## Operator CastKernel

Operator Library: Base

With the CastKernel operator, you can re-organize the parallelism and kernel size of the incoming data. For re-interpretation, change the kernel size at the output link. For example, an input link is configured with two kernel rows and two kernel columns and a parallelism of four. The CastKernel operator gives you the possibility to interpret these as four kernel rows and four kernel columns at parallelism 1 or as one kernel row and two kernel columns at parallelism 8, etc. The constraint of the CastKernel operator is that the product of kernel row and kernel column and parallelism must be identical for the input and the output link.

The following examples illustrate the conversion of kernel configuration and parallelism performed by the operator. The pseudo-code below the illustrations also describes the conversion pattern.

Example 1: Converting the kernel size (col x row) 3x1 to the kernel size 1x3 while keeping parallelism 2:

Example 2: Converting parallelism 2 and kernel size (col x row) 2x3 to parallelism 3 and kernel size 2x2:

Example 3: Converting parallelism 1 and kernel size (col x row) 3x2 to parallelism 6 and kernel size 1x1:

The operator changes the width of the images.

The mapping follows the following pseudo-code:

```
pi = 0
ri = 0
ci = 0
for p in 0 to P-1
for r in 0 to R-1
for c in 0 to C-1
O[p][r][c] = I[pi][ri][ci]
ci = ci + 1
if ci >= Ci then ci = 0, ri = ri + 1
if ri >= Ri then ri = 0, pi = pi + 1

```

The pseudo-code has the following meaning:

Pseudo-code Meaning
p Output-Parallel-Index
pi Input-Parallel-Index
r Output-Kernel-Row-Index
ri Input-Kernel-Row-Index
c Output-Kernel-Column-Index
co Output-Kernel-Column-Index
Pi Input-Parallelism
P Output-Parallelism
Ri Input-Kernel-Rows
R Input-Kernel-Columns
Ci Input-KernelColumns
C OutputKernelColumns

Table 30. Explanation of pseudo-code

The function of the CastKernel operator could also be achieved by combining the follwoing operators: SplitKernel, MergeKernel, SplitParallel and MergeParallel:

In this example, the input configuration of four kernel columns and two kernel rows at parallelism 3 is re-organised to two kernel columns and three kernel rows at parallelism 4. The same can be achieved with the operator CastKernel by configuring the output link respectively:

### I/O Properties

Property Value
Operator Type O

Bit Width [1, 64] As I
Arithmetic {Unsigned, signed} As I
Parallelism Any Auto
Kernel Columns Any Any
Kernel Rows Any Any
Img Protocol {VALT_IMAGE2D, VALT_LINE1D, VALT_PIXEL0D} As I
Color Format Any As I
Color Flavor Any As I
Max. Img Width Any Auto
Max. Img Height Any As I
 The range for bit width is: For unsigned inputs: [1, 64] For signed inputs: [2, 64] For unsigned color inputs: [3, 63] For signed color inputs: [6, 63] The output parallelism is determined by the input parallelism , the input kernel size and the output kernel size : where denotes the kernel rows and denotes the kernel columns. The output maximum image width is determined by the input maximum image width, the output parallelism and the input parallelism by:

None

### Examples of Use

The use of operator CastKernel is shown in the following examples: