PremultiplyAlpha

This converts an image assuming the original is not using premultiplied alpha into a premultiplied alpha version of the same image. The format and size are not changed.

Breaking Change notice: The 'flags' parameter was not present in the August 2013 and previous versions of DirectXTex.

HRESULT PremultiplyAlpha( const Image& srcImage, DWORD flags,
    ScratchImage& image );

HRESULT PremultiplyAlpha( const Image* srcImages, size_t nimages,
    const TexMetadata& metadata, DWORD flags,
    ScratchImage& result );

Parameters

flags: Combination of options to apply

PMALPHA_IGNORE_SRGB Ignore any sRGB colorspace conversions

This controls color space transformation for conversions.

TEX_PMALPHA_SRGB_IN Indicates the input format is the sRGB format. This is implied if using a DXGI_FORMAT_*_SRGB format
TEX_PMALPHA_SRGB_OUT Indicates the output format is the sRGB format. This is implied if using a DXGI_FORMAT_*_SRGB format
TEX_PMALPHA_SRGB This is the same as setting both TEX_PMALPHA_SRGB_IN and TEX_PMALPHA_SRGB_OUT

Example

ScratchImage srcImage;

...

ScratchImage destImage;
hr = PremultiplyAlpha( srcImage.GetImages(), srcImage.GetImageCount(), srcImage.GetMetadata(), TEX_PMALPHA_DEFAULT destImage );
if ( FAILED(hr) )
    ...

Remarks

This function does not operate directly on block compressed images. See Decompress and Compress.

This function cannot operate directly on a planar format image. See ConvertToSinglePlane for a method for converting planar data to a format that is supported by this routine.

This is most useful for working with rendering that relies on premultiplied alpha blending (see DirectXTK).