fix(cloudflare): default image transform quality to 85 (#2037)

* fix(cloudflare): default image transform quality to 85

The Images binding applies no quality default of its own and encodes
near-losslessly when quality is omitted, so renditions without an
explicit `q` came out several times larger than the original (a 2048px
WebP at ~900 KB instead of ~100 KB with q=85) — defeating the point of
the transform. Astro's image service only appends `q` when a quality is
explicitly configured, so this was the common path for every EmDash
media rendition.

parseTransformParams now falls back to DEFAULT_TRANSFORM_QUALITY (85,
matching Cloudflare's URL-based image-resizing default) and the
Cloudflare endpoint always sends an explicit quality to the binding.

* docs(changeset): note edge-cache purge for image quality fix

Previously-served oversized renditions stay cached under the immutable
header until they expire; flag the purge step for upgraders (emdashbot).

* refactor(images): exempt PNG from default transform quality

Addressing review from khoinguyenpham04: an explicit PNG quality switches
the Images binding to lossy PNG8, so applying the lossy default to PNG
would silently degrade a lossless format. parseTransformParams now leaves
quality undefined unless requested (keeping ImageTransformOptions.quality
optional, so the public type is unchanged), and a new resolveTransformQuality
helper applies DEFAULT_TRANSFORM_QUALITY only to lossy WebP/AVIF/JPEG while
letting an explicit ?q= win for every format including PNG.

Author: swissky

.changeset/cloudflare-image-quality-default.md

@@ -0,0 +1,8 @@
+---
+"@emdash-cms/cloudflare": patch
+"emdash": patch
+---
+
+Fixes oversized image renditions on Cloudflare: transforms without an explicit quality were encoded near-losslessly by the Images binding (a 2048px WebP came out ~900 KB instead of ~100 KB). Lossy transforms (WebP/AVIF/JPEG) now default to quality 85, matching Cloudflare's image-resizing default. PNG output keeps no explicit quality — an explicit PNG quality switches the binding to lossy PNG8, which is not a safe default for a lossless format. An explicit `?q=` in the request URL still wins for every format.
+
+Note: image responses are cached with `Cache-Control: immutable, max-age=31536000` keyed on the request URL, so previously-served oversized renditions stay cached at the edge/browser until they expire. To benefit immediately after upgrading, purge the Cloudflare cache for your `/_image*` URLs (or the whole site cache).

packages/cloudflare/src/image-endpoint.ts

@@ -20,6 +20,7 @@ import {
 	matchInternalMediaKey,
 	originalMediaHeaders,
 	parseTransformParams,
+	resolveTransformQuality,
 	type ImageTransformFormat,
 } from "emdash/media/image-endpoint";
 
@@ -86,8 +87,14 @@ export const GET: APIRoute = async (ctx) => {
 		const transform: ImageTransform = {};
 		if (width) transform.width = width;
 		if (height) transform.height = height;
+		// Lossy formats get an explicit quality: the Images binding has no
+		// default of its own and encodes near-losslessly without one, producing
+		// renditions several times the size of the original. PNG is exempt —
+		// an explicit PNG quality switches the binding to lossy PNG8, which is
+		// not a safe default for a lossless format. An explicit `?q=` always wins.
 		const output: ImageOutputOptions = { format: outputMime };
-		if (quality) output.quality = quality;
+		const effectiveQuality = resolveTransformQuality(format, quality);
+		if (effectiveQuality !== undefined) output.quality = effectiveQuality;
 
 		const result = await images.input(source.body).transform(transform).output(output);
 		const response = result.response();

packages/core/src/media/image-endpoint.ts

@@ -20,6 +20,17 @@ export const ALLOWED_TRANSFORM_FORMATS = ["webp", "avif", "jpeg", "png"] as cons
 /** Default output format -- broad support, strong compression. */
 export const DEFAULT_TRANSFORM_FORMAT: ImageTransformFormat = "webp";
 
+/**
+ * Default output quality for lossy formats (WebP/AVIF/JPEG) when the request
+ * doesn't specify one. Matches the default Cloudflare applies to URL-based
+ * image transformations. The Images *binding* applies no default of its own
+ * and encodes near-losslessly when quality is omitted (a 2048px WebP comes
+ * out ~900 KB instead of ~100 KB), so the endpoint sends an explicit quality
+ * for lossy output. PNG is exempt: an explicit PNG quality switches the
+ * binding to lossy PNG8, which is not a safe default for a lossless format.
+ */
+export const DEFAULT_TRANSFORM_QUALITY = 85;
+
 /** Upper bound for a requested dimension; caps the work a single request asks for. */
 export const MAX_TRANSFORM_DIMENSION = 4000;
 
@@ -31,6 +42,11 @@ export interface ImageTransformOptions {
 	width?: number;
 	height?: number;
 	format: ImageTransformFormat;
+	/**
+	 * Explicitly-requested quality (1-100), or `undefined` when the request
+	 * carried no `q`. Callers apply their own default per format (see
+	 * {@link DEFAULT_TRANSFORM_QUALITY}); lossless PNG deliberately gets none.
+	 */
 	quality?: number;
 }
 
@@ -117,10 +133,30 @@ export type ParsedTransformParams =
 	| { ok: true; options: ImageTransformOptions }
 	| { ok: false; message: string };
 
+/**
+ * Resolve the quality to send to the image binding for a transform. An
+ * explicitly-requested quality always wins. Otherwise lossy formats
+ * (WebP/AVIF/JPEG) get {@link DEFAULT_TRANSFORM_QUALITY} because the Images
+ * binding encodes near-losslessly when quality is omitted; lossless PNG gets
+ * `undefined` because an explicit PNG quality switches the binding to lossy
+ * PNG8, which is not a safe default for a lossless format.
+ */
+export function resolveTransformQuality(
+	format: ImageTransformFormat,
+	requested: number | undefined,
+): number | undefined {
+	if (requested !== undefined) return requested;
+	return format === "png" ? undefined : DEFAULT_TRANSFORM_QUALITY;
+}
+
 /**
  * Parse and validate `?w=&h=&f=&q=` query params. Width is required (it sizes
  * the rendition); dimensions are bounded so a request can't ask for an
- * unbounded or nonsensical transform.
+ * unbounded or nonsensical transform. Format falls back to
+ * {@link DEFAULT_TRANSFORM_FORMAT} when not requested. `q` is validated when
+ * present but otherwise left `undefined` so the caller can apply a per-format
+ * default (lossy formats get one, lossless PNG does not — see
+ * {@link DEFAULT_TRANSFORM_QUALITY}).
  */
 export function parseTransformParams(params: URLSearchParams): ParsedTransformParams {
 	const width = parseDimension(params.get("w"));
@@ -139,8 +175,8 @@ export function parseTransformParams(params: URLSearchParams): ParsedTransformPa
 		format = formatRaw;
 	}
 
-	const qualityRaw = params.get("q");
 	let quality: number | undefined;
+	const qualityRaw = params.get("q");
 	if (qualityRaw !== null) {
 		const q = Number(qualityRaw);
 		if (!Number.isInteger(q) || q < 1 || q > 100) {

packages/core/tests/unit/media/image-endpoint.test.ts

@@ -4,8 +4,10 @@ import {
 	matchInternalMediaKey,
 	isSafeTransformKey,
 	parseTransformParams,
+	resolveTransformQuality,
 	isTransformFormat,
 	originalMediaHeaders,
+	DEFAULT_TRANSFORM_QUALITY,
 	MAX_TRANSFORM_DIMENSION,
 } from "../../../src/media/image-endpoint.js";
 
@@ -94,9 +96,15 @@ describe("parseTransformParams", () => {
 		});
 	});
 
-	it("defaults format to webp and leaves height/quality undefined", () => {
+	it("defaults format to webp, leaves quality and height undefined when not requested", () => {
+		// Quality stays undefined when no `q` is requested: the Cloudflare
+		// endpoint applies DEFAULT_TRANSFORM_QUALITY for lossy formats itself,
+		// while lossless PNG must get none (explicit PNG quality → lossy PNG8).
 		const r = parse("w=800");
-		expect(r).toEqual({ ok: true, options: { width: 800, format: "webp" } });
+		expect(r).toEqual({
+			ok: true,
+			options: { width: 800, format: "webp", quality: undefined },
+		});
 	});
 
 	it("rejects out-of-range and non-integer dimensions", () => {
@@ -121,6 +129,23 @@ describe("parseTransformParams", () => {
 	});
 });
 
+describe("resolveTransformQuality", () => {
+	it("applies the default quality to lossy formats when none is requested", () => {
+		expect(resolveTransformQuality("webp", undefined)).toBe(DEFAULT_TRANSFORM_QUALITY);
+		expect(resolveTransformQuality("avif", undefined)).toBe(DEFAULT_TRANSFORM_QUALITY);
+		expect(resolveTransformQuality("jpeg", undefined)).toBe(DEFAULT_TRANSFORM_QUALITY);
+	});
+
+	it("sends no quality for lossless PNG when none is requested (avoids PNG8)", () => {
+		expect(resolveTransformQuality("png", undefined)).toBeUndefined();
+	});
+
+	it("honors an explicitly requested quality for every format, including PNG", () => {
+		expect(resolveTransformQuality("webp", 70)).toBe(70);
+		expect(resolveTransformQuality("png", 70)).toBe(70);
+	});
+});
+
 describe("originalMediaHeaders", () => {
 	it("renders safe raster types inline with a sandbox CSP", () => {
 		const h = originalMediaHeaders("image/png");