Use SVG blur technique for raw layout images (#37022)

This PR switches to using an SVG filter for blurring placeholder images, rather than a CSS filter. It's based on the technique described in @cramforce's [blog post](https://www.industrialempathy.com/posts/image-optimizations/#blurry-placeholder).

One change I made to @cramforce's version was to increase the stdDeviation property of the SVG (which controls the gaussian blur strength) from .5 to 50. Smaller values than this tended to look bad, as our technique for generating the blurry placeholder image tends to produce images with sharp contrast between the pixels, which looks bad when blown up unless it's blurred by a substantial amount.

This PR currently only affects the experimental `layout="raw"` but I expect to eventually apply it to all images. CC: @styfle @kara

packages/next/client/image.tsx

@@ -704,15 +704,21 @@ export default function Image({
       }
     }
   }
-
   const imgStyle = Object.assign({}, style, layout === 'raw' ? {} : layoutStyle)
+  const svgBlurPlaceholder = `url("data:image/svg+xml;charset=utf-8,%3Csvg xmlns='http%3A//www.w3.org/2000/svg' xmlns%3Axlink='http%3A//www.w3.org/1999/xlink' viewBox='0 0 ${widthInt} ${heightInt}'%3E%3Cfilter id='b' color-interpolation-filters='sRGB'%3E%3CfeGaussianBlur stdDeviation='50'%3E%3C/feGaussianBlur%3E%3CfeComponentTransfer%3E%3CfeFuncA type='discrete' tableValues='1 1'%3E%3C/feFuncA%3E%3C/feComponentTransfer%3E%3C/filter%3E%3Cimage filter='url(%23b)' x='0' y='0' height='100%25' width='100%25' href='${blurDataURL}'%3E%3C/image%3E%3C/svg%3E");`
   const blurStyle =
     placeholder === 'blur' && !blurComplete
       ? {
-          filter: 'blur(20px)',
           backgroundSize: objectFit || 'cover',
-          backgroundImage: `url("${blurDataURL}")`,
           backgroundPosition: objectPosition || '0% 0%',
+          ...(layout === 'raw' && blurDataURL?.startsWith('data:image')
+            ? {
+                backgroundImage: svgBlurPlaceholder,
+              }
+            : {
+                filter: 'blur(20px)',
+                backgroundImage: `url("${blurDataURL}")`,
+              }),
         }
       : {}
   if (layout === 'fill') {

test/integration/image-component/base-path/test/static.test.js

@@ -70,20 +70,20 @@ const runTests = (isDev = false) => {
   })
   it('Should add a blur placeholder to statically imported jpg', async () => {
     expect(html).toContain(
-      `style="position:absolute;top:0;left:0;bottom:0;right:0;box-sizing:border-box;padding:0;border:none;margin:auto;display:block;width:0;height:0;min-width:100%;max-width:100%;min-height:100%;max-height:100%;filter:blur(20px);background-size:cover;background-image:url(${
+      `style="position:absolute;top:0;left:0;bottom:0;right:0;box-sizing:border-box;padding:0;border:none;margin:auto;display:block;width:0;height:0;min-width:100%;max-width:100%;min-height:100%;max-height:100%;background-size:cover;background-position:0% 0%;filter:blur(20px);background-image:url(${
         isDev
           ? '"/docs/_next/image?url=%2Fdocs%2F_next%2Fstatic%2Fmedia%2Ftest.fab2915d.jpg&w=8&q=70"'
           : '"data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wCEAAoKCgoKCgsMDAsPEA4QDxYUExMUFiIYGhgaGCIzICUgICUgMy03LCksNy1RQDg4QFFeT0pPXnFlZXGPiI+7u/sBCgoKCgoKCwwMCw8QDhAPFhQTExQWIhgaGBoYIjMgJSAgJSAzLTcsKSw3LVFAODhAUV5PSk9ecWVlcY+Ij7u7+//CABEIAAYACAMBIgACEQEDEQH/xAAnAAEBAAAAAAAAAAAAAAAAAAAABwEBAAAAAAAAAAAAAAAAAAAAAP/aAAwDAQACEAMQAAAAmgP/xAAcEAACAQUBAAAAAAAAAAAAAAASFBMAAQMFERX/2gAIAQEAAT8AZ1HjrKZX55JysIc4Ff/EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAIAQIBAT8Af//EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAIAQMBAT8Af//Z"'
-      });background-position:0% 0%"`
+      })`
     )
   })
   it('Should add a blur placeholder to statically imported png', async () => {
     expect(html).toContain(
-      `style="position:absolute;top:0;left:0;bottom:0;right:0;box-sizing:border-box;padding:0;border:none;margin:auto;display:block;width:0;height:0;min-width:100%;max-width:100%;min-height:100%;max-height:100%;filter:blur(20px);background-size:cover;background-image:url(${
+      `style="position:absolute;top:0;left:0;bottom:0;right:0;box-sizing:border-box;padding:0;border:none;margin:auto;display:block;width:0;height:0;min-width:100%;max-width:100%;min-height:100%;max-height:100%;background-size:cover;background-position:0% 0%;filter:blur(20px);background-image:url(${
         isDev
           ? '"/docs/_next/image?url=%2Fdocs%2F_next%2Fstatic%2Fmedia%2Ftest.3f1a293b.png&w=8&q=70"'
           : '"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAMAAAAICAAAAAAZhBqgAAAAJklEQVR42mNgkmBkYGXgZGBoY2Co/lPAcOf/dYaCzHwGEBAVEwUAZZIG0TbWicQAAAAASUVORK5CYII="'
-      });background-position:0% 0%"`
+      })`
     )
   })
 }

test/integration/image-component/default/pages/static-img.js

@@ -23,6 +23,12 @@ const Page = () => {
         layout="fixed"
         placeholder="blur"
       />
+      <Image
+        id="basic-static-raw"
+        src={testImg}
+        layout="raw"
+        placeholder="blur"
+      />
       <TallImage />
       <Image
         id="defined-size-static"

test/integration/image-component/default/test/index.test.js

@@ -788,7 +788,7 @@ function runTests(mode) {
     )
     expect(await browser.elementById('raw1').getAttribute('sizes')).toBeNull()
     expect(await browser.elementById('raw1').getAttribute('style')).toMatch(
-      'filter:blur(20px);background-size:cover;'
+      'background-size:cover;background-position:0% 0%;'
     )
     expect(await browser.elementById('raw1').getAttribute('height')).toBe('400')
     expect(await browser.elementById('raw1').getAttribute('width')).toBe('400')
@@ -825,7 +825,7 @@ function runTests(mode) {
       'lazy'
     )
     expect(await browser.elementById('raw2').getAttribute('style')).toMatch(
-      'filter:blur(20px);background-size:cover;'
+      'background-size:cover;background-position:0% 0%;'
     )
     expect(await browser.elementById('raw2').getAttribute('height')).toBe('400')
     expect(await browser.elementById('raw2').getAttribute('width')).toBe('400')
@@ -1322,7 +1322,7 @@ function runTests(mode) {
     )
 
     expect($html('#blurry-placeholder-raw')[0].attribs.style).toContain(
-      `background-image:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='400' height='400' viewBox='0 0 400 400'%3E%3Cfilter id='blur' filterUnits='userSpaceOnUse' color-interpolation-filters='sRGB'%3E%3CfeGaussianBlur stdDeviation='20' edgeMode='duplicate' /%3E%3CfeComponentTransfer%3E%3CfeFuncA type='discrete' tableValues='1 1' /%3E%3C/feComponentTransfer%3E%3C/filter%3E%3Cimage filter='url(%23blur)' href='data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAMDAwMDAwQEBAQFBQUFBQcHBgYHBwsICQgJCAsRCwwLCwwLEQ8SDw4PEg8bFRMTFRsfGhkaHyYiIiYwLTA+PlT/wAALCAAKAAoBAREA/8QAMwABAQEAAAAAAAAAAAAAAAAAAAcJEAABAwUAAwAAAAAAAAAAAAAFAAYRAQMEEyEVMlH/2gAIAQEAAD8Az1bLPaxhiuk0QdeCOLDtHixN2dmd2bsc5FPX7VTREX//2Q==' x='0' y='0' height='100%25' width='100%25'/%3E%3C/svg%3E")`
+      `background-size:cover;background-position:0% 0%;background-image:url("data:image/svg+xml;charset=utf-8,%3Csvg xmlns='http%3A//www.w3.org/2000/svg' xmlns%3Axlink='http%3A//www.w3.org/1999/xlink' viewBox='0 0 400 400'%3E%3Cfilter id='b' color-interpolation-filters='sRGB'%3E%3CfeGaussianBlur stdDeviation='50'%3E%3C/feGaussianBlur%3E%3CfeComponentTransfer%3E%3CfeFuncA type='discrete' tableValues='1 1'%3E%3C/feFuncA%3E%3C/feComponentTransfer%3E%3C/filter%3E%3Cimage filter='url(%23b)' x='0' y='0' height='100%25' width='100%25' href='data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='400' height='400' viewBox='0 0 400 400'%3E%3Cfilter id='blur' filterUnits='userSpaceOnUse' color-interpolation-filters='sRGB'%3E%3CfeGaussianBlur stdDeviation='20' edgeMode='duplicate' /%3E%3CfeComponentTransfer%3E%3CfeFuncA type='discrete' tableValues='1 1' /%3E%3C/feComponentTransfer%3E%3C/filter%3E%3Cimage filter='url(%23blur)' href='data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAMDAwMDAwQEBAQFBQUFBQcHBgYHBwsICQgJCAsRCwwLCwwLEQ8SDw4PEg8bFRMTFRsfGhkaHyYiIiYwLTA+PlT/wAALCAAKAAoBAREA/8QAMwABAQEAAAAAAAAAAAAAAAAAAAcJEAABAwUAAwAAAAAAAAAAAAAFAAYRAQMEEyEVMlH/2gAIAQEAAD8Az1bLPaxhiuk0QdeCOLDtHixN2dmd2bsc5FPX7VTREX//2Q==' x='0' y='0' height='100%25' width='100%25'/%3E%3C/svg%3E'%3E%3C/image%3E%3C/svg%3E")`
     )
 
     expect($html('#blurry-placeholder')[0].attribs.style).toContain(

test/integration/image-component/default/test/static.test.js

@@ -66,12 +66,17 @@ const runTests = () => {
   })
   it('Should add a blur placeholder to statically imported jpg', async () => {
     expect(html).toContain(
-      `style="position:absolute;top:0;left:0;bottom:0;right:0;box-sizing:border-box;padding:0;border:none;margin:auto;display:block;width:0;height:0;min-width:100%;max-width:100%;min-height:100%;max-height:100%;filter:blur(20px);background-size:cover;background-image:url("data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wCEAAoKCgoKCgsMDAsPEA4QDxYUExMUFiIYGhgaGCIzICUgICUgMy03LCksNy1RQDg4QFFeT0pPXnFlZXGPiI+7u/sBCgoKCgoKCwwMCw8QDhAPFhQTExQWIhgaGBoYIjMgJSAgJSAzLTcsKSw3LVFAODhAUV5PSk9ecWVlcY+Ij7u7+//CABEIAAYACAMBIgACEQEDEQH/xAAnAAEBAAAAAAAAAAAAAAAAAAAABwEBAAAAAAAAAAAAAAAAAAAAAP/aAAwDAQACEAMQAAAAmgP/xAAcEAACAQUBAAAAAAAAAAAAAAASFBMAAQMFERX/2gAIAQEAAT8AZ1HjrKZX55JysIc4Ff/EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAIAQIBAT8Af//EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAIAQMBAT8Af//Z");background-position:0% 0%"`
+      `style="position:absolute;top:0;left:0;bottom:0;right:0;box-sizing:border-box;padding:0;border:none;margin:auto;display:block;width:0;height:0;min-width:100%;max-width:100%;min-height:100%;max-height:100%;background-size:cover;background-position:0% 0%;filter:blur(20px);background-image:url("data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wCEAAoKCgoKCgsMDAsPEA4QDxYUExMUFiIYGhgaGCIzICUgICUgMy03LCksNy1RQDg4QFFeT0pPXnFlZXGPiI+7u/sBCgoKCgoKCwwMCw8QDhAPFhQTExQWIhgaGBoYIjMgJSAgJSAzLTcsKSw3LVFAODhAUV5PSk9ecWVlcY+Ij7u7+//CABEIAAYACAMBIgACEQEDEQH/xAAnAAEBAAAAAAAAAAAAAAAAAAAABwEBAAAAAAAAAAAAAAAAAAAAAP/aAAwDAQACEAMQAAAAmgP/xAAcEAACAQUBAAAAAAAAAAAAAAASFBMAAQMFERX/2gAIAQEAAT8AZ1HjrKZX55JysIc4Ff/EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAIAQIBAT8Af//EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAIAQMBAT8Af//Z")"`
+    )
+  })
+  it('Should add a blur to a statically imported image in "raw" mode', async () => {
+    expect(html).toContain(
+      `style="background-size:cover;background-position:0% 0%;background-image:url("data:image/svg+xml;charset=utf-8,%3Csvg xmlns='http%3A//www.w3.org/2000/svg' xmlns%3Axlink='http%3A//www.w3.org/1999/xlink' viewBox='0 0 400 300'%3E%3Cfilter id='b' color-interpolation-filters='sRGB'%3E%3CfeGaussianBlur stdDeviation='50'%3E%3C/feGaussianBlur%3E%3CfeComponentTransfer%3E%3CfeFuncA type='discrete' tableValues='1 1'%3E%3C/feFuncA%3E%3C/feComponentTransfer%3E%3C/filter%3E%3Cimage filter='url(%23b)' x='0' y='0' height='100%25' width='100%25' href='data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wCEAAoKCgoKCgsMDAsPEA4QDxYUExMUFiIYGhgaGCIzICUgICUgMy03LCksNy1RQDg4QFFeT0pPXnFlZXGPiI+7u/sBCgoKCgoKCwwMCw8QDhAPFhQTExQWIhgaGBoYIjMgJSAgJSAzLTcsKSw3LVFAODhAUV5PSk9ecWVlcY+Ij7u7+//CABEIAAYACAMBIgACEQEDEQH/xAAnAAEBAAAAAAAAAAAAAAAAAAAABwEBAAAAAAAAAAAAAAAAAAAAAP/aAAwDAQACEAMQAAAAmgP/xAAcEAACAQUBAAAAAAAAAAAAAAASFBMAAQMFERX/2gAIAQEAAT8AZ1HjrKZX55JysIc4Ff/EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAIAQIBAT8Af//EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAIAQMBAT8Af//Z'%3E%3C/image%3E%3C/svg%3E");`
     )
   })
   it('Should add a blur placeholder to statically imported png', async () => {
     expect(html).toContain(
-      `style="position:absolute;top:0;left:0;bottom:0;right:0;box-sizing:border-box;padding:0;border:none;margin:auto;display:block;width:0;height:0;min-width:100%;max-width:100%;min-height:100%;max-height:100%;filter:blur(20px);background-size:cover;background-image:url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAgAAAAICAAAAADhZOFXAAAAOklEQVR42iWGsQkAIBDE0iuIdiLOJjiGIzjiL/Meb4okiNYIlLjK3hJMzCQG1/0qmXXOUkjAV+m9wAMe3QiV6Ne8VgAAAABJRU5ErkJggg==");background-position:0% 0%"`
+      `style="position:absolute;top:0;left:0;bottom:0;right:0;box-sizing:border-box;padding:0;border:none;margin:auto;display:block;width:0;height:0;min-width:100%;max-width:100%;min-height:100%;max-height:100%;background-size:cover;background-position:0% 0%;filter:blur(20px);background-image:url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAgAAAAICAAAAADhZOFXAAAAOklEQVR42iWGsQkAIBDE0iuIdiLOJjiGIzjiL/Meb4okiNYIlLjK3hJMzCQG1/0qmXXOUkjAV+m9wAMe3QiV6Ne8VgAAAABJRU5ErkJggg==")`
     )
   })
 }