High-throughput JPEG 2000 (Rec. ITU-T T.814 | ISO/IEC 15444-15) decoder
npm install openhtsrc/test/site for an example that fetches a codestream and decodes into a Canvas element.
HT.js is an ES6 module that exposes a single Decoder class:
js
import {Decoder} from "./HT.js"
`
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`js
Decoder(codestreamSize)
`
* codestreamSize is the size of the codestream in bytes that will be decoder. The codestream is not required to be complete.
A Decoder object must instantiated for each codestream to be decoded.
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`js
UInt8Array getCodestreamBuffer()
`
Returns a view to the codestream buffer, which the client must fill with the codestream, e.g.:
`js
let decoder = new Decoder(j2c_bytes.length);
const decoder_buffer = decoder.getCodestreamBuffer();
decoder_buffer.set(j2c_bytes);
`
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readHeader()
Parses the codestream header. Must be called before any method, other than getCodestreamBuffer() is called.
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Size getDecodedImageSize(int decompositionLevel)
Returns the decoded image size at decomposition level decompositionLevel. decompositionLevel = 0 means the full image resolution.
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Size startDecoding(int decompositionLevel, bool requestPlanar)
Starts the decoding process.
* decompositionLevel indicates that the decomposition level to which the image is decoded. decompositionLevel = 0 indicates that
the full image is decoded.
requestPlanar indicates whether successive calls to decodeLine output RRR..., GGG..., BBB..., RRR...,... or RGBRGBRGB...,
(false). requestPlanar must be true if the encoded image contains any downsampled components, and false if the
codestream uses a color transform.
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UInt32Array decodeLineAsUnsignedSamples()
Decodes a complete line of the image as a sequence of UInt32 values.
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int getDecodedComponentNumber()
Returns the index of the component last decoded by decodeLineAsUnsignedSamples(). Can only be called if requestPlanar is true.
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FrameInfo getImageInfo()
Returns information about the image.
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int getNumDecompositions()
Returns the number of decomposition levels available.
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bool isReversible()
Indicates whether the image coding was lossless.
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int getProgressionOrder()
Returns the progression order.
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Point getDownSample(int i)
Returns the horizontal and vertical downsampling factor for the ith component.
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Point getImageOffset()
Returns the image offset.
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bool isUsingColorTransform()
Indicates whether the codestream uses color transforms.
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bool isDownsamplingUsed()
Indicates whether any component of the codestream is downsampled.
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`cpp
struct Size {
uint32_t width;
uint32_t height;
}
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`cpp
struct FrameInfo {
uint16_t width;
uint16_t height;
uint8_t bitsPerSample;
uint8_t componentCount;
bool isSigned;
}
`
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`cpp
struct Point {
uint32_t x;
uint32_t y;
}
`
Development
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openHTJS uses docker to run emscripten.
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Clone the repository:
git clone --recursive https://github.com/sandflow/openhtjs.git
Build the distribution under dist:
npm run build
Build the demo web page to build/site`: