixel, maxFloat ), minFloat );    //clip src_pixel to be in range
float fIndex = (float) (tableEntries - 1) * (clippedPixel - minFloat ) / (maxFloat - minFloat);
float fract = fIndex - floor( fIndex );
unsigned long index =  fIndex;
float result = table[ index ] * ( 1.0f - fract ) + table[ index + 1] * fract;

The following code shows a lookup table that contains two values, 1 and 0. The result is that the lookup transformation maps the source values 0...1 to the destination values 1...0.

let lookupTable: [Float] = [1, 0]

let source = vImage.PixelBuffer<vImage.PlanarF>(
    pixelValues: [0.2, 0.4, 0.6, 0.8],
    size: .init(width: 4, height: 1))

let destination = vImage.PixelBuffer<vImage.PlanarF>(
    size: source.size)

source.withUnsafePointerToVImageBuffer{ src in
    destination.withUnsafePointerToVImageBuffer { dest in
        
        _ = vImageInterpolatedLookupTable_PlanarF(
            src,
            dest,
            lookupTable,
            vImagePixelCount(lookupTable.count),
            1, 0,
            vImage_Flags(kvImageNoFlags))
    }
}

// Prints "[0.8, 0.6, 0.4, 0.2]".
print(destination.array)

See Also

Transforming planar-to-planar with a lookup table