Repository: GoogleChrome/lighthouse (js)

Issue:
uses-responsive-images only cares about savings not about correct use of responsive images
The `uses-responsive-images` check only checks whether a too large image is used. This means that it only catches cases in which the used image is way bigger than the actual display size. This typically happens when developers just shove a @2x or larger version of the image without using a `srcset`.

The part that is missing is when the image is too small compared to the display size. I.e, no @2x version is in use.

Basically I'm suggesting to add something along the lines:

```js
const DPR = artifacts.ViewportDimensions.devicePixelRatio;
const TOLERANCE = 0.9; // This is to not produce that many violations, I'd like it to be set to 1.
const bigEnough = image.displayedHeight <= image.naturalHeight / (DPR * TOLERANCE) && image.displayedWidth <= image.naturalWidth / (DPR * TOLERANCE);
```

I understand, that doing in that way may change the scope of the audit, as it is currently part of the byte efficiency category. So feel free to recategorize this as a feature request.

Pull request description:
new_audit: check images are big enough
**Summary**
New audit checking visible images are big enough. This is a complement to `UsesResponsiveImages`.

**Related Issues/PRs**
Fixes #10434. Check that issue for the New Audit Proposal.

Patch:
diff --git a/AUTHORS b/AUTHORS
index 158b3741a..6b230b136 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -5,4 +5,5 @@
 # To see the full list of contributors, see the revision history in
 # source control.
 Google LLC
+Sebastian Kreft
 
diff --git a/lighthouse-core/audits/image-size-responsive.js b/lighthouse-core/audits/image-size-responsive.js
new file mode 100644
index 000000000..a0bfc79b4
--- /dev/null
+++ b/lighthouse-core/audits/image-size-responsive.js
@@ -0,0 +1,241 @@
+/**
+ * @license Copyright 2020 The Lighthouse Authors. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
+ */
+/**
+ * @fileoverview Checks to see if the size of the visible images used on
+ *   the page are large enough with respect to the pixel ratio. The
+ *   audit will list all visible images that are too small.
+ */
+'use strict';
+
+const Audit = require('./audit.js');
+const URL = require('../lib/url-shim.js');
+const i18n = require('../lib/i18n/i18n.js');
+
+const UIStrings = {
+  /** Title of a Lighthouse audit that provides detail on the size of visible images on the page. This descriptive title is shown to users when all images have correct sizes. */
+  title: 'Displays images with appropriate size',
+  /** Title of a Lighthouse audit that provides detail on the size of visible images on the page. This descriptive title is shown to users when not all images have correct sizes. */
+  failureTitle: 'Displays images with inappropriate size',
+  /** Description of a Lighthouse audit that tells the user why they should maintain an appropriate size for all images. This is displayed after a user expands the section to see more. No character length limits. 'Learn More' becomes link text to additional documentation. */
+  description: 'Image natural dimensions should be proportional to the display size and the ' +
+    'pixel ratio to maximize image clarity. [Learn more](https://web.dev/image-size-responsive).',
+  /**  Label for a column in a data table; entries in the column will be a string representing the displayed size of the image. */
+  columnDisplayed: 'Displayed size',
+  /**  Label for a column in a data table; entries in the column will be a string representing the actual size of the image. */
+  columnActual: 'Actual size',
+  /**  Label for a column in a data table; entries in the column will be a string representing the expected size of the image. */
+  columnExpected: 'Expected size',
+};
+
+const str_ = i18n.createMessageInstanceIdFn(__filename, UIStrings);
+
+// Factors used to allow for smaller effective density.
+// A factor of 1 means the actual device pixel density will be used.
+// A factor of 0.5, means half the density is required. For example if the device pixel ratio is 3,
+// then the images should have at least a density of 1.5.
+const SMALL_IMAGE_FACTOR = 1.0;
+const LARGE_IMAGE_FACTOR = 0.75;
+
+// An image has must have both its dimensions lower or equal to the threshold in order to be
+// considered SMALL.
+const SMALL_IMAGE_THRESHOLD = 64;
+
+/** @typedef {{url: string, elidedUrl: string, displayedSize: string, actualSize: string, actualPixels: number, expectedSize: string, expectedPixels: number}} Result */
+
+/**
+ * @param {{top: number, bottom: number, left: number, right: number}} imageRect
+ * @param {{innerWidth: number, innerHeight: number}} viewportDimensions
+ * @return {boolean}
+ */
+function isVisible(imageRect, viewportDimensions) {
+  return (
+    (imageRect.bottom - imageRect.top) * (imageRect.right - imageRect.left) > 0 &&
+    imageRect.top <= viewportDimensions.innerHeight &&
+    imageRect.bottom >= 0 &&
+    imageRect.left <= viewportDimensions.innerWidth &&
+    imageRect.right >= 0
+  );
+}
+
+/**
+ * @param {LH.Artifacts.ImageElement} image
+ * @return {boolean}
+ */
+function isCandidate(image) {
+  if (image.displayedWidth <= 1 || image.displayedHeight <= 1) {
+    return false;
+  }
+  if (image.naturalWidth === 0 || image.naturalHeight === 0) {
+    return false;
+  }
+  if (image.mimeType === 'image/svg+xml') {
+    return false;
+  }
+  if (image.isCss) {
+    return false;
+  }
+  if (image.usesObjectFit) {
+    return false;
+  }
+  if (image.usesPixelArtScaling) {
+    return false;
+  }
+  if (image.usesSrcSetDensityDescriptor) {
+    return false;
+  }
+  return true;
+}
+
+/**
+ * @param {LH.Artifacts.ImageElement} image
+ * @param {number} DPR
+ * @return {boolean}
+ */
+function imageHasRightSize(image, DPR) {
+  const [expectedWidth, expectedHeight] =
+      allowedImageSize(image.displayedWidth, image.displayedHeight, DPR);
+  return image.naturalWidth >= expectedWidth && image.naturalHeight >= expectedHeight;
+}
+
+/**
+ * @param {LH.Artifacts.ImageElement} image
+ * @param {number} DPR
+ * @return {Result}
+ */
+function getResult(image, DPR) {
+  const [expectedWidth, expectedHeight] =
+      expectedImageSize(image.displayedWidth, image.displayedHeight, DPR);
+  return {
+    url: image.src,
+    elidedUrl: URL.elideDataURI(image.src),
+    displayedSize: `${image.displayedWidth} x ${image.displayedHeight}`,
+    actualSize: `${image.naturalWidth} x ${image.naturalHeight}`,
+    actualPixels: image.naturalWidth * image.naturalHeight,
+    expectedSize: `${expectedWidth} x ${expectedHeight}`,
+    expectedPixels: expectedWidth * expectedHeight,
+  };
+}
+
+/**
+ * Compute the size an image should have given the display dimensions and pixel density in order to
+ * pass the audit.
+ *
+ * For smaller images, typically icons, the size must be proportional to the density.
+ * For larger images some tolerance is allowed as in those cases the perceived degradation is not
+ * that bad.
+ *
+ * @param {number} displayedWidth
+ * @param {number} displayedHeight
+ * @param {number} DPR
+ * @return {[number, number]}
+ */
+function allowedImageSize(displayedWidth, displayedHeight, DPR) {
+  let factor = SMALL_IMAGE_FACTOR;
+  if (displayedWidth > SMALL_IMAGE_THRESHOLD || displayedHeight > SMALL_IMAGE_THRESHOLD) {
+    factor = LARGE_IMAGE_FACTOR;
+  }
+  const width = Math.ceil(factor * DPR * displayedWidth);
+  const height = Math.ceil(factor * DPR * displayedHeight);
+  return [width, height];
+}
+
+/**
+ * Compute the size an image should have given the display dimensions and pixel density.
+ *
+ * @param {number} displayedWidth
+ * @param {number} displayedHeight
+ * @param {number} DPR
+ * @return {[number, number]}
+ */
+function expectedImageSize(displayedWidth, displayedHeight, DPR) {
+  const width = Math.ceil(DPR * displayedWidth);
+  const height = Math.ceil(DPR * displayedHeight);
+  return [width, height];
+}
+
+/**
+ * Remove repeated entries for the same source.
+ *
+ * It will keep the entry with the largest expected size.
+ *
+ * @param {Result[]} results
+ * @return {Result[]}
+ */
+function deduplicateResultsByUrl(results) {
+  results.sort((a, b) => a.url === b.url ? 0 : (a.url < b. url ? -1 : 1));
+  const deduplicated = /** @type {Result[]} */ ([]);
+  for (const r of results) {
+    const previousResult = deduplicated[deduplicated.length - 1];
+    if (previousResult && previousResult.url === r.url) {
+      // If the URL was the same, this is a duplicate. Keep the largest image.
+      if (previousResult.expectedPixels < r.expectedPixels) {
+        deduplicated[deduplicated.length - 1] = r;
+      }
+    } else {
+      deduplicated.push(r);
+    }
+  }
+  return deduplicated;
+}
+
+/**
+ * Sort entries in descending order by the magnitude of the size deficit, i.e. most pressing issues listed first.
+ *
+ * @param {Result[]} results
+ * @return {Result[]}
+ */
+function sortResultsBySizeDelta(results) {
+  return results.sort(
+      (a, b) => (b.expectedPixels - b.actualPixels) - (a.expectedPixels - a.actualPixels));
+}
+
+class ImageSizeResponsive extends Audit {
+  /**
+   * @return {LH.Audit.Meta}
+   */
+  static get meta() {
+    return {
+      id: 'image-size-responsive',
+      title: str_(UIStrings.title),
+      failureTitle: str_(UIStrings.failureTitle),
+      description: str_(UIStrings.description),
+      requiredArtifacts: ['ImageElements', 'ViewportDimensions'],
+    };
+  }
+
+  /**
+   * @param {LH.Artifacts} artifacts
+   * @return {LH.Audit.Product}
+   */
+  static audit(artifacts) {
+    const DPR = artifacts.ViewportDimensions.devicePixelRatio;
+    const results = Array
+      .from(artifacts.ImageElements)
+      .filter(isCandidate)
+      .filter(image => !imageHasRightSize(image, DPR))
+      .filter(image => isVisible(image.clientRect, artifacts.ViewportDimensions))
+      .map(image => getResult(image, DPR));
+
+    /** @type {LH.Audit.Details.Table['headings']} */
+    const headings = [
+      {key: 'url', itemType: 'thumbnail', text: ''},
+      {key: 'elidedUrl', itemType: 'url', text: str_(i18n.UIStrings.columnURL)},
+      {key: 'displayedSize', itemType: 'text', text: str_(UIStrings.columnDisplayed)},
+      {key: 'actualSize', itemType: 'text', text: str_(UIStrings.columnActual)},
+      {key: 'expectedSize', itemType: 'text', text: str_(UIStrings.columnExpected)},
+    ];
+
+    const finalResults = sortResultsBySizeDelta(deduplicateResultsByUrl(results));
+
+    return {
+      score: Number(results.length === 0),
+      details: Audit.makeTableDetails(headings, finalResults),
+    };
+  }
+}
+
+module.exports = ImageSizeResponsive;
+module.exports.UIStrings = UIStrings;
diff --git a/lighthouse-core/config/default-config.js b/lighthouse-core/config/default-config.js
index b2f3ce120..605ccf5ca 100644
--- a/lighthouse-core/config/default-config.js
+++ b/lighthouse-core/config/default-config.js
@@ -203,6 +203,7 @@ const defaultConfig = {
     'maskable-icon',
     'content-width',
     'image-aspect-ratio',
+    'image-size-responsive',
     'deprecations',
     'mainthread-work-breakdown',
     'bootup-time',
@@ -521,6 +522,7 @@ const defaultConfig = {
         {id: 'password-inputs-can-be-pasted-into', weight: 1},
         {id: 'errors-in-console', weight: 1},
         {id: 'image-aspect-ratio', weight: 1},
+        {id: 'image-size-responsive', weight: 1},
       ],
     },
     'seo': {
diff --git a/lighthouse-core/lib/i18n/locales/en-US.json b/lighthouse-core/lib/i18n/locales/en-US.json
index 6971d2883..285d84509 100644
--- a/lighthouse-core/lib/i18n/locales/en-US.json
+++ b/lighthouse-core/lib/i18n/locales/en-US.json
@@ -779,6 +779,24 @@
   "lighthouse-core/audits/image-aspect-ratio.js | warningCompute": {
     "message": "Invalid image sizing information {url}"
   },
+  "lighthouse-core/audits/image-size-responsive.js | columnActual": {
+    "message": "Actual size"
+  },
+  "lighthouse-core/audits/image-size-responsive.js | columnDisplayed": {
+    "message": "Displayed size"
+  },
+  "lighthouse-core/audits/image-size-responsive.js | columnExpected": {
+    "message": "Expected size"
+  },
+  "lighthouse-core/audits/image-size-responsive.js | description": {
+    "message": "Image natural dimensions should be proportional to the display size and the pixel ratio to maximize image clarity. [Learn more](https://web.dev/image-size-responsive)."
+  },
+  "lighthouse-core/audits/image-size-responsive.js | failureTitle": {
+    "message": "Displays images with inappropriate size"
+  },
+  "lighthouse-core/audits/image-size-responsive.js | title": {
+    "message": "Displays images with appropriate size"
+  },
   "lighthouse-core/audits/installable-manifest.js | description": {
     "message": "Browsers can proactively prompt users to add your app to their homescreen, which can lead to higher engagement. [Learn more](https://web.dev/installable-manifest)."
   },
diff --git a/lighthouse-core/lib/i18n/locales/en-XL.json b/lighthouse-core/lib/i18n/locales/en-XL.json
index 839a9c7c7..df8d2e728 100644
--- a/lighthouse-core/lib/i18n/locales/en-XL.json
+++ b/lighthouse-core/lib/i18n/locales/en-XL.json
@@ -779,6 +779,24 @@
   "lighthouse-core/audits/image-aspect-ratio.js | warningCompute": {
     "message": "Îńv̂ál̂íd̂ ím̂áĝé ŝíẑín̂ǵ îńf̂ór̂ḿât́îón̂ {url}"
   },
+  "lighthouse-core/audits/image-size-responsive.js | columnActual": {
+    "message": "Âćt̂úâĺ ŝíẑé"
+  },
+  "lighthouse-core/audits/image-size-responsive.js | columnDisplayed": {
+    "message": "D̂íŝṕl̂áŷéd̂ śîźê"
+  },
+  "lighthouse-core/audits/image-size-responsive.js | columnExpected": {
+    "message": "Êx́p̂éĉt́êd́ ŝíẑé"
+  },
+  "lighthouse-core/audits/image-size-responsive.js | description": {
+    "message": "Îḿâǵê ńât́ûŕâĺ d̂ím̂én̂śîón̂ś ŝh́ôúl̂d́ b̂é p̂ŕôṕôŕt̂íôńâĺ t̂ó t̂h́ê d́îśp̂ĺâý ŝíẑé âńd̂ t́ĥé p̂íx̂él̂ ŕât́îó t̂ó m̂áx̂ím̂íẑé îḿâǵê ćl̂ár̂ít̂ý. [L̂éâŕn̂ ḿôŕê](https://web.dev/image-size-responsive)."
+  },
+  "lighthouse-core/audits/image-size-responsive.js | failureTitle": {
+    "message": "D̂íŝṕl̂áŷś îḿâǵêś ŵít̂h́ îńâṕp̂ŕôṕr̂íât́ê śîźê"
+  },
+  "lighthouse-core/audits/image-size-responsive.js | title": {
+    "message": "D̂íŝṕl̂áŷś îḿâǵêś ŵít̂h́ âṕp̂ŕôṕr̂íât́ê śîźê"
+  },
   "lighthouse-core/audits/installable-manifest.js | description": {
     "message": "B̂ŕôẃŝér̂ś ĉán̂ ṕr̂óâćt̂ív̂él̂ý p̂ŕôḿp̂t́ ûśêŕŝ t́ô ád̂d́ ŷóûŕ âṕp̂ t́ô t́ĥéîŕ ĥóm̂éŝćr̂éêń, ŵh́îćĥ ćâń l̂éâd́ t̂ó ĥíĝh́êŕ êńĝáĝém̂én̂t́. [L̂éâŕn̂ ḿôŕê](https://web.dev/installable-manifest)."
   },
diff --git a/lighthouse-core/scripts/dogfood-lhci.sh b/lighthouse-core/scripts/dogfood-lhci.sh
index e72af7def..eb012f993 100755
--- a/lighthouse-core/scripts/dogfood-lhci.sh
+++ b/lighthouse-core/scripts/dogfood-lhci.sh
@@ -41,4 +41,8 @@ npm install -g @lhci/cli@0.3.x
 # Collect our LHCI results.
 lhci collect --staticDistDir=./dist/now/english/
 # Upload the results to our canary server.
-lhci upload --serverBaseUrl="$LHCI_CANARY_SERVER_URL" --token="$LHCI_CANARY_SERVER_TOKEN" --github-token="$BUNDLESIZE_GITHUB_TOKEN"
+lhci upload \
+  --serverBaseUrl="$LHCI_CANARY_SERVER_URL" \
+  --token="$LHCI_CANARY_SERVER_TOKEN" \
+  --github-token="$BUNDLESIZE_GITHUB_TOKEN" \
+  --ignoreDuplicateBuildFailure
diff --git a/package.json b/package.json
index f05bea6b0..3761ba7b7 100644
--- a/package.json
+++ b/package.json
@@ -198,7 +198,7 @@
     },
     {
       "path": "./dist/lighthouse-dt-bundle.js",
-      "maxSize": "455 kB"
+      "maxSize": "456 kB"
     },
     {
       "path": "./dist/lightrider/report-generator-bundle.js",
diff --git a/proto/sample_v2_round_trip.json b/proto/sample_v2_round_trip.json
index a63929fdf..a64b4fa3f 100644
--- a/proto/sample_v2_round_trip.json
+++ b/proto/sample_v2_round_trip.json
@@ -1123,6 +1123,53 @@
             "title": "Displays images with incorrect aspect ratio",
             "warnings": []
         },
+        "image-size-responsive": {
+            "description": "Image natural dimensions should be proportional to the display size and the pixel ratio to maximize image clarity. [Learn more](https://web.dev/image-size-responsive).",
+            "details": {
+                "headings": [
+                    {
+                        "itemType": "thumbnail",
+                        "key": "url"
+                    },
+                    {
+                        "itemType": "url",
+                        "key": "elidedUrl",
+                        "text": "URL"
+                    },
+                    {
+                        "itemType": "text",
+                        "key": "displayedSize",
+                        "text": "Displayed size"
+                    },
+                    {
+                        "itemType": "text",
+                        "key": "actualSize",
+                        "text": "Actual size"
+                    },
+                    {
+                        "itemType": "text",
+                        "key": "expectedSize",
+                        "text": "Expected size"
+                    }
+                ],
+                "items": [
+                    {
+                        "actualPixels": 152640.0,
+                        "actualSize": "480 x 318",
+                        "displayedSize": "480 x 318",
+                        "elidedUrl": "http://localhost:10200/dobetterweb/lighthouse-480x318.jpg",
+                        "expectedPixels": 1052100.0,
+                        "expectedSize": "1260 x 835",
+                        "url": "http://localhost:10200/dobetterweb/lighthouse-480x318.jpg"
+                    }
+                ],
+                "type": "table"
+            },
+            "id": "image-size-responsive",
+            "score": 0.0,
+            "scoreDisplayMode": "binary",
+            "title": "Displays images with inappropriate size"
+        },
         "input-image-alt": {
             "description": "When an image is being used as an `<input>` button, providing alternative text can help screen reader users understand the purpose of the button. [Learn more](https://web.dev/input-image-alt/).",
             "id": "input-image-alt",
@@ -3787,10 +3834,14 @@
                 {
                     "id": "image-aspect-ratio",
                     "weight": 1.0
+                },
+                {
+                    "id": "image-size-responsive",
+                    "weight": 1.0
                 }
             ],
             "id": "best-practices",
-            "score": 0.07,
+            "score": 0.06,
             "title": "Best Practices"
         },
         "performance": {
@@ -4725,6 +4776,12 @@
                 "name": "lh:audit:image-aspect-ratio",
                 "startTime": 0.0
             },
+            {
+                "duration": 100.0,
+                "entryType": "measure",
+                "name": "lh:audit:image-size-responsive",
+                "startTime": 0.0
+            },
             {
                 "duration": 100.0,
                 "entryType": "measure",
diff --git a/readme.md b/readme.md
index f9a7cb2a5..bb6672676 100644
--- a/readme.md
+++ b/readme.md
@@ -355,7 +355,7 @@ This section details services that have integrated Lighthouse data. If you're wo
 
 * **[Fluxguard](https://fluxguard.com/)** - Fluxguard provides website DOM change monitoring orchestrated with Google Puppeteer, and audited by Lighthouse. Fluxguard is a freemium product, with monthly monitoring of up to 75 pages for free.
 
-* **[PageSpeed Green](https://pagespeed.green/)** - New web performance monitoring service for web pages. For now, you can track PageSpeed performance indicators for unlimited domains and web pages. Powered By Google Lighthouse and Puppeteer. PageSpeed Green is a paid product with a free 30-day trial.
+* **[PageSpeed Green](https://pagespeed.green/)** - Web performance monitoring service for web sites. Track PageSpeed performance indicators for unlimited web pages from multiple regions. Check all code changes for PageSpeed degradations by integrating to your CD/CI using CLI. Powered By Google Lighthouse and Puppeteer. PageSpeed Green is a paid product with a free 14-day trial.
 
 * **[SpeedCurve](https://speedcurve.com)** — SpeedCurve is a tool for continuously monitoring web performance across different browsers, devices, and regions. It can aggregate any metric including Lighthouse scores across multiple pages and sites, and allows you to set performance budgets with Slack or email alerts. SpeedCurve is a paid product with a free 30-day trial.
 
diff --git a/third-party/snyk/snapshot.json b/third-party/snyk/snapshot.json
index 12c2c8b38..6198a8a1d 100644
--- a/third-party/snyk/snapshot.json
+++ b/third-party/snyk/snapshot.json
@@ -40,6 +40,7 @@
       {"id":"npm:bootstrap:20120510","severity":"medium","semver":{"vulnerable":["<2.1.0"]}}
     ],
     "dojo":[
+      {"id":"SNYK-JS-DOJO-559224","severity":"medium","semver":{"vulnerable":["<1.11.10",">=1.12.0 <1.12.8",">=1.13.0 <1.13.7",">=1.14.0 <1.14.6",">=1.15.0 <1.15.3",">=1.16.0 <1.16.2"]}},
       {"id":"SNYK-JS-DOJO-174934","severity":"medium","semver":{"vulnerable":[">=1.0.0 <1.0.3",">=1.1.0 <1.1.2",">=1.2.0 <1.2.4",">=1.3.0 <1.3.3",">=1.4.0 <1.4.2"]}},
       {"id":"SNYK-JS-DOJO-174933","severity":"medium","semver":{"vulnerable":["<1.2.0"]}},
       {"id":"SNYK-JS-DOJO-72305","severity":"medium","semver":{"vulnerable":["<1.14"]}},


Test patch:
diff --git a/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap b/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap
index ceb3757ed..96d9629e2 100644
--- a/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap
+++ b/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap
@@ -96,6 +96,9 @@ Object {
     Object {
       "path": "image-aspect-ratio",
     },
+    Object {
+      "path": "image-size-responsive",
+    },
     Object {
       "path": "deprecations",
     },
@@ -748,6 +751,10 @@ Object {
           "id": "image-aspect-ratio",
           "weight": 1,
         },
+        Object {
+          "id": "image-size-responsive",
+          "weight": 1,
+        },
       ],
       "title": "Best Practices",
     },
diff --git a/lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html b/lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html
index 727e6543c..403af919f 100644
--- a/lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html
+++ b/lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html
@@ -201,9 +201,18 @@
 </template>
 
 <!-- FAIL(image-aspect-ratio): image is naturally 480x318 -->
-<img src="lighthouse-480x318.jpg" width="480" height="57">
+<img src="lighthouse-480x318.jpg?iar1" width="120" height="15">
 <!-- PASS(image-aspect-ratio) -->
-<img src="lighthouse-480x318.jpg" width="480" height="318">
+<img src="lighthouse-480x318.jpg?iar2" width="120" height="80">
+
+<!-- FAIL(image-size-responsive): image is naturally 480x318 -->
+<img src="lighthouse-480x318.jpg?isr1" width="4800" height="3180" style="position: absolute;">
+<!-- PASS(image-size-responsive) -->
+<img src="lighthouse-480x318.jpg?isr2" width="120" height="80" style="position: absolute;">
+<!-- PASS(image-size-responsive) -->
+<img src="lighthouse-480x318.jpg?isr3" width="960" height="636" style="image-rendering: pixelated; position: absolute;">
+<!-- PASS(image-size-responsive) -->
+<img src="lighthouse-480x318.jpg?isr4" srcset="lighthouse-480x318.jpg 2x" width="960" height="636" style="position: absolute;">
 
 <!-- FAIL(efficient-animated-content): animated gif found -->
 <img src="lighthouse-rotating.gif" width="811" height="462">
diff --git a/lighthouse-cli/test/smokehouse/test-definitions/dobetterweb/dbw-expectations.js b/lighthouse-cli/test/smokehouse/test-definitions/dobetterweb/dbw-expectations.js
index 139faf8ea..8c1bd4d14 100644
--- a/lighthouse-cli/test/smokehouse/test-definitions/dobetterweb/dbw-expectations.js
+++ b/lighthouse-cli/test/smokehouse/test-definitions/dobetterweb/dbw-expectations.js
@@ -353,7 +353,19 @@ const expectations = [
           details: {
             items: {
               0: {
-                displayedAspectRatio: /^480 x 57/,
+                displayedAspectRatio: /^120 x 15/,
+                url: 'http://localhost:10200/dobetterweb/lighthouse-480x318.jpg?iar1',
+              },
+              length: 1,
+            },
+          },
+        },
+        'image-size-responsive': {
+          score: 0,
+          details: {
+            items: {
+              0: {
+                url: 'http://localhost:10200/dobetterweb/lighthouse-480x318.jpg?isr1',
               },
               length: 1,
             },
@@ -385,10 +397,10 @@ const expectations = [
         },
         'dom-size': {
           score: 1,
-          numericValue: 143,
+          numericValue: 147,
           details: {
             items: [
-              {statistic: 'Total DOM Elements', value: '143'},
+              {statistic: 'Total DOM Elements', value: '147'},
               {statistic: 'Maximum DOM Depth', value: '4'},
               {
                 statistic: 'Maximum Child Elements',
diff --git a/lighthouse-core/test/audits/image-size-responsive-test.js b/lighthouse-core/test/audits/image-size-responsive-test.js
new file mode 100644
index 000000000..cc61c27dc
--- /dev/null
+++ b/lighthouse-core/test/audits/image-size-responsive-test.js
@@ -0,0 +1,399 @@
+/**
+ * @license Copyright 2020 The Lighthouse Authors. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
+ */
+'use strict';
+
+const ImageSizeResponsiveAudit = require('../../audits/image-size-responsive.js');
+const assert = require('assert');
+
+/* eslint-env jest */
+
+const WIDTH = 800;
+const HEIGHT = 600;
+
+function generateImage(clientSize, naturalSize, props, src = 'https://google.com/logo.png') {
+  const image = {src, mimeType: 'image/png'};
+  const clientRect = {
+    clientRect: {
+      top: 0,
+      bottom: clientSize.displayedHeight,
+      left: 0,
+      right: clientSize.displayedWidth,
+    },
+  };
+  Object.assign(image, clientSize, naturalSize, clientRect, props);
+  return image;
+}
+
+describe('Images: size audit', () => {
+  function testImage(condition, data) {
+    const description = `identifies when an image ${condition}`;
+    it(description, () => {
+      const result = ImageSizeResponsiveAudit.audit({
+        ImageElements: [
+          generateImage(
+            {displayedWidth: data.clientSize[0], displayedHeight: data.clientSize[1]},
+            {naturalWidth: data.naturalSize[0], naturalHeight: data.naturalSize[1]},
+            data.props
+          ),
+        ],
+        ViewportDimensions: {
+          innerWidth: WIDTH,
+          innerHeight: HEIGHT,
+          devicePixelRatio: data.devicePixelRatio || 1,
+        },
+      });
+      let details = '';
+      if (result.score === 0) {
+        const {displayedSize: displayed, actualSize: actual, expectedSize: expected} =
+            result.details.items[0];
+        details = ` (displayed: ${displayed}, actual: ${actual}, expected: ${expected})`;
+      }
+      assert.strictEqual(result.score, data.score, `score does not match${details}`);
+    });
+  }
+
+  testImage('invalid image', {
+    score: 0,
+    clientSize: [100, 100],
+    naturalSize: [5, 5],
+  });
+
+  describe('is empty', () => {
+    testImage('is empty along width', {
+      score: 1,
+      clientSize: [100, 100],
+      naturalSize: [0, 5],
+    });
+
+    testImage('is empty along height', {
+      score: 1,
+      clientSize: [100, 100],
+      naturalSize: [5, 0],
+    });
+  });
+
+  describe('too small to bother testing', () => {
+    testImage('is too small along width', {
+      score: 1,
+      clientSize: [1, 100],
+      naturalSize: [5, 5],
+    });
+
+    testImage('is too small along height', {
+      score: 1,
+      clientSize: [100, 1],
+      naturalSize: [5, 5],
+    });
+  });
+
+  testImage('is an SVG image', {
+    score: 1,
+    clientSize: [100, 100],
+    naturalSize: [5, 5],
+    props: {
+      mimeType: 'image/svg+xml',
+    },
+  });
+
+  testImage('is a css image', {
+    score: 1,
+    clientSize: [100, 100],
+    naturalSize: [5, 5],
+    props: {
+      isCss: true,
+    },
+  });
+
+  testImage('uses object-fit', {
+    score: 1,
+    clientSize: [100, 100],
+    naturalSize: [5, 5],
+    props: {
+      usesObjectFit: true,
+    },
+  });
+
+  testImage('uses PixelArt scaling', {
+    score: 1,
+    clientSize: [100, 100],
+    naturalSize: [5, 5],
+    props: {
+      usesPixelArtScaling: true,
+    },
+  });
+
+  testImage('uses srcset density descriptor', {
+    score: 1,
+    clientSize: [100, 100],
+    naturalSize: [5, 5],
+    props: {
+      usesSrcSetDensityDescriptor: true,
+    },
+  });
+
+  describe('visibility', () => {
+    testImage('has no client area', {
+      score: 1,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: 0,
+          bottom: 0,
+          left: 0,
+          right: 0,
+        },
+      },
+    });
+
+    testImage('is above the visible area', {
+      score: 1,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: -1 - 100,
+          bottom: -1,
+          left: 0,
+          right: 100,
+        },
+      },
+    });
+
+    testImage('is almost above the visible area', {
+      score: 0,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: - 100,
+          bottom: 0,
+          left: 0,
+          right: 100,
+        },
+      },
+    });
+
+    testImage('is below the visible area', {
+      score: 1,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: HEIGHT + 1,
+          bottom: HEIGHT + 1 + 100,
+          left: 0,
+          right: 100,
+        },
+      },
+    });
+
+    testImage('is almost below the visible area', {
+      score: 0,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: HEIGHT,
+          bottom: HEIGHT + 100,
+          left: 0,
+          right: 100,
+        },
+      },
+    });
+
+    testImage('is to the left of the visible area', {
+      score: 1,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: 0,
+          bottom: 100,
+          left: -1 - 100,
+          right: -1,
+        },
+      },
+    });
+
+    testImage('is almost to the left of the visible area', {
+      score: 0,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: 0,
+          bottom: 100,
+          left: -100,
+          right: 0,
+        },
+      },
+    });
+
+    testImage('is to the right of the visible area', {
+      score: 1,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: 0,
+          bottom: 100,
+          left: WIDTH + 1,
+          right: WIDTH + 1 + 100,
+        },
+      },
+    });
+
+    testImage('is almost to the right of the visible area', {
+      score: 0,
+      clientSize: [100, 100],
+      naturalSize: [5, 5],
+      props: {
+        clientRect: {
+          top: 0,
+          bottom: 100,
+          left: WIDTH,
+          right: WIDTH + 100,
+        },
+      },
+    });
+  });
+
+  describe('check size', () => {
+    describe('DPR = 1', () => {
+      testImage('is an icon with right size', {
+        score: 1,
+        clientSize: [64, 64],
+        naturalSize: [64, 64],
+      });
+
+      testImage('is an icon with an invalid size', {
+        score: 0,
+        clientSize: [64, 64],
+        naturalSize: [63, 63],
+      });
+
+      testImage('has right size', {
+        score: 1,
+        clientSize: [65, 65],
+        naturalSize: [49, 49],
+      });
+
+      testImage('has an invalid size', {
+        score: 0,
+        clientSize: [65, 65],
+        naturalSize: [48, 48],
+      });
+    });
+
+    describe('DPR = 2', () => {
+      testImage('is an icon with right size', {
+        score: 1,
+        clientSize: [64, 64],
+        naturalSize: [128, 128],
+        devicePixelRatio: 2,
+      });
+
+      testImage('is an icon with an invalid size', {
+        score: 0,
+        clientSize: [64, 64],
+        naturalSize: [127, 127],
+        devicePixelRatio: 2,
+      });
+
+      testImage('has right size', {
+        score: 1,
+        clientSize: [65, 65],
+        naturalSize: [98, 98],
+        devicePixelRatio: 2,
+      });
+
+      testImage('has an invalid size', {
+        score: 0,
+        clientSize: [65, 65],
+        naturalSize: [97, 97],
+        devicePixelRatio: 2,
+      });
+    });
+  });
+
+  it('de-dupes images', () => {
+    const result = ImageSizeResponsiveAudit.audit({
+      ImageElements: [
+        generateImage(
+          {displayedWidth: 80, displayedHeight: 40},
+          {naturalWidth: 40, naturalHeight: 20}
+        ),
+        generateImage(
+          {displayedWidth: 160, displayedHeight: 80},
+          {naturalWidth: 40, naturalHeight: 20}
+        ),
+        generateImage(
+          {displayedWidth: 60, displayedHeight: 30},
+          {naturalWidth: 40, naturalHeight: 20}
+        ),
+      ],
+      ViewportDimensions: {
+        innerWidth: WIDTH,
+        innerHeight: HEIGHT,
+        devicePixelRatio: 1,
+      },
+    });
+    assert.equal(result.details.items.length, 1);
+    assert.equal(result.details.items[0].expectedSize, '160 x 80');
+  });
+
+  it('sorts images by size delta', () => {
+    const result = ImageSizeResponsiveAudit.audit({
+      ImageElements: [
+        generateImage(
+          {displayedWidth: 80, displayedHeight: 40},
+          {naturalWidth: 40, naturalHeight: 20},
+          {},
+          'image1.png'
+        ),
+        generateImage(
+          {displayedWidth: 120, displayedHeight: 60},
+          {naturalWidth: 40, naturalHeight: 20},
+          {},
+          'image2.png'
+        ),
+        generateImage(
+          {displayedWidth: 90, displayedHeight: 45},
+          {naturalWidth: 40, naturalHeight: 20},
+          {},
+          'image3.png'
+        ),
+      ],
+      ViewportDimensions: {
+        innerWidth: WIDTH,
+        innerHeight: HEIGHT,
+        devicePixelRatio: 1,
+      },
+    });
+    assert.equal(result.details.items.length, 3);
+    const srcs = result.details.items.map(item => item.url);
+    assert.deepEqual(srcs, ['image2.png', 'image3.png', 'image1.png']);
+  });
+
+  it('shows the right expected size', () => {
+    const result = ImageSizeResponsiveAudit.audit({
+      ImageElements: [
+        generateImage(
+          {displayedWidth: 80, displayedHeight: 40},
+          {naturalWidth: 40, naturalHeight: 20}
+        ),
+      ],
+      ViewportDimensions: {
+        innerWidth: WIDTH,
+        innerHeight: HEIGHT,
+        devicePixelRatio: 2.71,
+      },
+    });
+    assert.equal(result.details.items.length, 1);
+    assert.equal(result.details.items[0].expectedSize, '217 x 109');
+  });
+});
diff --git a/lighthouse-core/test/results/sample_v2.json b/lighthouse-core/test/results/sample_v2.json
index e2646f087..e202a0449 100644
--- a/lighthouse-core/test/results/sample_v2.json
+++ b/lighthouse-core/test/results/sample_v2.json
@@ -630,6 +630,54 @@
         ]
       }
     },
+    "image-size-responsive": {
+      "id": "image-size-responsive",
+      "title": "Displays images with inappropriate size",
+      "description": "Image natural dimensions should be proportional to the display size and the pixel ratio to maximize image clarity. [Learn more](https://web.dev/image-size-responsive).",
+      "score": 0,
+      "scoreDisplayMode": "binary",
+      "details": {
+        "type": "table",
+        "headings": [
+          {
+            "key": "url",
+            "itemType": "thumbnail",
+            "text": ""
+          },
+          {
+            "key": "elidedUrl",
+            "itemType": "url",
+            "text": "URL"
+          },
+          {
+            "key": "displayedSize",
+            "itemType": "text",
+            "text": "Displayed size"
+          },
+          {
+            "key": "actualSize",
+            "itemType": "text",
+            "text": "Actual size"
+          },
+          {
+            "key": "expectedSize",
+            "itemType": "text",
+            "text": "Expected size"
+          }
+        ],
+        "items": [
+          {
+            "url": "http://localhost:10200/dobetterweb/lighthouse-480x318.jpg",
+            "elidedUrl": "http://localhost:10200/dobetterweb/lighthouse-480x318.jpg",
+            "displayedSize": "480 x 318",
+            "actualSize": "480 x 318",
+            "actualPixels": 152640,
+            "expectedSize": "1260 x 835",
+            "expectedPixels": 1052100
+          }
+        ]
+      }
+    },
     "deprecations": {
       "id": "deprecations",
       "title": "Uses deprecated APIs",
@@ -4179,10 +4227,14 @@
         {
           "id": "image-aspect-ratio",
           "weight": 1
+        },
+        {
+          "id": "image-size-responsive",
+          "weight": 1
         }
       ],
       "id": "best-practices",
-      "score": 0.07
+      "score": 0.06
     },
     "seo": {
       "title": "SEO",
@@ -4810,6 +4862,12 @@
         "duration": 100,
         "entryType": "measure"
       },
+      {
+        "startTime": 0,
+        "name": "lh:audit:image-size-responsive",
+        "duration": 100,
+        "entryType": "measure"
+      },
       {
         "startTime": 0,
         "name": "lh:audit:deprecations",
@@ -5763,6 +5821,7 @@
       "lighthouse-core/lib/i18n/i18n.js | columnURL": [
         "audits[errors-in-console].details.headings[0].text",
         "audits[image-aspect-ratio].details.headings[1].text",
+        "audits[image-size-responsive].details.headings[1].text",
         "audits.deprecations.details.headings[1].text",
         "audits[bootup-time].details.headings[0].text",
         "audits[network-rtt].details.headings[0].text",
@@ -5884,6 +5943,21 @@
       "lighthouse-core/audits/image-aspect-ratio.js | columnActual": [
         "audits[image-aspect-ratio].details.headings[3].text"
       ],
+      "lighthouse-core/audits/image-size-responsive.js | failureTitle": [
+        "audits[image-size-responsive].title"
+      ],
+      "lighthouse-core/audits/image-size-responsive.js | description": [
+        "audits[image-size-responsive].description"
+      ],
+      "lighthouse-core/audits/image-size-responsive.js | columnDisplayed": [
+        "audits[image-size-responsive].details.headings[2].text"
+      ],
+      "lighthouse-core/audits/image-size-responsive.js | columnActual": [
+        "audits[image-size-responsive].details.headings[3].text"
+      ],
+      "lighthouse-core/audits/image-size-responsive.js | columnExpected": [
+        "audits[image-size-responsive].details.headings[4].text"
+      ],
       "lighthouse-core/audits/deprecations.js | failureTitle": [
         "audits.deprecations.title"
       ],