Struct JpegDecoder

pub struct JpegDecoder<T: ZReaderTrait> {

    pub(crate) info: ImageInfo,
    pub(crate) qt_tables: [Option<[i32; 64]>; 4],
    pub(crate) dc_huffman_tables: [Option<HuffmanTable>; 4],
    pub(crate) ac_huffman_tables: [Option<HuffmanTable>; 4],
    pub(crate) components: Vec<Components>,
    pub(crate) h_max: usize,
    pub(crate) v_max: usize,
    pub(crate) mcu_width: usize,
    pub(crate) mcu_height: usize,
    pub(crate) mcu_x: usize,
    pub(crate) mcu_y: usize,
    pub(crate) is_interleaved: bool,
    pub(crate) sub_sample_ratio: SampleRatios,
    pub(crate) input_colorspace: ColorSpace,
    pub(crate) is_progressive: bool,
    pub(crate) spec_start: u8,
    pub(crate) spec_end: u8,
    pub(crate) succ_high: u8,
    pub(crate) succ_low: u8,
    pub(crate) num_scans: u8,
    pub(crate) idct_func: fn(&mut [i32; 64], &mut [i16], usize),
    pub(crate) color_convert_16: fn(&[i16; 16], &[i16; 16], &[i16; 16], &mut [u8], &mut usize),
    pub(crate) z_order: [usize; 4],
    pub(crate) restart_interval: usize,
    pub(crate) todo: usize,
    pub(crate) options: DecoderOptions,
    pub(crate) stream: ZByteReader<T>,
    pub(crate) headers_decoded: bool,
    pub(crate) seen_sof: bool,
    pub(crate) exif_data: Option<Vec<u8>>,
    pub(crate) icc_data: Vec<ICCChunk>,
    pub(crate) is_mjpeg: bool,
    pub(crate) coeff: usize,
}

A JPEG Decoder Instance.

Fields

info: ImageInfo

Struct to hold image information from SOI

qt_tables: [Option<[i32; 64]>; 4]

Quantization tables, will be set to none and the tables will be moved to components field

dc_huffman_tables: [Option<HuffmanTable>; 4]

DC Huffman Tables with a maximum of 4 tables for each component

ac_huffman_tables: [Option<HuffmanTable>; 4]

AC Huffman Tables with a maximum of 4 tables for each component

components: Vec<Components>

Image components, holds information like DC prediction and quantization tables of a component

h_max: usize

maximum horizontal component of all channels in the image

v_max: usize

mcu_width: usize

mcu’s width (interleaved scans)

mcu_height: usize

MCU height(interleaved scans

mcu_x: usize

Number of MCU’s in the x plane

mcu_y: usize

Number of MCU’s in the y plane

is_interleaved: bool

Is the image interleaved?

sub_sample_ratio: SampleRatios

input_colorspace: ColorSpace

Image input colorspace, should be YCbCr for a sane image, might be grayscale too

is_progressive: bool

Is the image progressive?

spec_start: u8

Start of spectral scan

spec_end: u8

End of spectral scan

succ_high: u8

Successive approximation bit position high

succ_low: u8

Successive approximation bit position low

num_scans: u8

Number of components.

idct_func: fn(&mut [i32; 64], &mut [i16], usize)

Dequantize and idct function

color_convert_16: fn(&[i16; 16], &[i16; 16], &[i16; 16], &mut [u8], &mut usize)

z_order: [usize; 4]

restart_interval: usize

restart markers

todo: usize

options: DecoderOptions

stream: ZByteReader<T>

headers_decoded: bool

seen_sof: bool

exif_data: Option<Vec<u8>>

icc_data: Vec<ICCChunk>

is_mjpeg: bool

coeff: usize

Implementations

impl<T> JpegDecoder<T>

where T: ZReaderTrait,

fn default(options: DecoderOptions, buffer: T) -> Self

pub fn decode(&mut self) -> Result<Vec<u8>, DecodeErrors>

Decode a buffer already in memory

The buffer should be a valid jpeg file, perhaps created by the command std:::fs::read() or a JPEG file downloaded from the internet.

Errors

See DecodeErrors for an explanation

pub fn new(stream: T) -> JpegDecoder<T>

Create a new Decoder instance

Arguments

• stream: The raw bytes of a jpeg file.

pub fn info(&self) -> Option<ImageInfo>

Returns the image information

This must be called after a subsequent call to decode or decode_headers it will return None

Returns

• Some(info): Image information,width, height, number of components
• None: Indicates image headers haven’t been decoded

pub fn output_buffer_size(&self) -> Option<usize>

Return the number of bytes required to hold a decoded image frame decoded using the given input transformations

Returns

• Some(usize): Minimum size for a buffer needed to decode the image
• None: Indicates the image was not decoded, or image dimensions would overflow a usize

pub const fn get_options(&self) -> &DecoderOptions

Get a mutable reference to the decoder options for the decoder instance

This can be used to modify options before actual decoding but after initial creation

Example

use zune_jpeg::JpegDecoder;

let mut decoder = JpegDecoder::new(&[]);
// get current options
let mut options = decoder.get_options();
// modify it
 let new_options = options.set_max_width(10);
// set it back
decoder.set_options(new_options);

pub fn get_input_colorspace(&self) -> Option<ColorSpace>

Return the input colorspace of the image

This indicates the colorspace that is present in the image, but this may be different to the colorspace that the output will be transformed to

Returns

-Some(Colorspace): Input colorspace

• None : Indicates the headers weren’t decoded

pub fn set_options(&mut self, options: DecoderOptions)

Set decoder options

This can be used to set new options even after initialization but before decoding.

This does not bear any significance after decoding an image

Arguments

• options: New decoder options

Example

Set maximum jpeg progressive passes to be 4

use zune_jpeg::JpegDecoder;
let mut decoder =JpegDecoder::new(&[]);
// this works also because DecoderOptions implements `Copy`
let options = decoder.get_options().jpeg_set_max_scans(4);
// set the new options
decoder.set_options(options);
// now decode
decoder.decode().unwrap();

fn decode_headers_internal(&mut self) -> Result<(), DecodeErrors>

Decode Decoder headers

This routine takes care of parsing supported headers from a Decoder image

Supported Headers

• APP(0)
• SOF(O)
• DQT -> Quantization tables
• DHT -> Huffman tables
• SOS -> Start of Scan

Unsupported Headers

• SOF(n) -> Decoder images which are not baseline/progressive
• DAC -> Images using Arithmetic tables
• JPG(n)

pub(crate) fn parse_marker_inner( &mut self, m: Marker, ) -> Result<(), DecodeErrors>

pub fn icc_profile(&self) -> Option<Vec<u8>>

Get the embedded ICC profile if it exists and is correct

One needs not to decode the whole image to extract this, calling decode_headers for an image with an ICC profile allows you to decode this

Returns

• Some(Vec<u8>): The raw ICC profile of the image
• None: May indicate an error in the ICC profile , non-existence of an ICC profile, or that the headers weren’t decoded.

pub fn exif(&self) -> Option<&Vec<u8>>

Return the exif data for the file

This returns the raw exif data starting at the TIFF header

Returns

-Some(data): The raw exif data, if present in the image

• None: May indicate the following

  1. The image doesn’t have exif data
  2. The image headers haven’t been decoded

pub fn get_output_colorspace(&self) -> Option<ColorSpace>

Get the output colorspace the image pixels will be decoded into

Note.

This field can only be regarded after decoding headers, as markers such as Adobe APP14 may dictate different colorspaces than requested.

Calling decode_headers is sufficient to know what colorspace the output is, if this is called after decode it indicates the colorspace the output is currently in

Additionally not all input->output colorspace mappings are supported but all input colorspaces can map to RGB colorspace, so that’s a safe bet if one is handling image formats

Returns

• Some(Colorspace): If headers have been decoded, the colorspace the output array will be in
• `None

pub fn decode_into(&mut self, out: &mut [u8]) -> Result<(), DecodeErrors>

Decode into a pre-allocated buffer

It is an error if the buffer size is smaller than output_buffer_size()

If the buffer is bigger than expected, we ignore the end padding bytes

Example

• Read headers and then alloc a buffer big enough to hold the image

use zune_jpeg::JpegDecoder;
let mut decoder = JpegDecoder::new(&[]);
// before we get output, we must decode the headers to get width
// height, and input colorspace
decoder.decode_headers().unwrap();

let mut out = vec![0;decoder.output_buffer_size().unwrap()];
// write into out
decoder.decode_into(&mut out).unwrap();

pub fn decode_headers(&mut self) -> Result<(), DecodeErrors>

Read only headers from a jpeg image buffer

This allows you to extract important information like image width and height without decoding the full image

Examples

use zune_jpeg::{JpegDecoder};

let img_data = std::fs::read("a_valid.jpeg").unwrap();
let mut decoder = JpegDecoder::new(&img_data);
decoder.decode_headers().unwrap();

println!("Total decoder dimensions are : {:?} pixels",decoder.dimensions());
println!("Number of components in the image are {}", decoder.info().unwrap().components);

Errors

See DecodeErrors enum for list of possible errors during decoding

pub fn new_with_options(buf: T, options: DecoderOptions) -> JpegDecoder<T>

Create a new decoder with the specified options to be used for decoding an image

Arguments

• buf: The input buffer from where we will pull in compressed jpeg bytes from
• options: Options specific to this decoder instance

pub(crate) fn set_upsampling(&mut self) -> Result<(), DecodeErrors>

Set up-sampling routines in case an image is down sampled

pub(crate) fn width(&self) -> u16

Get the width of the image as a u16

The width lies between 1 and 65535

pub(crate) fn height(&self) -> u16

Get the height of the image as a u16

The height lies between 1 and 65535

pub const fn dimensions(&self) -> Option<(usize, usize)>

Get image dimensions as a tuple of width and height or None if the image hasn’t been decoded.

Returns

• Some(width,height): Image dimensions
• None : The image headers haven’t been decoded

impl<T: ZReaderTrait> JpegDecoder<T>

pub(crate) fn check_tables(&self) -> Result<(), DecodeErrors>

Check for existence of DC and AC Huffman Tables

pub(crate) fn decode_mcu_ycbcr_baseline( &mut self, pixels: &mut [u8], ) -> Result<(), DecodeErrors>

Decode MCUs and carry out post processing.

This is the main decoder loop for the library, the hot path.

Because of this, we pull in some very crazy optimization tricks hence readability is a pinch here.

pub(crate) fn finish_baseline_decoding( &mut self, block: &[Vec<i16>; 4], _mcu_width: usize, pixels: &mut [u8], ) -> Result<(), DecodeErrors>

Process all MCUs when baseline decoding has been processing them component-after-component. For simplicity this assembles the dequantized blocks in the order that the post processing of an interleaved baseline decoding would use.

fn decode_mcu_width<const PROGRESSIVE: bool>( &mut self, mcu_width: usize, mcu_height: usize, tmp: &mut [i32; 64], stream: &mut BitStream, progressive: &mut [Vec<i16>; 4], ) -> Result<McuContinuation, DecodeErrors>

pub(crate) fn handle_rst( &mut self, stream: &mut BitStream, ) -> Result<(), DecodeErrors>

pub(crate) fn post_process( &mut self, pixels: &mut [u8], i: usize, mcu_height: usize, width: usize, padded_width: usize, pixels_written: &mut usize, upsampler_scratch_space: &mut [i16], ) -> Result<(), DecodeErrors>

impl<T: ZReaderTrait> JpegDecoder<T>

pub(crate) fn decode_mcu_ycbcr_progressive( &mut self, pixels: &mut [u8], ) -> Result<(), DecodeErrors>

Decode a progressive image

This routine decodes a progressive image, stopping if it finds any error.

fn reset_prog_params(&mut self, stream: &mut BitStream)

Reset progressive parameters

fn parse_entropy_coded_data( &mut self, stream: &mut BitStream, buffer: &mut [Vec<i16>; 4], ) -> Result<(), DecodeErrors>

pub(crate) fn handle_rst_main( &mut self, stream: &mut BitStream, ) -> Result<(), DecodeErrors>

fn finish_progressive_decoding( &mut self, block: &[Vec<i16>; 4], _mcu_width: usize, pixels: &mut [u8], ) -> Result<(), DecodeErrors>

pub(crate) fn reset_params(&mut self)