# Pixel-Processing Accelerator (PPA)

## Introduction

ESP32-P4 includes a pixel-processing accelerator (PPA) module, to realize hardware-level acceleration of image algorithms, such as image rotation, scaling, mirroring, and blending.

## Terminology

The terms used in relation to the PPA driver are given in the table and the diagram below.

Term | Definition
--- | ---
Picture (pic) | A complete image stored in the system memory.
Block | A portion cropped from a picture at a certain size, with the maximum size equivalent to the entire picture.
Pixel | The unit to be used in the PPA context.
PPA Operation | Types of image algorithm accelerations, includes scale-rotate-mirror (SRM), blend, and fill.
PPA Client | Who wants to do the PPA operations. Typically, every PPA client is hold by a specific task.
PPA Transaction | One request from a PPA client to do a PPA operation is one PPA transaction.

PPA picture/block terminology

## Functional Overview

The following sections detail the design of the PPA driver:

- Register PPA Client - Covers how to register a PPA client to perform any PPA operations.

- Register PPA Event Callbacks - Covers how to hook user specific code to PPA driver event callback function.

- Perform PPA Operations - Covers how to perform a PPA operation.

- Thread Safety - Covers the usage of the PPA operation APIs in thread safety aspect.

- Performance Overview - Covers the performance of PPA operations.

### Register PPA Client

Requests to perform PPA operations are made by PPA clients. Therefore, PPA clients need to be registered first before doing any PPA operations. Call `ppa_register_client()` function to register a new client. `ppa_client_config_t` structure is used to specific the properties of the client.

- `ppa_client_config_t::oper_type` - Each PPA operation type corresponds to one PPA client type, a registered PPA client can only request one specific type of PPA operations.

- `ppa_client_config_t::max_pending_trans_num` - Decides the maximum number of pending PPA transactions the client can hold.

It is recommended that every task to register its own PPA clients. For example, an application contains two tasks: Task A requires both the PPA SRM and the PPA fill functionalities, so one PPA SRM client and one PPA fill client should be registered in Task A; While Task B also requires the PPA SRM functionality, then another PPA SRM client should be registered in Task B.

If the task no longer needs to do PPA operations, the corresponding PPA clients can be deregistered with `ppa_unregister_client()` function.

### Register PPA Event Callbacks

When an event occurs (e.g., a PPA transaction is completed), the CPU is notified of this event via an interrupt. If some specific functions need to be called when a particular event occurs, a callback can be registered for that event by calling `ppa_client_register_event_callbacks()`. This can be specifically useful when `PPA_TRANS_MODE_NON_BLOCKING` mode is selected to perform the PPA operations. It is worth noticing that the event callbacks are bound to PPA clients, but the user context is provided per transaction in the call to the PPA operation APIs. This allows the maximum flexibility in utilizing the event callbacks.

The registered callback functions are called in the interrupt context, therefore, the callback functions should follow common ISR (Interrupt Service Routine) rules.

### Perform PPA Operations

Once the PPA client is registered, a PPA operation can be requested with the returned `ppa_client_handle_t`.

PPA operations includes:

#### Scale, Rotate, Mirror (SRM)

Call `ppa_do_scale_rotate_mirror()` to apply one or more of the scaling, rotation, mirroring operations to the target block inside a picture.

Some notes to avoid confusion in configuring `ppa_srm_oper_config_t`:

- `ppa_in_pic_blk_config_t::buffer` and `ppa_out_pic_blk_config_t::buffer` have to be the pointers to different picture buffers for a SRM operation.

- The precision of `ppa_srm_oper_config_t::scale_x` and `ppa_srm_oper_config_t::scale_y` will be truncated to a step size of 1/16.

- Output block's width/height is totally determined by the input block's width/height, scaling factor, and rotation angle, so output block's width/height does not need to be configured. However, please make sure the output block can fit at the offset location in the output picture.

- If the color mode of the input or output picture is `PPA_SRM_COLOR_MODE_YUV420`, then its `pic_w`, `pic_h`, `block_w`, `block_h`, `block_offset_x`, `block_offset_y` fields must be even.

Note

The PPA SRM internally uses bilinear scaling algorithm to process. Therefore, it may cause chromatic aberration and loss of contrast at the edges in a scaled picture.

#### Blend

Call `ppa_do_blend()` to blend the two target blocks of two so-called foreground (FG) and background (BG) pictures.

Blend follows the normal Alpha Blending formula:

\(A_{out} = A_b + A_f - A_b \times A_f\)

\(C_{out} = (C_b \times A_b \times (1 - A_f) + C_f \times A_f) / (A_b + A_f - A_b \times A_f)\)

where \(A_b\) is the Alpha channel of the background layer, \(A_f\) is the Alpha channel of the foreground layer, \(C_b\) corresponds to the R, G, B components of the background layer, and \(C_f\) corresponds to the R, G, B components of the foreground layer.

Note that this formula is not symmetric to FG and BG. When \(A_f = 1\), it calculates \(C_{out} = C_f\), \(A_{out} = 1\), which means if the color mode of the FG picture is `PPA_BLEND_COLOR_MODE_RGB565` or `PPA_BLEND_COLOR_MODE_RGB888`, since a Alpha value of 255 will be filled by the PPA hardware (i.e. \(A_f = 1\)), the blended result will be identical to the FG block.

If `ppa_blend_oper_config_t::bg_ck_en` or `ppa_blend_oper_config_t::fg_ck_en` is set to `true`, the pixels fall into the color-key (also known as Chroma-key) range does not follow Alpha Blending process. Please check ESP32-P4 Technical Reference Manual > Pixel-Processing Accelerator (PPA) > Functional Description > Layer Blending (BLEND) [PDF] for the detailed rules.

Similarly, some notes to avoid confusion in configuring `ppa_blend_oper_config_t`:

- `ppa_out_pic_blk_config_t::buffer` can be the same pointer to one of the input's `ppa_in_pic_blk_config_t::buffer` for a blend operation.

- The blocks' width/height of FG and BG should be identical, and are the width/height values for the output block.

- If the color mode of the input picture is `PPA_BLEND_COLOR_MODE_A4`, then its `block_w` and `block_offset_x` fields must be even.

#### Fill

Call `ppa_do_fill()` to fill a target block inside a picture.

`ppa_trans_mode_t` is a field configurable to all the PPA operation APIs. It decides whether you want the call to the PPA operation API to block until the transaction finishes or to return immediately after the transaction is pushed to the internal queue.

### Thread Safety

The PPA driver has guaranteed the thread safety of calling the PPA operation APIs in all following situations:

- Among clients of different types in one task

- Among clients of same type in different tasks

- Among clients of different types in different tasks

### Performance Overview

The PPA operations are acted on the target block of an input picture. Therefore, the time it takes to complete a PPA transaction is proportional to the amount of the data in the block. The size of the entire picture has no influence on the performance. More importantly, the PPA performance highly relies on the PSRAM bandwidth if the pictures are located in the PSRAM section. When there are quite a few peripherals reading and writing to the PSRAM at the same time, the performance of PPA operation will be greatly reduced.

## API Reference

### Header File

- components/esp_driver_ppa/include/driver/ppa.h

- This header file can be included with:

  >     #include "driver/ppa.h"

- This header file is a part of the API provided by the `esp_driver_ppa` component. To declare that your component depends on `esp_driver_ppa`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_driver_ppa

  > or

  >     PRIV_REQUIRES esp_driver_ppa

### Functions

esp_err_t ppa_register_client(const ppa_client_config_t *config, ppa_client_handle_t *ret_client)

  Register a PPA client to do a specific PPA operation.

  Parameters:

    - config -- [in] Pointer to a collection of configurations for the client

    - ret_client -- [out] Returned client handle

  Returns:

    - ESP_OK: Register the PPA client successfully

    - ESP_ERR_INVALID_ARG: Register the PPA client failed because of invalid argument

    - ESP_ERR_NO_MEM: Register the PPA client failed because out of memory

    - ESP_FAIL: Register the PPA client failed because of other error

esp_err_t ppa_unregister_client(ppa_client_handle_t ppa_client)

  Unregister a PPA client.

  Note

  This will also free the resources occupied by the client

  Parameters:

    ppa_client -- [in] PPA client handle, allocated by `ppa_register_client`

  Returns:

    - ESP_OK: Unregister the PPA client successfully

    - ESP_ERR_INVALID_ARG: Unregister the PPA client failed because of invalid argument

    - ESP_ERR_INVALID_STATE: Unregister the PPA client failed because there are unfinished transactions

esp_err_t ppa_client_register_event_callbacks(ppa_client_handle_t ppa_client, const ppa_event_callbacks_t *cbs)

  Register event callbacks for a PPA client.

  Note

  Any user private data that wants to be passed directly to callback's user_data is provided per PPA transaction. Please check the `user_data` field in `ppa_xxx_oper_config_t` structure.

  Parameters:

    - ppa_client -- [in] PPA client handle

    - cbs -- [in] Structure with all PPA callbacks

  Returns:

    - ESP_OK: Register event callbacks for the PPA client successfully

    - ESP_ERR_INVALID_ARG: Register event callbacks for the PPA client failed because of invalid argument

esp_err_t ppa_do_scale_rotate_mirror(ppa_client_handle_t ppa_client, const ppa_srm_oper_config_t *config)

  Perform a scaling-rotating-mirroring (SRM) operation to a picture.

  Parameters:

    - ppa_client -- [in] PPA client handle that has been registered to do SRM operations

    - config -- [in] Pointer to a collection of configurations for the SRM operation transaction, ppa_srm_oper_config_t

  Returns:

    - ESP_OK: Perform a SRM operation successfully

    - ESP_ERR_INVALID_ARG: Perform a SRM operation failed because of invalid argument

    - ESP_FAIL: Perform a SRM operation failed because the client's pending transactions has reached its maximum capacity

esp_err_t ppa_do_blend(ppa_client_handle_t ppa_client, const ppa_blend_oper_config_t *config)

  Perform a blending operation to a picture.

  Parameters:

    - ppa_client -- [in] PPA client handle that has been registered to do blend operations

    - config -- [in] Pointer to a collection of configurations for the blend operation transaction, ppa_blend_oper_config_t

  Returns:

    - ESP_OK: Perform a blend operation successfully

    - ESP_ERR_INVALID_ARG: Perform a blend operation failed because of invalid argument

    - ESP_FAIL: Perform a blend operation failed because the client's pending transactions has reached its maximum capacity

esp_err_t ppa_do_fill(ppa_client_handle_t ppa_client, const ppa_fill_oper_config_t *config)

  Perform a filling operation to a picture.

  Parameters:

    - ppa_client -- [in] PPA client handle that has been registered to do fill operations

    - config -- [in] Pointer to a collection of configurations for the fill operation transaction, ppa_fill_oper_config_t

  Returns:

    - ESP_OK: Perform a fill operation successfully

    - ESP_ERR_INVALID_ARG: Perform a fill operation failed because of invalid argument

    - ESP_FAIL: Perform a fill operation failed because the client's pending transactions has reached its maximum capacity

### Structures

struct ppa_client_config_t

  A collection of configuration items that used for registering a PPA client.

  Public Members

  ppa_operation_t oper_type

    The desired PPA operation for the client

  uint32_t max_pending_trans_num

    The maximum number of pending transactions for the client. By default, it will be 1, which is sufficient if all transactions are performed with `PPA_TRANS_MODE_BLOCKING`

  ppa_data_burst_length_t data_burst_length

    The desired data burst length for all the transactions of the client. Use a small burst length will decrease PPA performance, but can save burst bandwidth for other peripheral usages. By default, it will be at the maximum burst length, `PPA_DATA_BURST_LENGTH_128`

struct ppa_event_data_t

  Type of PPA event data.

struct ppa_event_callbacks_t

  Group of supported PPA callbacks.

  Public Members

  ppa_event_callback_t on_trans_done

    Invoked when a PPA transaction finishes

struct ppa_in_pic_blk_config_t

  A collection of configuration items for an input picture and the target block inside the picture.

  Public Members

  const void *buffer

    Pointer to the input picture buffer

  uint32_t pic_w

    Input picture width (unit: pixel)

  uint32_t pic_h

    Input picture height (unit: pixel)

  uint32_t block_w

    Target block width (unit: pixel)

  uint32_t block_h

    Target block height (unit: pixel)

  uint32_t block_offset_x

    Target block offset in x direction in the picture (unit: pixel)

  uint32_t block_offset_y

    Target block offset in y direction in the picture (unit: pixel)

  ppa_srm_color_mode_t srm_cm

    Color mode of the picture in a PPA SRM operation. Supported color mode in `ppa_srm_color_mode_t`

  ppa_blend_color_mode_t blend_cm

    Color mode of the picture in a PPA blend operation. Supported color mode in `ppa_blend_color_mode_t`

  ppa_fill_color_mode_t fill_cm

    Color mode of the picture in a PPA fill operation. Supported color mode in `ppa_fill_color_mode_t`

  ppa_color_range_t yuv_range

    When the color mode is any YUV color space, this field is to describe its color range

  ppa_color_conv_std_rgb_yuv_t yuv_std

    When the color mode is any YUV color space, this field is to describe its YUV<->RGB conversion standard

struct ppa_out_pic_blk_config_t

  A collection of configuration items for an output picture and the target block inside the picture.

  Public Members

  void *buffer

    Pointer to the output picture buffer (requires alignment: internal memory needs align to L1 cache line size, external memory needs align to L1 and L2 cache line size)

  uint32_t buffer_size

    Size of the output picture buffer (requires alignment: internal memory needs align to L1 cache line size, external memory needs align to L1 and L2 cache line size)

  uint32_t pic_w

    Output picture width (unit: pixel)

  uint32_t pic_h

    Output picture height (unit: pixel)

  uint32_t block_offset_x

    Target block offset in x direction in the picture (unit: pixel)

  uint32_t block_offset_y

    Target block offset in y direction in the picture (unit: pixel)

  ppa_srm_color_mode_t srm_cm

    Color mode of the picture in a PPA SRM operation. Supported color mode in `ppa_srm_color_mode_t`

  ppa_blend_color_mode_t blend_cm

    Color mode of the picture in a PPA blend operation. Supported color mode in `ppa_blend_color_mode_t`

  ppa_fill_color_mode_t fill_cm

    Color mode of the picture in a PPA fill operation. Supported color mode in `ppa_fill_color_mode_t`

  ppa_color_range_t yuv_range

    When the color mode is any YUV color space, this field is to describe its color range

  ppa_color_conv_std_rgb_yuv_t yuv_std

    When the color mode is any YUV color space, this field is to describe its YUV<->RGB conversion standard

struct ppa_srm_oper_config_t

  A collection of configuration items to do a PPA SRM operation transaction.

  Public Members

  ppa_in_pic_blk_config_t in

    Information of the input picture and the target block

  ppa_out_pic_blk_config_t out

    Information of the output picture and the target block

  ppa_srm_rotation_angle_t rotation_angle

    Rotation (counter-clockwise) to the target block, select from `ppa_srm_rotation_angle_t`

  float scale_x

    Scaling factor to the target block in the x direction

  float scale_y

    Scaling factor to the target block in the y direction

  bool mirror_x

    Whether to mirror the target block in the x direction

  bool mirror_y

    Whether to mirror the target block in the y direction

  bool rgb_swap

    Whether to swap the input data in RGB (e.g. ARGB becomes BGRA, RGB becomes BGR)

  bool byte_swap

    Whether to swap the input data in byte. Only available feature if input picture color mode is ARGB8888 or RGB565

  ppa_alpha_update_mode_t alpha_update_mode

    Select whether the alpha channel of the input picture needs update

  uint32_t alpha_fix_val

    Range: [0, 255] When PPA_ALPHA_FIX_VALUE mode is selected, alpha_fix_val is the new alpha value to replace the input alpha value (output_alpha = alpha_fix_val)

  float alpha_scale_ratio

    Range: (0, 1) When PPA_ALPHA_SCALE mode is selected, alpha_scale_ratio is the multiplier to the input alpha value (output_alpha = alpha_scale_ratio * input_alpha) Ratio resolution is 1/256

  ppa_trans_mode_t mode

    Determines whether to block inside the operation functions, see `ppa_trans_mode_t`

  void *user_data

    User registered data to be passed into `done_cb` callback function

struct ppa_blend_oper_config_t

  A collection of configuration items to do a PPA blend operation transaction.

  Public Members

  ppa_in_pic_blk_config_t in_bg

    Information of the input background picture and the target block

  ppa_in_pic_blk_config_t in_fg

    Information of the input foreground picture and the target block

  ppa_out_pic_blk_config_t out

    Information of the output picture and the target block

  bool bg_rgb_swap

    Whether to swap the background input data in RGB (e.g. ARGB becomes BGRA, RGB becomes BGR)

  bool bg_byte_swap

    Whether to swap the background input data in byte. Only available feature if input BG picture color mode is ARGB8888 or RGB565

  ppa_alpha_update_mode_t bg_alpha_update_mode

    Select whether the alpha channel of the input background picture needs update

  uint32_t bg_alpha_fix_val

    Range: [0, 255] When PPA_ALPHA_FIX_VALUE mode is selected, alpha_fix_val is the new alpha value to replace the input alpha value (output_alpha = alpha_fix_val)

  float bg_alpha_scale_ratio

    Range: (0, 1) When PPA_ALPHA_SCALE mode is selected, alpha_scale_ratio is the multiplier to the input alpha value (output_alpha = alpha_scale_ratio * input_alpha) Ratio resolution is 1/256

  bool fg_rgb_swap

    Whether to swap the foreground input data in RGB (e.g. ARGB becomes BGRA, RGB becomes BGR)

  bool fg_byte_swap

    Whether to swap the foreground input data in byte. Only available feature if input FG picture color mode is ARGB8888 or RGB565

  ppa_alpha_update_mode_t fg_alpha_update_mode

    Select whether the alpha channel of the input foreground picture needs update

  uint32_t fg_alpha_fix_val

    Range: [0, 255] When PPA_ALPHA_FIX_VALUE mode is selected, alpha_fix_val is the new alpha value to replace the input alpha value (output_alpha = alpha_fix_val)

  float fg_alpha_scale_ratio

    Range: (0, 1) When PPA_ALPHA_SCALE mode is selected, alpha_scale_ratio is the multiplier to the input alpha value (output_alpha = alpha_scale_ratio * input_alpha) Ratio resolution is 1/256

  color_pixel_rgb888_data_t fg_fix_rgb_val

    When in_fg.blend_cm is PPA_BLEND_COLOR_MODE_A8/4, this field can be used to set a fixed color for the foreground, in RGB888 format

  bool bg_ck_en

    Whether to enable color keying for background If not enabled, all background pixels are considered as out of the color-keying range

  color_pixel_rgb888_data_t bg_ck_rgb_low_thres

    The lower threshold of the color-keying range for the background, in RGB888 format

  color_pixel_rgb888_data_t bg_ck_rgb_high_thres

    The higher threshold of the color-keying range for the background, in RGB888 format

  bool fg_ck_en

    Whether to enable color keying for foreground If not enabled, all foreground pixels are considered as out of the color-keying range

  color_pixel_rgb888_data_t fg_ck_rgb_low_thres

    The lower threshold of the color-keying range for the foreground, in RGB888 format

  color_pixel_rgb888_data_t fg_ck_rgb_high_thres

    The higher threshold of the color-keying range for the foreground, in RGB888 format

  color_pixel_rgb888_data_t ck_rgb_default_val

    The color to overwrite when a pixel, where its background element and foreground element are both within their color-keying ranges, in RGB888 format

  bool ck_reverse_bg2fg

    If this bit is set, in color-keying, for the pixel, where its background element is in the color range, but its foreground element is not in the color range, it will output the foreground element instead of the background element

  ppa_trans_mode_t mode

    Determines whether to block inside the operation functions, see `ppa_trans_mode_t`

  void *user_data

    User registered data to be passed into `done_cb` callback function

struct ppa_fill_oper_config_t

  A collection of configuration items to do a PPA fill operation transaction.

  Public Members

  ppa_out_pic_blk_config_t out

    Information of the output picture and the target block

  uint32_t fill_block_w

    The width of the block to be filled (unit: pixel)

  uint32_t fill_block_h

    The height of the block to be filled (unit: pixel)

  color_pixel_argb8888_data_t fill_argb_color

    The color to be filled, in ARGB8888 format

  ppa_trans_mode_t mode

    Determines whether to block inside the operation functions, see `ppa_trans_mode_t`

  void *user_data

    User registered data to be passed into `done_cb` callback function

### Type Definitions

typedef struct ppa_client_t *ppa_client_handle_t

  Type of PPA client handle.

typedef bool (*ppa_event_callback_t)(ppa_client_handle_t ppa_client, ppa_event_data_t *event_data, void *user_data)

  Type of PPA event callback.

  Param ppa_client:

    [in] PPA client handle

  Param event_data:

    [in] PPA event data

  Param user_data:

    [in] User registered data from calling `ppa_do_xxx` to perform an operation

  Return:

    Whether a task switch is needed after the callback function returns, this is usually due to the callback wakes up some high priority task.

### Enumerations

enum ppa_operation_t

  Enumeration of all PPA available operations.

  Values:

  enumerator PPA_OPERATION_SRM

    Do scale-rotate-mirror operation

  enumerator PPA_OPERATION_BLEND

    Do blend operation

  enumerator PPA_OPERATION_FILL

    Do fill operation, use one constant pixel to fill a target window

  enumerator PPA_OPERATION_INVALID

    Invalid PPA operations, indicates the quantity of available PPA operations

enum ppa_trans_mode_t

  Modes to perform the PPA operations.

  Values:

  enumerator PPA_TRANS_MODE_BLOCKING

    `ppa_do_xxx` function will block until the PPA operation is finished

  enumerator PPA_TRANS_MODE_NON_BLOCKING

    `ppa_do_xxx` function will return immediately after the PPA operation is pushed to the internal queue

### Header File

- components/hal/include/hal/ppa_types.h

- This header file can be included with:

  >     #include "hal/ppa_types.h"

### Enumerations

enum ppa_engine_type_t

  Enumeration of engines in PPA modules.

  Values:

  enumerator PPA_ENGINE_TYPE_SRM

    PPA Scaling-Rotating-Mirroring (SRM) engine, used to perform scale, rotate, mirror

  enumerator PPA_ENGINE_TYPE_BLEND

    PPA Blending engine, used to perform blend or fill

enum ppa_srm_rotation_angle_t

  Enumeration of PPA Scaling-Rotating-Mirroring available rotation angle (in the counterclockwise direction)

  Values:

  enumerator PPA_SRM_ROTATION_ANGLE_0

    Picture does no rotation

  enumerator PPA_SRM_ROTATION_ANGLE_90

    Picture rotates 90 degrees CCW

  enumerator PPA_SRM_ROTATION_ANGLE_180

    Picture rotates 180 degrees CCW

  enumerator PPA_SRM_ROTATION_ANGLE_270

    Picture rotates 270 degrees CCW

enum ppa_srm_color_mode_t

  Enumeration of PPA Scaling-Rotating-Mirroring available color mode.

  Values:

  enumerator PPA_SRM_COLOR_MODE_ARGB8888

    PPA SRM color mode: ARGB8888

  enumerator PPA_SRM_COLOR_MODE_RGB888

    PPA SRM color mode: RGB888

  enumerator PPA_SRM_COLOR_MODE_RGB565

    PPA SRM color mode: RGB565

  enumerator PPA_SRM_COLOR_MODE_YUV420

    PPA SRM color mode: YUV420

  enumerator PPA_SRM_COLOR_MODE_YUV444

    PPA SRM color mode: YUV444 (limited range only and can only be the input color mode)

enum ppa_blend_color_mode_t

  Enumeration of PPA blend available color mode.

  Values:

  enumerator PPA_BLEND_COLOR_MODE_ARGB8888

    PPA blend color mode: ARGB8888

  enumerator PPA_BLEND_COLOR_MODE_RGB888

    PPA blend color mode: RGB888

  enumerator PPA_BLEND_COLOR_MODE_RGB565

    PPA blend color mode: RGB565

  enumerator PPA_BLEND_COLOR_MODE_A8

    PPA blend color mode: A8, only available on blend foreground input

  enumerator PPA_BLEND_COLOR_MODE_A4

    PPA blend color mode: A4, only available on blend foreground input

enum ppa_fill_color_mode_t

  Enumeration of PPA fill available color mode.

  Values:

  enumerator PPA_FILL_COLOR_MODE_ARGB8888

    PPA fill color mode: ARGB8888

  enumerator PPA_FILL_COLOR_MODE_RGB888

    PPA fill color mode: RGB888

  enumerator PPA_FILL_COLOR_MODE_RGB565

    PPA fill color mode: RGB565

enum ppa_alpha_update_mode_t

  Enumeration of PPA alpha compositing update mode.

  Values:

  enumerator PPA_ALPHA_NO_CHANGE

    Do not replace alpha value (A' = A). If input format does not contain alpha info, alpha value 255 will be used.

  enumerator PPA_ALPHA_FIX_VALUE

    Replace the alpha value in received pixel with a new, fixed alpha value (A' = val)

  enumerator PPA_ALPHA_SCALE

    Scale the alpha value in received pixel to be a new alpha value (A' = (A * val) >> 8). If input format does not contain alpha info, A' = (255 * val) >> 8.

  enumerator PPA_ALPHA_INVERT

    Invert the alpha value in received pixel (A' = 255 - A). If input format does not contain alpha info, A' = 0, i.e. a layer with 0% opacity.

enum ppa_color_conv_std_rgb_yuv_t

  Enumeration of PPA supported color conversion standard between RGB and YUV (determines the YUV<->RGB conversion equation)

  Values:

  enumerator PPA_COLOR_CONV_STD_RGB_YUV_BT601

    YUV<->RGB conversion standard: BT.601

  enumerator PPA_COLOR_CONV_STD_RGB_YUV_BT709

    YUV<->RGB conversion standard: BT.709

enum ppa_color_range_t

  Enumeration of PPA supported color range (determines the YUV<->RGB conversion equation)

  Values:

  enumerator PPA_COLOR_RANGE_LIMIT

    Limited color range, 16 is the darkest black and 235 is the brightest white

  enumerator PPA_COLOR_RANGE_FULL

    Full color range, 0 is the darkest black and 255 is the brightest white

enum ppa_data_burst_length_t

  Enumeration of PPA supported data burst length.

  Values:

  enumerator PPA_DATA_BURST_LENGTH_8

    Data burst length: 8 bytes

  enumerator PPA_DATA_BURST_LENGTH_16

    Data burst length: 16 bytes

  enumerator PPA_DATA_BURST_LENGTH_32

    Data burst length: 32 bytes

  enumerator PPA_DATA_BURST_LENGTH_64

    Data burst length: 64 bytes

  enumerator PPA_DATA_BURST_LENGTH_128

    Data burst length: 128 bytes

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