Documentation

PNGD

This section describes the API call sequence of PNGD, and sample code is also provided to help you better understand the process.

The PNG decoder (PNGD) decodes images in PNG format. For details about the PNGD functions and restrictions, see Functions and Restrictions.

API Call Sequence

If PNG image decoding is involved during app development, ensure that your app contains the code logic for such image decoding. For details about the API call sequence, see pyACL API Call Sequence.

Figure 1 PNG image decoding

The current system supports PNG image decoding and output of RGB and RGBA images. The key APIs are described as follows:

  1. Call acl.media.dvpp_create_channel_desc to create a channel description.
  2. Call acl.media.dvpp_create_channel to create a channel for image data processing.
  3. Before decoding PNG images, call acl.media.dvpp_malloc to allocate device buffers for storing the input or output data.

    Before allocating an output buffer, call acl.media.dvpp_png_predict_dec_size to predict the output allocation size required for the decoded image based on the size of the PNG image.

  4. Call the asynchronous API acl.media.dvpp_png_decode_async for decoding.

    Also call acl.rt.synchronize_stream to block the application until all tasks in the specified stream are complete.

  5. After the decoding is complete, call acl.media.dvpp_free to free the input and output buffers in a timely manner.
  6. Call acl.media.dvpp_destroy_channel to destroy the image data processing channel.

    Call acl.media.dvpp_destroy_channel_desc to destroy the channel description after the channel is destroyed.

Sample Code

After the API calls, add an exception handling branch and specify log printing of different levels (such as ERROR_LOG and INFO_LOG). The following is a code snippet of key steps only, which is not ready to use.

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import acl
# ......

# 1. Initialize pyACL.
ACL_CONFIG_PATH = "../src/acl.json"
ret = acl.init(ACL_CONFIG_PATH)

# 2. Allocate runtime resources.

# 3. Create the description of the data processing channel. dvpp_channel_desc is of type acldvppChannelDesc.
dvpp_channel_desc = acl.media.dvpp_create_channel_desc()

# 4. Create a data processing channel.
ret = acl.media.dvpp_create_channel(dvpp_channel_desc)

# 5. Allocate the input buffer.
pic_name = "../data/test_png_dec.png"
np_png = np.fromfile(pic_name, dtype=np.byte)
in_buffer_size = np_png.itemsize * np_png.size
bytes_data = np_png.tobytes()
np_png_ptr = acl.util.bytes_to_ptr(bytes_data)
in_dev_buffer, ret = acl.media.dvpp_malloc(in_buffer_size)
ACL_MEMCPY_HOST_TO_DEVICE = 1
ret = acl.rt.memcpy(in_dev_buffer, in_buffer_size, np_png_ptr, in_buffer_size,
    ACL_MEMCPY_HOST_TO_DEVICE)

# 6. Allocate a decoding output buffer.
PIXEL_FORMAT_RGB_888 = 12
out_buffer_size, ret = acl.media.dvpp_png_predict_dec_size(np_png_ptr, in_buffer_size,
    PIXEL_FORMAT_RGB_888)
out_dev_buffer, ret = acl.media.dvpp_malloc(out_buffer_size)

# 7. Create the description of the decoded image and set the attribute values.
output_desc = acl.media.dvpp_create_pic_desc()
width, height, components, ret = acl.media.dvpp_png_get_image_info(np_png_ptr, in_buffer_size)
ret = acl.media.dvpp_set_pic_desc_data(output_desc, out_dev_buffer)
ret = acl.media.dvpp_set_pic_desc_size(output_desc, out_buffer_size)
ret = acl.media.dvpp_set_pic_desc_format(output_desc, PIXEL_FORMAT_RGB_888)

# 8. Perform asynchronous decoding and call acl.rt.synchronize_stream to wait for the stream tasks to complete.
ret = acl.media.dvpp_png_decode_async(dvpp_channel_desc, in_dev_buffer, in_buffer_size,
    output_desc, stream)
ret = acl.rt.synchronize_stream(stream)

# 9. After the decoding is complete, destroy the allocations, including the description of the output image, output buffer, description of the channel as well as the channel.
ret = acl.media.dvpp_destroy_pic_desc(output_desc)
ret = acl.media.dvpp_free(in_dev_buffer)
ret = acl.media.dvpp_free(out_dev_buffer)
ret = acl.media.dvpp_destroy_channel(dvpp_channel_desc)
ret = acl.media.dvpp_destroy_channel_desc(dvpp_channel_desc)

# 10. Destroy runtime allocations.
# Deinitialize pyACL.
ret = acl.finalize()
# ....
Parent topic: Media Data Processing V1