Enum Compression 

pub enum Compression {
    Rice,
    Gzip,
    ShuffledGzip,
    Hcompress {
        scale: i64,
    },
    Plio,
    None,
}

Which algorithm the tiles are compressed with.

The convention defines several, and they suit different data. Rice is the usual choice for astronomical images: it is fast and, on data where each pixel is close to the one before it, it is the smallest of these. Gzip compresses anything at all, including floating point values that have not been quantised, which is what makes it the one lossless choice for a floating point image.

Variants

Rice

RICE_1: the differences between neighbouring pixels, coded so that small ones are short. Integers only — a floating point image has to be quantised first.

Gzip

GZIP_1: deflate over the tile’s bytes as they stand.

ShuffledGzip

GZIP_2: deflate after gathering the first byte of every value, then the second, and so on, which usually compresses better because the high bytes of neighbouring values are alike.

Hcompress

HCOMPRESS_1: an image transform that gathers each two by two block into a sum and three differences, coded as a quadtree. It compresses smooth images better than Rice, and at a scale above one it does so by throwing away the low bits of each coefficient — which is lossy, and which ImageHDU::read_image can smooth back over.

A scale of zero or one keeps every bit. Tiles are two-dimensional, so this cannot be used with a tile that reaches along a third axis.

Fields

scale: i64

What the transform’s coefficients are divided by.

Plio

PLIO_1: run-length coding for the integer masks IRAF writes, where a tile is mostly long runs of the same small number. Values must be non-negative and no wider than twenty-seven bits.

None

NOCOMPRESS: the tiles are stored as they are. Useful for writing a file in the tiled layout without paying to compress it.

Implementations

impl Compression

pub fn card_value(self) -> &'static str

The name a ZCMPTYPE card writes this algorithm under.

Trait Implementations

impl Clone for Compression

fn clone(&self) -> Compression

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Compression

impl Debug for Compression

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

Formats the value using the given formatter.

impl Default for Compression

fn default() -> Compression

Returns the “default value” for a type.

impl Eq for Compression

impl PartialEq for Compression

fn eq(&self, other: &Compression) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Compression