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Discrete transfer effect

Use the discrete transfer effect to map the color intensities of an image using a step transfer function created from a list of values you provide.

The CLSID for this effect is CLSID_D2D1DiscreteTransfer.

Example image

The image here shows the input and output of the discrete transfer effect.

Before
After

```
ComPtr<ID2D1Effect> discreteTransferEffect;
m_d2dContext->CreateEffect(CLSID_D2D1DiscreteTransfer, &discreteTransferEffect);

discreteTransferEffect->SetInput(0, bitmap);

float table[2] = {0.0f, 0.5f, 1.0f};
discreteTransferEffect->SetValue(D2D1_DISCRETETRANSFER_PROP_RED_TABLE, table);
discreteTransferEffect->SetValue(D2D1_DISCRETETRANSFER_PROP_GREEN_TABLE, table);
discreteTransferEffect->SetValue(D2D1_DISCRETETRANSFER_PROP_BLUE_TABLE, table);

m_d2dContext->BeginDraw();
m_d2dContext->DrawImage(discreteTransferEffect.Get());
m_d2dContext->EndDraw();

```

The transfer function is based on the list of inputs: V=(V0,V1,V2,V3,Vk…,VN) where N is the number of elements - 1.

The input pixel intensity is represented as C. The output pixel intensity, C‘ is calculated with the equation:

For a value C, pick a value k, such that:

The output C’ can be calculated using the equation: C' = Vk

This effect works on straight and premultiplied alpha images. The effect outputs premultiplied alpha bitmaps.

Here is what the graph of discrete transfer function looks like if the inputs are `[0.25, 0.5, 0.75, 1.0]`.

Effect properties

Note  The values of all channels of the discrete transfer properties are unitless and have a minimum of 0.0 and a maximum 1.0.

Display name and index enumerationType and default valueDescription

RedTable

D2D1_DISCRETETRANSFER_PROP_RED_TABLE

FLOAT[]

{0.0f, 1.0f}

The list of values used to define the transfer function for the Red channel.

RedDisable

D2D1_DISCRETETRANSFER_PROP_RED_DISABLE

BOOL

FALSE

If you set this to TRUE the effect does not apply the transfer function to the Red channel. If you set this to FALSE the effect applies the RedDiscreteTransfer function to the Red channel.

GreenTable

D2D1_DISCRETETRANSFER_PROP_GREEN_TABLE

FLOAT[]

{0.0f, 1.0f}

The list of values that define the transfer function for the Green channel.

GreenDisable

D2D1_DISCRETETRANSFER_PROP_GREEN_DISABLE

BOOL

FALSE

If you set this to TRUE the effect does not apply the transfer function to the Green channel. If you set this to FALSE the effect applies the GreenDiscreteTransfer function to the Green channel.

BlueTable

D2D1_DISCRETETRANSFER_PROP_BLUE_TABLE

FLOAT[]

{0.0f, 1.0f}

The list of values that define the transfer function for the Blue channel.

BlueDisable

D2D1_DISCRETETRANSFER_PROP_BLUE_DISABLE

BOOL

FALSE

If you set this to TRUE the effect does not apply the transfer function to the Blue channel. If you set this to FALSE the effect applies the BlueDiscreteTransfer function to the Blue channel.

AlphaTable

D2D1_DISCRETETRANSFER_PROP_ALPHA_TABLE

FLOAT[]

{0.0f, 1.0f}

The list of values that define the transfer function for the Alpha channel.

D2D1_DISCRETETRANSFER_PROP_ALPHA_DISABLE

BOOL

FALSE

If you set this to TRUE the effect does not apply the transfer function to the Alpha channel. If you set this to FALSE the effect applies the AlphaDiscreteTransfer function to the Alpha channel.

ClampOutput

D2D1_DISCRETETRANSFER_PROP_CLAMP_OUTPUT

BOOL

FALSE

Whether the effect clamps color values to between 0 and 1 before the effect passes the values to the next effect in the graph. The effect clamps the values before it premultiplies the alpha.

If you set this to TRUE the effect will clamp the values. If you set this to FALSE, the effect will not clamp the color values, but other effects and the output surface may clamp the values if they are not of high enough precision.