I420toRGB

Versioned name: I420toRGB-8

Category: Image processing

Short description: I420toRGB performs image conversion from I420 to RGB format.

Detailed description:

Conversion of each pixel from I420 (YUV) to RGB space is represented by the following formulas (same as in NV12toRGB):

\[\begin{split}\begin{aligned} & R = 1.164 \cdot (Y - 16) + 1.596 \cdot (V - 128) \\ & G = 1.164 \cdot (Y - 16) - 0.813 \cdot (V - 128) - 0.391 \cdot (U - 128) \\ & B = 1.164 \cdot (Y - 16) + 2.018 \cdot (U - 128) \end{aligned}\end{split}\]

Then R, G, B values are clipped to range (0, 255).

Inputs:

Input I420 image tensor shall have NHWC (also known as NYXC) layout and can be represented in two ways:

  • Single plane:

    • 1: Tensor of type T. Required. Dimensions:

      • N - batch dimension

      • H - height dimension is 1.5x bigger than the image height

      • W - width dimension is the same as the image width

      • C - channels dimension is equal to 1 (one plane)

  • Three separate planes - Y, U and V:

    • 1: Tensor of type T representing Y plane. Required. Dimensions:

      • N - batch dimension

      • H - height dimension is the same as the image height

      • W - width dimension is the same as the image width

      • C - channels dimension is equal to 1 (only Y channel)

    • 2: Tensor of type T representing U plane. Required. Dimensions:

      • N - batch dimension. Shall be the same as the batch dimension for Y plane

      • H - height dimension shall be half of the image height (for example, image_height / 2)

      • W - width dimension shall be half of the image width (for example, image_width / 2)

      • C - channels dimension shall be equal to 1 (U channel)

    • 3: Tensor of type T representing V plane. Required. Dimensions:

      • N - batch dimension. Shall be the same as the batch dimension for Y plane

      • H - height dimension shall be half of the image height (for example, image_height / 2)

      • W - width dimension shall be half of the image width (for example, image_width / 2)

      • C - channels dimension shall be equal to 1 (V channel)

Outputs:

  • 1: A tensor of type T representing an image converted in RGB format. Dimensions:

    • N - batch dimension

    • H - height dimension is the same as the image height

    • W - width dimension is the same as the image width

    • C - channels dimension is equal to 3. The first channel is Red, the second one is Green, the last one is Blue

Types:

  • T: uint8 or any supported floating-point type.

Examples:

Example 1

<layer ... type="I420toRGB">
    <input>
        <port id="0">
            <dim>1</dim>
            <dim>720</dim>
            <dim>640</dim>
            <dim>1</dim>
        </port>
    </input>
    <output>
        <port id="1">
            <dim>1</dim>
            <dim>480</dim>
            <dim>640</dim>
            <dim>3</dim>
        </port>
    </output>
</layer>

Example 2

<layer ... type="I420toRGB">
    <input>
        <port id="0">  <!-- Y plane -->
            <dim>1</dim>
            <dim>480</dim>
            <dim>640</dim>
            <dim>1</dim>
        </port>
        <port id="1">  <!-- U plane -->
            <dim>1</dim>
            <dim>240</dim>
            <dim>320</dim>
            <dim>1</dim>
        </port>
        <port id="2">  <!-- V plane -->
          <dim>1</dim>
          <dim>240</dim>
          <dim>320</dim>
          <dim>1</dim>
        </port>
    </input>
    <output>
        <port id="1">
            <dim>1</dim>
            <dim>480</dim>
            <dim>640</dim>
            <dim>3</dim>
        </port>
    </output>
</layer>