Enum Scale 

#[non_exhaustive]
pub enum Scale {
    Eighth,
    Quarter,
    Half,
    Full,
}

How much of an image a decode produces, as eighths of full size.

What it buys

A downsampled block can be produced directly from its coefficients, so a thumbnail never materializes the full-resolution image for the rest of the pipeline to carry: at 1/8 the resize, colour conversion and every later op see one sixty-fourth of the pixels. The reduced transform is also cheaper than the full one at 1/8 and 1/4, though at 1/2 it is not — it folds all sixty-four coefficients into sixteen outputs. The saving that matters is downstream, not in the transform.

This is a resolution reduction, not random access: rows still arrive top to bottom, and every coefficient is still entropy-decoded. A scaled decode is therefore a decoder configuration rather than a DecodeCapability.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Eighth

1/8 scale: the DC coefficient alone.

Quarter

1/4 scale.

Half

1/2 scale.

Full

Full resolution.

Implementations

impl Scale

pub const ALL: [Scale; 4]

Every scale, coarsest first.

pub const fn block_size(self) -> u32

The side of the block this scale produces, in samples: M of M/8.

pub const fn apply(self, source: u32) -> u32

The size source decodes to at this scale.

Rounded up, as the format requires: an image 61 pixels wide is 8 blocks across, and at 1/8 scale those 8 blocks are 8 samples.

pub fn fitting(source: (u32, u32), target: (u32, u32)) -> Scale

The coarsest scale still at least target in both axes.

Never returns a scale that would decode below the target: enlarging afterwards would throw away detail and then invent it back, which is worse than decoding one step larger and shrinking properly.

Trait Implementations

impl Clone for Scale

fn clone(&self) -> Scale

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Scale

impl Debug for Scale

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

Formats the value using the given formatter.

impl Default for Scale

fn default() -> Scale

Returns the “default value” for a type.

impl Eq for Scale

impl Ord for Scale

fn cmp(&self, other: &Scale) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl PartialEq for Scale

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

Equality operator ==.

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

Inequality operator !=.

impl PartialOrd for Scale

fn partial_cmp(&self, other: &Scale) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

Tests less than (for self and other) and is used by the < operator.

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

Tests less than or equal to (for self and other) and is used by the <= operator.

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

Tests greater than (for self and other) and is used by the > operator.

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

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for Scale