Functions and Restrictions
Function Description
JPEG Decoder (JPEGD) implements .jpg, .jpeg, .JPG, and .JPEG image decoding.
- JPEGD supports image rotation during image decoding.
If the input stream contains orientation information (the orientation of the camera to the scene when the image is captured), JPEGD parses the orientation information during decoding and rotates the image by 90º, 180º, or 270º, or mirrors the image. The width stride, height stride, and output buffer of the rotated image must meet the restrictions described in Restrictions on Image Formats, Width and Height Alignment, and Buffers.
If the stream of the input image is abnormal, JPEGD fails to read the orientation information. As a result, the image rotation function cannot be implemented.
For the following product versions, there are restrictions on image rotation:Model
Restriction
Atlas 200/300/500 Inference Product When multiple channels of large-resolution (for example, 3840 x 2160 or higher) JPEG images with rotation information are concurrently decoded, the image decoding may take a long time. As a result, the user process exits due to timeout.
- JPEGD supports retaining the source image format during image decoding.
The image encoding formats before and after decoding remain consistent. For example, if the source format is JPEG(440), the destination format is YUV440SP with V component before U component or YUV440SP with U component before V component.
Use the source image format for decoding in either of the following ways:
- Call acldvppJpegGetImageInfoV2 to obtain the source image format before JPEGD decoding. In the JPEGD decoding API call, set the format of the output image to be the same as that of the input image.
- In the JPEGD decoding API call, set the output format to PIXEL_FORMAT_UNKNOWN to get a semi-planar output in the source format with V component before U component. For example, if the source format is JPEG(440) and the destination format is set to PIXEL_FORMAT_UNKNOWN, the JPEGD destination format is YUV440SP with V component before U component.
If the JPEGD destination image will be fed to a model for inference, you are advised to set the output image format to PIXEL_FORMAT_UNKNOWN. In this case, JPEGD decodes with the source format preserved (ensure that the JPEGD destination format is supported by the model) to avoid inference accuracy drop.
If the JPEGD destination image will be used as the input of VPC, to decode with the source format preserved, check that VPC supports the JPEGD destination format by referring to Restrictions. If VPC does not support the JPEGD destination format, reconfigure a JPEGD destination format that is also supported by VPC.
Resolution Restrictions
- Input resolution range:
Model
Resolution Range
Atlas 200/300/500 Inference Product Atlas Training Series Product 32 x 32 to 8192 x 8192
- Output resolution range:
JPEGD only decodes images and does not change the image resolution. Therefore, the resolution of the output image is the same as that of the input image.
Restrictions on Image Formats, Width and Height Alignment, and Buffers
During JPEGD image decoding, acldvppMalloc and acldvppFree are called to allocate and free the input and output buffers on the device. The buffer lifetime is managed by the user.
- The size of the input buffer is the size of space occupied by the input image.
- The size of the output buffer can be predicted by calling acldvppJpegPredictDecSize. For details about the calculation formula, see the following table.
JPEGD supports only Huffman coding and does not support arithmetic encoding, progressive JPEG format, or JPEG 2000 format. The color space of the input image must be YUV with YUV components in the ratio of 4:4:4, 4:2:2, 4:2:0, 4:0:0, or 4:4:0.
For details about the definition of the output image format, see acldvppPixelFormat. For details about the concepts such as width stride and height stride, see Terminology.
Input Format (YUV) |
Output Format |
Output Width and Height |
Output Width Stride, Height Stride, and Buffer Size |
|---|---|---|---|
JPEG(444) |
YVU444SP 8-bit |
No alignment requirement. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 3 |
YUV444SP 8-bit |
|||
YUV420SP NV12 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 3/2 |
|
YUV420SP NV21 8-bit |
|||
JPEG(422) |
YVU422SP 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 2 |
YUV422SP 8-bit |
|||
YUV420SP NV12 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 3/2 |
|
YUV420SP NV21 8-bit |
|||
JPEG(420) |
YUV420SP NV12 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 3/2 |
YUV420SP NV21 8-bit |
|||
JPEG(400) |
YUV420SP NV12 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 3/2 |
YUV420SP NV21 8-bit |
|||
YUV400 8-bit The |
No alignment requirement. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 2 |
|
JPEG(440) |
YVU440SP 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 2 |
YUV440SP 8-bit |
|||
YUV420SP NV12 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Width stride: Round up the width to the nearest multiple of 128. Height stride: Round up the height to the nearest multiple of 16. Buffer size (in bytes) ≥ Width stride x Height stride x 3/2 |
|
YUV420SP NV21 8-bit |
Requirements for Software and Hardware
- Hardware requirements
- A maximum of four Huffman tables are supported, including two direct coefficient (DC) tables and two alternating coefficient (AC) tables.
- A maximum of three quantization tables are supported.
- Only 8-bit sampling is supported.
- Only sequentially-encoded images can be decoded.
- Only JPEG decoding based on discrete cosine transform (DCT) is supported.
- Only one start of scan (SOS) marker is allowed for image decoding.
- Software requirements
- A maximum of three SOS markers are allowed for image decoding.
- Decoding of abnormal images with insufficient data in minimum coded units (MCUs) is supported.
Accuracy Restrictions
Ascend 310 AI Processor and Ascend 910 AI Processor: In the event of JPEGD+VPC cascade, widthStride x heightStride of the JPEGD output image must be a multiple of 128 x 16, so there are some invalid paddings. Therefore, when executing VPC functions such as resizing, call the acldvppSetPicDescWidth and acldvppSetPicDescHeight APIs to set the original width and height of the input image. As such, VPC will automatically crop the image based on the width and height of the source image and then resize the image, eliminating the impact of invalid data on image accuracy.