# JPEG Encoder and Decoder

[中文]

## Introduction

JPEG is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The compression level varies with changes in image size and compression quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality.

JPEG codec on ESP32-S31 is an image codec, which is based on the JPEG baseline standard, for compressing and decompressing images to reduce the bandwidth required to transmit images or the space required to store images, making it possible to process large-resolution images. But please note, at one time, the codec engine can only work as either encoder or decoder.

For more hardware features of JPEG codec, please refer to the JPEG codec section in ESP32-S31 Technical Reference Manual, for more details.

## Functional Overview

This document covers the following sections:

- Resource Allocation - covers how to allocate JPEG resources with properly set of configurations. It also covers how to recycle the resources when they finished working.

- Finite State Machine - covers JPEG workflow. Introduce how jpeg driver uses internal resources and its software process.

- JPEG Decoder Engine - covers behavior of JPEG decoder engine. Introduce how to use decoder engine functions to decode an image (from jpg format to raw format).

- JPEG Encoder Engine - covers behavior of JPEG encoder engine. Introduce how to use encoder engine functions to encode an image (from raw format to jpg format).

- Performance Overview - covers encoder and decoder performance.

- Pixel Storage Layout for Different Color Formats - covers color space order overview required in this JPEG decoder and encoder.

- Thread Safety - lists which APIs are guaranteed to be thread safe by the driver.

- Power Management - describes how JPEG driver would be affected by power consumption.

- Kconfig Options - lists the supported Kconfig options that can bring different effects to the driver.

### Resource Allocation

#### Install JPEG decoder engine

JPEG decoder engine requires the configuration that specified by `jpeg_decode_engine_cfg_t`.

If the configurations in `jpeg_decode_engine_cfg_t` is specified, users can call `jpeg_new_decoder_engine()` to allocate and initialize a JPEG decoder engine. This function will return an JPEG decoder handle if it runs correctly. You can take following code as reference.

    jpeg_decoder_handle_t decoder_engine;

    jpeg_decode_engine_cfg_t decode_eng_cfg = {
        .intr_priority = 0,
        .timeout_ms = 40,
    };

    ESP_ERROR_CHECK(jpeg_new_decoder_engine(&decode_eng_cfg, &decoder_engine));

#### Uninstall JPEG decoder engine

If a previously installed JPEG engine is no longer needed, it's recommended to recycle the resource by calling `jpeg_del_decoder_engine()`, so that the underlying hardware is released.

    ESP_ERROR_CHECK(jpeg_del_decoder_engine(decoder_engine));

#### Install JPEG encoder engine

The JPEG encoder engine requires the configuration specified by `jpeg_encode_engine_cfg_t`.

If the configurations in `jpeg_encode_engine_cfg_t` is specified, users can call `jpeg_new_encoder_engine()` to allocate and initialize a JPEG encoder engine. This function will return an JPEG encoder handle if it runs correctly. You can take following code as reference.

    jpeg_encoder_handle_t encoder_engine;

    jpeg_encode_engine_cfg_t encode_eng_cfg = {
        .intr_priority = 0,
        .timeout_ms = 40,
    };

    ESP_ERROR_CHECK(jpeg_new_encoder_engine(&encode_eng_cfg, &encoder_engine));

#### Uninstall JPEG encoder engine

If a previously installed JPEG engine is no longer needed, it's recommended to recycle the resource by calling `jpeg_del_encoder_engine()`, so that the underlying hardware is released.

    ESP_ERROR_CHECK(jpeg_del_encoder_engine(encoder_engine));

### Finite State Machine

The JPEG driver usage of hardware resources and its process workflow are shown in the following graph:

JPEG finite state machine

### JPEG Decoder Engine

After installing the JPEG decoder driver by `jpeg_new_decoder_engine()`, ESP32-S31 is ready to decode JPEG pictures by `jpeg_decoder_process()`. `jpeg_decoder_process()` is flexible for decoding different types of pictures by a configurable parameter called `jpeg_decode_cfg_t`.

Moreover, our JPEG decoder API provides a helper function which helps you get the basic information of your given image. Calling `jpeg_decoder_get_info()` would return the picture information structure called `jpeg_decoder_get_info()`. If you already know the picture basic information, this functions is unnecessary to be called.

The format conversions supported by this driver are listed in the table below:

Format of the already compressed image | Format after decompressing
--- | ---
YUV444 | RGB565/RGB888
YUV422 | RGB565/RGB888
YUV420 | RGB565/RGB888
GRAY | GRAY

Overall, You can take following code as reference, the code is going to decode a 1080*1920 picture.

    jpeg_decode_cfg_t decode_cfg_rgb = {
        .output_format = JPEG_DECODE_OUT_FORMAT_RGB888,
        .rgb_order = JPEG_DEC_RGB_ELEMENT_ORDER_BGR,
    };

    size_t tx_buffer_size;
    size_t rx_buffer_size;

    jpeg_decode_memory_alloc_cfg_t rx_mem_cfg = {
        .buffer_direction = JPEG_DEC_ALLOC_OUTPUT_BUFFER,
    };

    jpeg_decode_memory_alloc_cfg_t tx_mem_cfg = {
        .buffer_direction = JPEG_DEC_ALLOC_INPUT_BUFFER,
    };

    uint8_t *bit_stream = (uint8_t*)jpeg_alloc_decoder_mem(jpeg_size, &tx_mem_cfg, &tx_buffer_size);
    uint8_t *out_buf = (uint8_t*)jpeg_alloc_decoder_mem(1920 * 1088 * 3, &rx_mem_cfg, &rx_buffer_size);

    jpeg_decode_picture_info_t header_info;
    ESP_ERROR_CHECK(jpeg_decoder_get_info(bit_stream, bit_stream_size, &header_info));
    uint32_t out_size = 0;
    ESP_ERROR_CHECK(jpeg_decoder_process(decoder_engine, &decode_cfg_rgb, bit_stream, bit_stream_size, out_buf, &out_size));

There are some tips that can help you use this driver more accurately:

1. In above code, you should make sure the bit_stream and out_buf should be aligned by certain rules. We provide a helper function `jpeg_alloc_decoder_mem()` to help you malloc a buffer which is aligned in both size and address.

2. The content of bit_stream buffer should not be changed until `jpeg_decoder_process()` returns.

3. The width and height of output picture would be 16 bytes aligned if original picture is compressed by YUV420 or YUV422. For example, if the input picture is 1080*1920, the output picture will be 1088*1920. That is the restriction of jpeg protocol. Please provide sufficient output buffer memory.

### JPEG Encoder Engine

After installing the JPEG encoder driver by `jpeg_new_encoder_engine()`, ESP32-S31 is ready to encode JPEG pictures by `jpeg_encoder_process()`. `jpeg_encoder_process()` is flexible for decoding different types of pictures by a configurable parameter called `jpeg_encode_cfg_t`.

The format conversions supported by this driver are listed in the table below:

Format of Original Image | Down sampling method
--- | ---
RGB565/RGB888 | YUV444/YUV422/YUV420
GRAY | GRAY

Below is the example of code that encodes a 1080*1920 picture:

    int raw_size_1080p = 0;/* Your raw image size */
    jpeg_encode_cfg_t enc_config = {
        .src_type = JPEG_ENCODE_IN_FORMAT_RGB888,
        .sub_sample = JPEG_DOWN_SAMPLING_YUV422,
        .image_quality = 80,
        .width = 1920,
        .height = 1080,
        .pixel_reverse = false, // Whether to reverse the pixel order of the input image, or pixel order detail please refer to technical reference manual
    };

    uint8_t *raw_buf_1080p = (uint8_t*)jpeg_alloc_encoder_mem(raw_size_1080p);
    if (raw_buf_1080p == NULL) {
        ESP_LOGE(TAG, "alloc 1080p tx buffer error");
        return;
    }
    uint8_t *jpg_buf_1080p = (uint8_t*)jpeg_alloc_encoder_mem(raw_size_1080p / 10); // Assume that compression ratio of 10 to 1
    if (jpg_buf_1080p == NULL) {
        ESP_LOGE(TAG, "alloc jpg_buf_1080p error");
        return;
    }

    ESP_ERROR_CHECK(jpeg_encoder_process(jpeg_handle, &enc_config, raw_buf_1080p, raw_size_1080p, jpg_buf_1080p, &jpg_size_1080p););

There are some tips that can help you use this driver more accurately:

1. In above code, you should make sure the raw_buf_1080p and jpg_buf_1080p should aligned by calling `jpeg_alloc_encoder_mem()`.

2. The content of raw_buf_1080p buffer should not be changed until `jpeg_encoder_process()` returns.

3. The compression ratio depends on the chosen image_quality and the content of the image itself. Generally, a higher image_quality value obviously results in better image quality but a smaller compression ratio. As for the image content, it is hard to give any specific guidelines, so this question is out of the scope of this document. Generally, the baseline JPEG compression ratio can vary from 40:1 to 10:1. Please take the actual situation into account.

### Performance Overview

This section provides some measurements of the decoder and encoder performance. The data presented in the tables below gives the average values of decoding or encoding a randomly chosen picture fragments for 50 times. All tests were performed at a CPU frequency of 360MHz and a SPI RAM clock frequency of 200MHz. Only JPEG related code is run in this test, no other modules are involved (e.g. USB Camera, etc.).

Both decoder and encoder are not cause too much CPU involvement. Only header parse causes CPU source. Calculations related to JPEG compression, such as DCT, quantization, huffman encoding/decoding, etc., are done entirely in hardware.

#### JPEG decoder performance

JPEG Height | JPEG Width | Pixel Format in [1] | Pixel Format out [2] | Performance (fps)
--- | --- | --- | --- | ---
1080 | 1920 | YUV422 | RGB888/RGB565 | 48
720 | 1280 | YUV422 | RGB888/RGB565 | 109
480 | 800 | YUV422 | RGB888/RGB565 | 253
480 | 640 | YUV422 | RGB888/RGB565 | 307
480 | 320 | YUV422 | RGB888/RGB565 | 571
720 | 1280 | GRAY | GRAY | 161

[1]

Format of the already compressed image

[2]

Format after decompressing

#### JPEG encoder performance

JPEG Height | JPEG Width | Pixel Format in [3] | Pixel Format out [4] | Performance (fps)
--- | --- | --- | --- | ---
1080 | 1920 | RGB888 | YUV422 | 26
1080 | 1920 | RGB565 | YUV422 | 36
1080 | 1920 | RGB565 | YUV420 | 40
1080 | 1920 | RGB565 | YUV444 | 24
1080 | 1920 | RGB888 | YUV422 | 26
720 | 1280 | RGB565 | YUV420 | 88
720 | 1280 | RGB565 | YUV444 | 55
720 | 1280 | RGB565 | YUV422 | 81
480 | 800 | RGB888 | YUV420 | 142
640 | 800 | RGB888 | YUV420 | 174
480 | 320 | RGB888 | YUV420 | 315
720 | 1280 | GRAY | GRAY | 163

[3]

Format of Original Image

[4]

Down sampling method

### Pixel Storage Layout for Different Color Formats

The encoder and decoder described in this guide use the same uncompressed raw image formats (RGB, YUV). Therefore, the encoder and decoder are not discussed separately in this section. The pixel layout of the following formats applies to the input direction of the encoder and the output direction of the decoder (if supported). The specific pixel layout is shown in the following figure:

#### RGB888

In the following picture, each small block means one bit.

RGB888 pixel order

For RGB888, the order can be changed via `jpeg_decode_cfg_t::rgb_order` sets the pixel to RGB order.

RGB888 pixel big endian order

#### RGB565

In the following picture, each small block means one bit.

RGB565 pixel order

For RGB565, the order can be changed via `jpeg_decode_cfg_t::rgb_order` sets the pixel to RGB order.

RGB565 pixel big endian order

#### YUV444

In the following picture, each small block means one byte.

YUV444 pixel order

#### YUV422

In the following picture, each small block means one byte.

YUV422 pixel order

#### YUV420

In the following picture, each small block means one byte.

YUV420 pixel order

### Thread Safety

The factory function `jpeg_new_decoder_engine()`, `jpeg_decoder_get_info()`, `jpeg_decoder_process()`, and `jpeg_del_decoder_engine()` are guaranteed to be thread safe by the driver, which means, user can call them from different RTOS tasks without protection by extra locks.

### Power Management

When power management is enabled (i.e., CONFIG_PM_ENABLE is set), the system needs to adjust or stop the source clock of JPEG to enter Light-sleep, thus potentially changing the JPEG decoder or encoder process. This might lead to unexpected behavior in hardware calculation. To prevent such issues, entering Light-sleep is disabled for the time when JPEG encoder or decoder is working.

Whenever the user is decoding or encoding via JPEG (i.e., calling `jpeg_encoder_process()` or `jpeg_decoder_process()`), the driver guarantees that the power management lock is acquired by setting it to `esp_pm_lock_type_t::ESP_PM_CPU_FREQ_MAX`. Once the encoding or decoding is finished, the driver releases the lock and the system can enter Light-sleep.

### Kconfig Options

- CONFIG_JPEG_ENABLE_DEBUG_LOG is used to enable the debug log at the cost of increased firmware binary size.

## Maintainers' Notes

The JPEG driver usage of hardware resources and its dependency status are shown in the following graph:

JPEG driver file structure

## Application Examples

- peripherals/jpeg/jpeg_decode demonstrates how to use the JPEG hardware decoder to decode JPEG pictures of different sizes (1080p and 720p) into RGB format, showcasing the flexibility and speed of hardware decoding.

- peripherals/jpeg/jpeg_encode demonstrates how to use the JPEG hardware encoder to encode a 1080p picture, specifically converting *.rgb files to *.jpg files.

## API Reference

### Header File

- components/esp_driver_jpeg/include/driver/jpeg_decode.h

- This header file can be included with:

  >     #include "driver/jpeg_decode.h"

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

  >     REQUIRES esp_driver_jpeg

  > or

  >     PRIV_REQUIRES esp_driver_jpeg

### Functions

esp_err_t jpeg_new_decoder_engine(const jpeg_decode_engine_cfg_t *dec_eng_cfg, jpeg_decoder_handle_t *ret_decoder)

  Acquire a JPEG decode engine with the specified configuration.

  This function acquires a JPEG decode engine with the specified configuration. The configuration parameters are provided through the `dec_eng_cfg` structure, and the resulting JPEG decoder handle is returned through the `ret_decoder` pointer.

  Parameters:

    - dec_eng_cfg -- [in] Pointer to the JPEG decode engine configuration.

    - ret_decoder -- [out] Pointer to a variable that will receive the JPEG decoder handle.

  Returns:

    - ESP_OK: JPEG decoder initialized successfully.

    - ESP_ERR_INVALID_ARG: JPEG decoder initialization failed because of invalid argument.

    - ESP_ERR_NO_MEM: Create JPEG decoder failed because of out of memory.

esp_err_t jpeg_decoder_get_info(const uint8_t *bit_stream, uint32_t stream_size, jpeg_decode_picture_info_t *picture_info)

  Helper function for getting information about a JPEG image.

  This function analyzes the provided JPEG image data and retrieves information about the image, such as its width, height. The image data is specified by the `bit_stream` pointer and the `stream_size` parameter. The resulting image information is returned through the `picture_info` structure.

  Note

  This function doesn't depend on any jpeg hardware, it helps user to know jpeg information from jpeg header. For example, user can get picture width and height via this function and malloc a reasonable size buffer for jpeg engine process.

  Parameters:

    - bit_stream -- [in] Pointer to the buffer containing the JPEG image data.

    - stream_size -- [in] Size of the JPEG image data in bytes. Note that parse beginning partial of picture also works, but the beginning partial should be enough given.

    - picture_info -- [out] Pointer to the structure that will receive the image information.

  Returns:

    - ESP_OK: JPEG decoder get jpg image header successfully.

    - ESP_ERR_INVALID_ARG: JPEG decoder get header info failed because of invalid argument.

esp_err_t jpeg_decoder_process(jpeg_decoder_handle_t decoder_engine, const jpeg_decode_cfg_t *decode_cfg, const uint8_t *bit_stream, uint32_t stream_size, uint8_t *decode_outbuf, uint32_t outbuf_size, uint32_t *out_size)

  Process a JPEG image with the specified decoder instance.

  This function processes the provided JPEG image data using the specified JPEG decoder instance. The input JPEG image data is specified by the `bit_stream` pointer and the `stream_size` parameter. The resulting decoded image data is written to the `decode_outbuf` buffer, and the length of the output image data is returned through the `out_size` pointer.

  Note

  1.Please make sure that the content of `bit_stream` pointer cannot be modified until this function returns. 2.Please note that the output size of image is always the multiple of 16 depends on protocol of JPEG.

  Parameters:

    - decoder_engine -- [in] Handle of the JPEG decoder instance to use for processing.

    - decode_cfg -- [in] Config structure of decoder.

    - bit_stream -- [in] Pointer to the buffer containing the input JPEG image data.

    - stream_size -- [in] Size of the input JPEG image data in bytes.

    - decode_outbuf -- [in] Pointer to the buffer that will receive the decoded image data.

    - outbuf_size -- [in] The size of `decode_outbuf`

    - out_size -- [out] Pointer to a variable that will receive the length of the output image data.

  Returns:

    - ESP_OK: JPEG decoder process successfully.

    - ESP_ERR_INVALID_ARG: JPEG decoder process failed because of invalid argument.

esp_err_t jpeg_del_decoder_engine(jpeg_decoder_handle_t decoder_engine)

  Release resources used by a JPEG decoder instance.

  This function releases the resources used by the specified JPEG decoder instance. The decoder instance is specified by the `decoder_engine` parameter.

  Parameters:

    decoder_engine -- Handle of the JPEG decoder instance to release resources for.

  Returns:

    - ESP_OK: Delete JPEG decoder successfully.

    - ESP_ERR_INVALID_ARG: Delete JPEG decoder failed because of invalid argument.

void *jpeg_alloc_decoder_mem(size_t size, const jpeg_decode_memory_alloc_cfg_t *mem_cfg, size_t *allocated_size)

  A helper function to allocate memory space for JPEG decoder.

  Parameters:

    - size -- [in] The size of memory to allocate.

    - mem_cfg -- [in] Memory configuration for memory allocation

    - allocated_size -- [out] Actual allocated buffer size.

  Returns:

    Pointer to the allocated memory space, or NULL if allocation fails.

### Structures

struct jpeg_decode_cfg_t

  Configuration parameters for a JPEG decoder image process.

  Public Members

  jpeg_dec_output_format_t output_format

    JPEG decoder output format

  jpeg_dec_rgb_element_order_t rgb_order

    JPEG decoder output order

  jpeg_yuv_rgb_conv_std_t conv_std

    JPEG decoder yuv->rgb standard

struct jpeg_decode_engine_cfg_t

  Configuration parameters for the JPEG decoder engine.

  Public Members

  int intr_priority

    JPEG interrupt priority, if set to 0, driver will select the default priority (1,2,3).

  int timeout_ms

    JPEG timeout threshold for handling a picture, should larger than valid decode time in ms. For example, for 30fps decode, this value must larger than 34. -1 means wait forever

  uint32_t allow_pd

    If set, the driver will backup/restore the JPEG registers before/after entering/exist sleep mode. By this approach, the system can power off JPEG's power domain. This can save power, but at the expense of more RAM being consumed

  struct jpeg_decode_engine_cfg_t flags

    JPEG engine configuration flags

struct jpeg_decode_picture_info_t

  Structure for jpeg decode header.

  Public Members

  uint32_t width

    Number of pixels in the horizontal direction

  uint32_t height

    Number of pixels in the vertical direction

  jpeg_down_sampling_type_t sample_method

    compressed JPEG picture sampling method

struct jpeg_decode_memory_alloc_cfg_t

  JPEG decoder memory allocation config.

  Public Members

  jpeg_dec_buffer_alloc_direction_t buffer_direction

    Buffer direction for jpeg decoder memory allocation

### Header File

- components/esp_driver_jpeg/include/driver/jpeg_encode.h

- This header file can be included with:

  >     #include "driver/jpeg_encode.h"

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

  >     REQUIRES esp_driver_jpeg

  > or

  >     PRIV_REQUIRES esp_driver_jpeg

### Functions

esp_err_t jpeg_new_encoder_engine(const jpeg_encode_engine_cfg_t *enc_eng_cfg, jpeg_encoder_handle_t *ret_encoder)

  Allocate JPEG encoder.

  Parameters:

    - enc_eng_cfg -- [in] config for jpeg encoder

    - ret_encoder -- [out] handle for jpeg encoder

  Returns:

    - ESP_OK: JPEG encoder initialized successfully.

    - ESP_ERR_INVALID_ARG: JPEG encoder initialization failed because of invalid argument.

    - ESP_ERR_NO_MEM: Create JPEG encoder failed because of out of memory.

esp_err_t jpeg_encoder_process(jpeg_encoder_handle_t encoder_engine, const jpeg_encode_cfg_t *encode_cfg, const uint8_t *encode_inbuf, uint32_t inbuf_size, uint8_t *encode_outbuf, uint32_t outbuf_size, uint32_t *out_size)

  Process encoding of JPEG data using the specified encoder engine.

  This function processes the encoding of JPEG data using the provided encoder engine and configuration. It takes an input buffer containing the raw image data, performs encoding based on the configuration settings, and outputs the compressed bitstream.

  Parameters:

    - encoder_engine -- [in] Handle to the JPEG encoder engine to be used for encoding.

    - encode_cfg -- [in] Pointer to the configuration structure for the JPEG encoding process.

    - encode_inbuf -- [in] Pointer to the input buffer containing the raw image data.

    - inbuf_size -- [in] Size of the input buffer in bytes.

    - encode_outbuf -- [in] Pointer to the output buffer where the compressed bitstream will be stored.

    - outbuf_size -- [in] The size of output buffer.

    - out_size -- [out] Pointer to a variable where the size of the output bitstream will be stored.

  Returns:

    - ESP_OK: JPEG encoder process successfully.

    - ESP_ERR_INVALID_ARG: JPEG encoder process failed because of invalid argument.

    - ESP_ERR_TIMEOUT: JPEG encoder process timeout.

esp_err_t jpeg_del_encoder_engine(jpeg_encoder_handle_t encoder_engine)

  Release resources used by a JPEG encoder instance.

  This function releases the resources used by the specified JPEG encoder instance. The encoder instance is specified by the `encoder_engine` parameter.

  Parameters:

    encoder_engine -- [in] Handle of the JPEG encoder instance to release resources for.

  Returns:

    - ESP_OK: Delete JPEG encoder successfully.

    - ESP_ERR_INVALID_ARG: Delete JPEG encoder failed because of invalid argument.

void *jpeg_alloc_encoder_mem(size_t size, const jpeg_encode_memory_alloc_cfg_t *mem_cfg, size_t *allocated_size)

  A helper function to allocate memory space for JPEG encoder.

  Parameters:

    - size -- [in] The size of memory to allocate.

    - mem_cfg -- [in] Memory configuration for memory allocation

    - allocated_size -- [out] Actual allocated buffer size.

  Returns:

    Pointer to the allocated memory space, or NULL if allocation fails.

### Structures

struct jpeg_encode_cfg_t

  JPEG encoder configure structure.

  Public Members

  uint32_t height

    Number of pixels in the horizontal direction

  uint32_t width

    Number of pixels in the vertical direction

  jpeg_enc_input_format_t src_type

    Source type of raw image to be encoded, see `jpeg_enc_src_type_t`

  jpeg_down_sampling_type_t sub_sample

    JPEG subsampling method

  uint32_t image_quality

    JPEG compressing quality, value from 1-100, higher value means higher quality

  bool pixel_reverse

    Whether to reverse the input pixel order, for detailed pixel order please refer to TRM

struct jpeg_encode_engine_cfg_t

  Configuration parameters for the JPEG encode engine.

  Public Members

  int intr_priority

    JPEG interrupt priority, if set to 0, driver will select the default priority (1,2,3).

  int timeout_ms

    JPEG timeout threshold for handling a picture, should larger than valid encode time in ms. For example, for 30fps encode, this value must larger than 34. -1 means wait forever

  uint32_t allow_pd

    If set, the driver will backup/restore the JPEG registers before/after entering/exist sleep mode. By this approach, the system can power off JPEG's power domain. This can save power, but at the expense of more RAM being consumed

  struct jpeg_encode_engine_cfg_t flags

    JPEG engine configuration flags

struct jpeg_encode_memory_alloc_cfg_t

  JPEG encoder memory allocation config.

  Public Members

  jpeg_enc_buffer_alloc_direction_t buffer_direction

    Buffer direction for jpeg encoder memory allocation

### Header File

- components/esp_driver_jpeg/include/driver/jpeg_types.h

- This header file can be included with:

  >     #include "driver/jpeg_types.h"

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

  >     REQUIRES esp_driver_jpeg

  > or

  >     PRIV_REQUIRES esp_driver_jpeg

### Type Definitions

typedef struct jpeg_decoder_t *jpeg_decoder_handle_t

  Type of jpeg decoder handle.

typedef struct jpeg_encoder_t *jpeg_encoder_handle_t

  Type of jpeg encoder handle.

### Enumerations

enum jpeg_dec_output_format_t

  Enumeration for jpeg output format.

  Values:

  enumerator JPEG_DECODE_OUT_FORMAT_RGB888

    output RGB888 format

  enumerator JPEG_DECODE_OUT_FORMAT_RGB565

    output RGB565 format

  enumerator JPEG_DECODE_OUT_FORMAT_GRAY

    output the gray picture

  enumerator JPEG_DECODE_OUT_FORMAT_YUV444

    output yuv444 format

  enumerator JPEG_DECODE_OUT_FORMAT_YUV422

    output yuv422 format

  enumerator JPEG_DECODE_OUT_FORMAT_YUV420

    output yuv420 format

enum jpeg_yuv_rgb_conv_std_t

  Enumeration for YUV and RGB conversion standard.

  Values:

  enumerator JPEG_YUV_RGB_CONV_STD_BT601

    BT601

  enumerator JPEG_YUV_RGB_CONV_STD_BT709

    BT709

enum jpeg_dec_rgb_element_order_t

  Enumeration for jpeg big/small endian output.

  Values:

  enumerator JPEG_DEC_RGB_ELEMENT_ORDER_BGR

    Output the color component in small endian

  enumerator JPEG_DEC_RGB_ELEMENT_ORDER_RGB

    Output the color component in big endian

enum jpeg_dec_buffer_alloc_direction_t

  Enumeration for jpeg decoder alloc buffer direction.

  Values:

  enumerator JPEG_DEC_ALLOC_INPUT_BUFFER

    Alloc the picture input buffer, (compressed format in decoder)

  enumerator JPEG_DEC_ALLOC_OUTPUT_BUFFER

    Alloc the picture output buffer, (decompressed format in decoder)

enum jpeg_enc_input_format_t

  Enumeration for jpeg input format.

  Values:

  enumerator JPEG_ENCODE_IN_FORMAT_RGB888

    input RGB888 format

  enumerator JPEG_ENCODE_IN_FORMAT_RGB565

    input RGB565 format

  enumerator JPEG_ENCODE_IN_FORMAT_GRAY

    input GRAY format

  enumerator JPEG_ENCODE_IN_FORMAT_YUV422

    input YUV422 format

  enumerator JPEG_ENCODE_IN_FORMAT_YUV444

    input YUV444 format

  enumerator JPEG_ENCODE_IN_FORMAT_YUV420

    input YUV420 format

enum jpeg_enc_buffer_alloc_direction_t

  Enumeration for jpeg encoder alloc buffer direction.

  Values:

  enumerator JPEG_ENC_ALLOC_INPUT_BUFFER

    Alloc the picture input buffer, (decompressed format in encoder)

  enumerator JPEG_ENC_ALLOC_OUTPUT_BUFFER

    Alloc the picture output buffer, (compressed format in encoder)

### Header File

- components/esp_hal_jpeg/include/hal/jpeg_types.h

- This header file can be included with:

  >     #include "hal/jpeg_types.h"

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

  >     REQUIRES esp_hal_jpeg

  > or

  >     PRIV_REQUIRES esp_hal_jpeg

### Unions

union jpeg_huffman_table_info_t
  #include <jpeg_types.h>

  Structure for huffman information.

  Public Members

  uint8_t id

    Huffman table id.

  uint8_t type

    Huffman table type.

  struct jpeg_huffman_table_info_t
  uint8_t info

    Information of huffman table.

### Structures

struct jpeg_component_factor_t

  Structure for recording factor of component.

  Public Members

  uint32_t horizontal

    horizontal factor

  uint32_t vertical

    vertical factor

### Macros

JPEG_HUFFMAN_BITS_LEN_TABLE_LEN

JPEG_HUFFMAN_AC_VALUE_TABLE_LEN

JPEG_HUFFMAN_DC_VALUE_TABLE_LEN

JPEG_QUANTIZATION_TABLE_LEN

JPEG_COMPONENT_NUMBER_MAX

DHT_TC_NUM

DHT_TH_NUM

JPEG_DOWN_SAMPLING_NUM

### Enumerations

enum jpeg_codec_mode_t

  Enum for JPEG codec working mode.

  Values:

  enumerator JPEG_CODEC_ENCODER

    Encode mode.

  enumerator JPEG_CODEC_DECODER

    Decode mode.

enum jpeg_sample_mode_t

  Enum for JPEG sampling mode.

  Values:

  enumerator JPEG_SAMPLE_MODE_YUV444

    sample in YUV444

  enumerator JPEG_SAMPLE_MODE_YUV422

    sample in YUV422

  enumerator JPEG_SAMPLE_MODE_YUV420

    sample in YUV420

enum jpeg_down_sampling_type_t

  Enumeration for jpeg decoder sample methods.

  Values:

  enumerator JPEG_DOWN_SAMPLING_YUV444

    Sample by YUV444

  enumerator JPEG_DOWN_SAMPLING_YUV422

    Sample by YUV422

  enumerator JPEG_DOWN_SAMPLING_YUV420

    Sample by YUV420

  enumerator JPEG_DOWN_SAMPLING_GRAY

    Sample the gray picture

enum jpeg_enc_src_type_t

  JPEG encoder source formats.

  Values:

  enumerator JPEG_ENC_SRC_RGB888

    JPEG encoder source RGB888

  enumerator JPEG_ENC_SRC_YUV422

    JPEG encoder source YUV422

  enumerator JPEG_ENC_SRC_RGB565

    JPEG encoder source RGB565

  enumerator JPEG_ENC_SRC_YUV444

    JPEG encoder source YUV444

  enumerator JPEG_ENC_SRC_YUV420

    JPEG encoder source YUV420

  enumerator JPEG_ENC_SRC_GRAY

    JPEG encoder source GRAY

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