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 product models below, if the height of the original image is an odd number and the rotation is to swap the width and height, black borders will exist in the odd borders after rotation. In this case, align the odd borders downwards to an even number (to remove the black borders). Take a JPEGD 422 image as an example. If the original size is 200 × 101 and the size after rotation is 101 × 200, the actual region should be 100 × 200. Take a JPEGD 440 image as an example, if the original size is 201 × 101 and the size after rotation is 100 × 201, the actual region should be 100 × 200.Ascend 950PR /Ascend 950DT Atlas A3 training products /Atlas A3 inference products Atlas A2 training products /Atlas A2 inference products Atlas 200I/500 A2 inference products
- 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.
Resolution Restrictions
Model |
Resolution Range |
|---|---|
32 × 32 to 8192 × 8192 |
|
32 × 32 to 16384 × 16384 |
Output image 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
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.
The table below lists the output image formats supported by JPEGD. For details about the definitions of the output image formats, see acldvppPixelFormat.
The alignment restrictions on width stride × height stride vary according to the product. For details about the concepts such as width stride and height stride, see Terminology.
- Width stride × height stride must be a multiple of 64 × 16 on the following products:
Atlas A3 training products /Atlas A3 inference products Atlas A2 training products /Atlas A2 inference products Atlas 200I/500 A2 inference products Atlas inference products - Width stride × height stride must be a multiple of 128 × 16 on the following products:
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 output buffer size refers to the size of the buffer used for storing the output image. You can call acldvppJpegPredictDecSize to estimate the size. The following table lists the calculation formulas.
Input Format (YUV) |
Output Format |
Output Width and Height Alignment |
Output Buffer Size |
|---|---|---|---|
JPEG(444) |
YVU444SP 8-bit YUV444SP 8-bit |
No alignment requirement. |
Buffer size (in bytes) ≥ Width stride × Height stride × 3 |
JPEG(444) |
YUV420SP NV12 8-bit YUV420SP NV21 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Buffer size (in bytes) ≥ Width stride × Height stride × 3/2 |
JPEG(422) |
YVU422SP 8-bit YUV422SP 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Buffer size (in bytes) ≥ Width stride × Height stride × 2 |
JPEG(422) |
YUV420SP NV12 8-bit YUV420SP NV21 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Buffer size (in bytes) ≥ Width stride × Height stride × 3/2 |
JPEG(420) |
YUV420SP NV12 8-bit YUV420SP NV21 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Buffer size (in bytes) ≥ Width stride × Height stride × 3/2 |
JPEG(400) |
YUV420SP NV12 8-bit YUV420SP NV21 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Buffer size (in bytes) ≥ Width stride × Height stride × 3/2 |
JPEG(400) |
YUV400 8-bit |
No alignment requirement. |
Buffer size (in bytes) ≥ Width stride × Height stride |
JPEG(440) |
YVU440SP 8-bit YUV440SP 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Buffer size (in bytes) ≥ Width stride × Height stride × 2 |
JPEG(440) |
YUV420SP NV12 8-bit YUV420SP NV21 8-bit |
Width: Must be a multiple of 2. Height: Must be a multiple of 2. |
Buffer size (in bytes) ≥ Width stride × Height stride × 3/2 |
Note: If the JPEGD destination image will be used as the input of VPC, to decode with the source format preserved, check whether VPC supports the JPEGD destination format by referring to VPC Restrictions. If VPC does not support the JPEGD destination format, reconfigure a JPEGD destination format that is also supported by VPC.
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
In the event of JPEGD+VPC cascade, width stride × height stride of the JPEGD output image has alignment restrictions, so there are some invalid paddings. Therefore, when executing VPC functions such as resizing, call acldvppSetPicDescWidth and acldvppSetPicDescHeight to correctly 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 before resizing the image, eliminating the impact of invalid data on image accuracy.