Struct ViewingCondition 

pub struct ViewingCondition {
    pub acuity_ppd: f64,
    pub browser_dppx: Option<f64>,
    pub image_intrinsic_dppx: Option<f64>,
    pub ppd: Option<f64>,
}

Viewing condition for perceptual quality assessment.

Models how an image will be viewed, which affects whether compression artifacts will be perceptible.

Example

use codec_eval::ViewingCondition;

// Desktop viewing with 2x retina display showing a 2x srcset image
let condition = ViewingCondition::desktop()
    .with_browser_dppx(2.0)
    .with_image_intrinsic_dppx(2.0);

// The effective PPD accounts for the srcset ratio
let ppd = condition.effective_ppd();

Fields

acuity_ppd: f64

Viewer’s visual acuity in pixels per degree.

This is the baseline PPD for the display and viewing distance. Typical values:

• Desktop at arm’s length: ~40 PPD
• Laptop: ~60 PPD
• Smartphone held close: ~90+ PPD

browser_dppx: Option<f64>

Browser/OS device pixel ratio.

For retina/HiDPI displays, this is typically 2.0 or 3.0. For standard displays, this is 1.0.

image_intrinsic_dppx: Option<f64>

Image’s intrinsic pixels per CSS pixel.

For srcset images:

• A 1x image has intrinsic_dppx = 1.0
• A 2x image has intrinsic_dppx = 2.0

This affects the effective resolution at which the image is displayed.

ppd: Option<f64>

Override or computed PPD for this specific viewing.

If Some, this value is used directly instead of computing from the other fields.

Implementations

impl ViewingCondition

pub fn new(acuity_ppd: f64) -> Self

Create a new viewing condition with the given acuity PPD.

Arguments

• acuity_ppd - The viewer’s visual acuity in pixels per degree.

pub fn desktop() -> Self

Desktop viewing condition (acuity ~40 PPD).

Represents viewing a standard desktop monitor at arm’s length (approximately 24 inches / 60 cm).

pub fn laptop() -> Self

Laptop viewing condition (acuity ~60 PPD).

Represents viewing a laptop screen at a typical distance (approximately 18 inches / 45 cm).

pub fn smartphone() -> Self

Smartphone viewing condition (acuity ~90 PPD).

Represents viewing a smartphone held at reading distance (approximately 12 inches / 30 cm).

pub fn with_browser_dppx(self, dppx: f64) -> Self

Set the browser/OS device pixel ratio.

Arguments

• dppx - Device pixel ratio (e.g., 2.0 for retina).

pub fn with_image_intrinsic_dppx(self, dppx: f64) -> Self

Set the image’s intrinsic pixels per CSS pixel.

Arguments

• dppx - Intrinsic DPI ratio (e.g., 2.0 for a 2x srcset image).

pub fn with_ppd_override(self, ppd: f64) -> Self

Override the computed PPD with a specific value.

Arguments

• ppd - The PPD value to use.

pub fn effective_ppd(&self) -> f64

Compute the effective PPD for metric adjustment.

If ppd is set, returns that value directly. Otherwise, computes the effective PPD from the acuity and dppx values.

The formula is:

effective_ppd = acuity_ppd * (image_intrinsic_dppx / browser_dppx)

This accounts for how srcset images are scaled on HiDPI displays.

pub fn srcset_ratio(&self) -> f64

Compute the srcset ratio (intrinsic / browser).

• ratio < 1: Image is undersized, browser upscales
• ratio = 1: Native resolution
• ratio > 1: Image is oversized, browser downscales

pub fn simulation_params( &self, image_width: u32, image_height: u32, mode: SimulationMode, ) -> SimulationParams

Compute simulation parameters for a given image size.

Returns the scale factor to apply and the adjusted PPD for metrics.

Arguments

• image_width - Original image width in pixels
• image_height - Original image height in pixels
• mode - Simulation mode (accurate or downsample-only)

Example

use codec_eval::viewing::{ViewingCondition, SimulationMode};

let condition = ViewingCondition::desktop()
    .with_browser_dppx(2.0)
    .with_image_intrinsic_dppx(1.0); // undersized

let params = condition.simulation_params(1000, 800, SimulationMode::DownsampleOnly);
assert_eq!(params.scale_factor, 1.0); // No upscaling
assert!(params.adjusted_ppd < 40.0);  // Adjusted for missing upscale

Trait Implementations

impl Clone for ViewingCondition

fn clone(&self) -> ViewingCondition

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ViewingCondition

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

Formats the value using the given formatter.

impl Default for ViewingCondition

fn default() -> Self

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for ViewingCondition

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for ViewingCondition

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for ViewingCondition

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for ViewingCondition