Struct JpegDecoder 

pub struct JpegDecoder<S>
where
    S: Source,
{ /* private fields */ }

Decodes a JPEG stream.

Baseline frames stream one MCU row at a time. Progressive frames decode their scans into a coefficient buffer first and are then served the same way; the distinction is not visible through Decoder.

Implementations

impl<S> JpegDecoder<S>

where S: Source,

pub fn new(source: S, limits: Limits) -> Result<JpegDecoder<S>, PixelsError>

Read every header up to and including the scan header.

No coefficient is decoded here, baseline or progressive, so this is the probe()/metadata path as well as the start of a decode (SPEC §Guarantees 3).

Errors

Returns PixelsError::Malformed for a stream that is not a well-formed JPEG, PixelsError::Unsupported for a variant this crate does not handle (arithmetic coding, lossless, 12-bit, CMYK), or PixelsError::LimitExceeded if the frame exceeds limits.

pub fn with_scale( source: S, limits: Limits, scale: Scale, ) -> Result<JpegDecoder<S>, PixelsError>

Read every header, and decode at a reduced resolution.

At M/8 scale the decoder inverse-transforms only the low-frequency corner of each block, so a thumbnail costs a fraction of the arithmetic and — the point of it — the full-resolution image is never materialized. Entropy decoding is unchanged: every coefficient is still read, because the format gives no way to skip one.

Decoder::descriptor reports the scaled size, so a caller that asks for a reduced decode is told what it will actually receive.

Errors

As JpegDecoder::new.

pub const fn scale(&self) -> Scale

The resolution this decoder produces, as eighths of full size.

pub const fn is_progressive(&self) -> bool

Whether this stream is a progressive frame.

Trait Implementations

impl<S> Debug for JpegDecoder<S>

where S: Debug + Source,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<S> Decoder for JpegDecoder<S>

where S: Source + Debug,

fn icc_profile(&self) -> Option<&[u8]>

The ICC profile, joined from its APP2 segments.

fn exif(&self) -> Option<&[u8]>

The EXIF block, from the first EXIF APP1 segment.

fn xmp(&self) -> Option<&[u8]>

The XMP packet, from the first XMP APP1 segment. The extended XMP a packet over 64 KB spills into is not joined.

fn source_info(&self) -> SourceInfo

Progressive, chroma subsampling, density (JFIF, else EXIF) and COM comments before the first scan.

fn orientation(&self) -> Orientation

The EXIF orientation, from the first EXIF APP1 segment.

fn descriptor(&self) -> ImageDescriptor

The shape of the image, known after the header is parsed.

fn capability(&self) -> DecodeCapability

What this decoder can produce without a full decode.

fn reduced_descriptor(&self, target: (u32, u32)) -> Option<ImageDescriptor>

What this decoder would produce if asked for target or larger, when the format lets it reach that size more cheaply than a full decode.

fn reduce_to(&mut self, descriptor: ImageDescriptor) -> Result<(), PixelsError>

Commit to producing descriptor, which Decoder::reduced_descriptor must have returned.

fn read_row(&mut self, out: &mut [u8]) -> Result<(), PixelsError>

Decode the next row, top to bottom, into out.

fn animation(&self) -> Option<Animation>

The source’s animation, if it has more than one frame.

fn pages(&self) -> u32

How many pages the source document holds, at least 1.

fn read_region( &mut self, region: Region, out: &mut TileMut<'_>, ) -> Result<(), PixelsError>

Decode an arbitrary region into out.