Retrieving image information with rocJPEG

Retrieving image information is done using rocJpegGetImageInfo().

RocJpegStatus rocJpegGetImageInfo(
  RocJpegHandle handle,
  RocJpegStreamHandle jpeg_stream_handle,
  uint8_t *num_components,
  RocJpegChromaSubsampling *subsampling,
  uint32_t *widths,
  uint32_t *heights);

rocJpegGetImageInfo() takes the RocJpegHandle and a RocJpegStreamHandle as inputs, and returns the subsampling, number of components, and widths and heights of the components. These are passed to the subsampling, num_components, and widths and heights output parameters.

The subsampling output parameter is a RocJpegChromaSubsampling enum.

typedef enum {
  ROCJPEG_CSS_444 = 0,
  ROCJPEG_CSS_440 = 1,
  ROCJPEG_CSS_422 = 2,
  ROCJPEG_CSS_420 = 3,
  ROCJPEG_CSS_411 = 4,
  ROCJPEG_CSS_400 = 5,
  ROCJPEG_CSS_UNKNOWN = -1
} RocJpegChromaSubsampling;

Its value is set to the chroma subsampling retrieved from the image.

For example:

// Get the image info
uint8_t num_components;
RocJpegChromaSubsampling subsampling;
uint32_t widths[ROCJPEG_MAX_COMPONENT] = {};
uint32_t heights[ROCJPEG_MAX_COMPONENT] = {};

status = rocJpegGetImageInfo(handle, rocjpeg_stream_handle, &num_components, &subsampling, widths, heights);
if (status != ROCJPEG_STATUS_SUCCESS) {
  std::cerr << "Failed to get image info with error code: " << rocJpegGetErrorName(status) << std::endl;
  rocJpegStreamDestroy(rocjpeg_stream_handle);
  rocJpegDestroy(handle);
  return EXIT_FAILURE;
}

rocJpegGetImageInfo() is thread safe.

Note

The VCN hardware-accelerated JPEG decoder in AMD GPUs only supports decoding JPEG images with ROCJPEG_CSS_444, ROCJPEG_CSS_440, ROCJPEG_CSS_422, ROCJPEG_CSS_420, and ROCJPEG_CSS_400 chroma subsampling.