JPEG Codec¶

Version: 1.0
URI: https://awslabs.github.io/osml-imagery-io/codecs/jpeg
Codec type: array-to-bytes

Decodes JPEG DCT streams into NumPy arrays. Handles interleave conversion and color space transformation, producing band-sequential output regardless of the input interleave mode.

This codec is format-agnostic — it decodes any valid JPEG stream regardless of the source container format.

Document Conventions¶

The key words “MUST”, “MUST NOT”, “SHOULD”, and “MAY” in this document are to be interpreted as described in RFC 2119.

Codec Identifier¶

The value of the name member in the codec metadata MUST be https://awslabs.github.io/osml-imagery-io/codecs/jpeg.

Encoded Representation¶

The encoded representation MUST be a valid JPEG interchange format (JFIF) byte sequence conforming to ITU-T T.81. The stream begins with an SOI marker (0xFFD8) and ends with an EOI marker (0xFFD9).

The JPEG data MAY use 8-bit or 12-bit sample precision as indicated by the bits_per_pixel configuration parameter.

Configuration Parameters¶

Field	Type	Required	Description
`bits_per_pixel`	`int`	Yes	Bits per pixel: `8` or `12`.
`num_bands`	`int`	Yes	Number of bands (`1` for mono, `3` for RGB/YCbCr).
`block_width`	`int`	Yes	Block width in pixels.
`block_height`	`int`	Yes	Block height in pixels.
`imode`	`string`	Yes	Interleave mode: `"B"` (band interleaved by block), `"P"` (pixel interleaved), `"R"` (row interleaved), or `"S"` (band sequential).
`color_space`	`string`	Yes	JPEG color space: `"MONO"`, `"RGB"`, or `"YCbCr601"`.

Algorithm¶

Decoding¶

Decode the JPEG stream using the specified color_space and bits_per_pixel.
Convert the decoded pixels from the input imode to band-sequential (BSQ) format.
Return an array with shape (num_bands, block_height, block_width) and uint8 dtype (or uint16 for 12-bit).

Encoding¶

Encoding is not currently specified. See Implementation Notes.

Example Configuration¶

{
    "name": "https://awslabs.github.io/osml-imagery-io/codecs/jpeg",
    "configuration": {
        "bits_per_pixel": 8,
        "num_bands": 3,
        "block_width": 256,
        "block_height": 256,
        "imode": "P",
        "color_space": "YCbCr601"
    }
}

References¶

ITU-T T.81 — Digital compression and coding of continuous-tone still images (JPEG)
RFC 2119 — Key words for use in RFCs to Indicate Requirement Levels

Implementation Notes¶

aws.osml.io.zarr_codecs.JpegCodec — see API Reference.

Only the decode path is implemented. Calling encode() raises NotImplementedError.