PNG: default compression level 4

encode(), encodePNG(), encodeAPNG() and apngEncoder() default to zlib
level 4 instead of 1. Measured (our encoder, CPU time): graphic
891 -> 795 kB, readme screenshot 191 -> 149 kB, 1080p photo
2183 -> 1973 kB, external 560 -> 523 kB, for about +30% time
(photo 149 -> 196 ms). Level 3 compresses worse than 4 at no less time
(deflate_fast vs lazy matching), 6 nearly triples the photo's time.

sharp's default (level 6, no filter) stays ~10% smaller on the bench
graphic (it writes RGBA, which happens to compress better there), but
we're 29% smaller on photos at about its speed. Writing opaque images as
RGBA when smaller was measured and left out: it mostly helps small
synthetic images, costs ~8% always and makes decoding slower.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BsU2GAqbnFSNaYDBGD1Km2

Author: matmen

CHANGELOG.md

@@ -1,6 +1,12 @@
 # Changelog
 
-## 3.12.3
+## 3.13.0
+
+### Changes
+
+- PNG and APNG encoding (`encode()`, `encodePNG()`, `encodeAPNG()`, `apngEncoder()`) default to compression level 4
+  instead of 1: 7-22% smaller files (graphics 11%, photos 10%, screenshots 22%) for about 30% more time. zlib's lazy
+  matching starts at level 4, so levels 2-3 save less. Pass `compression: 1` for the previous speed.
 
 ### Performance
 

src/animation-encoder.ts

@@ -44,7 +44,7 @@ export interface GIFAnimationEncoderOptions extends AnimationEncoderOptions {
 
 /** Options of {@link Animation.apngEncoder} */
 export interface APNGAnimationEncoderOptions extends AnimationEncoderOptions {
-    /** The zlib compression level (0-9), higher is smaller but slower. Default: `1` */
+    /** The zlib compression level (0-9), higher is smaller but slower. Default: `4` */
     compression?: number;
 }
 
@@ -177,7 +177,7 @@ export class AnimationEncoder {
     }
 
     /** @internal */
-    static __apng__(width: number, height: number, { loopCount = -1, metadata = {}, optimize = true, compression = 1 }: APNGAnimationEncoderOptions): AnimationEncoder {
+    static __apng__(width: number, height: number, { loopCount = -1, metadata = {}, optimize = true, compression = 4 }: APNGAnimationEncoderOptions): AnimationEncoder {
         canvas(width, height, loopCount);
         const text = pngText(resolveMetadata(metadata));
         // the frames are kept compressed (quickly): the pixel format, and whether opaque animations are stored without

src/animation.ts

@@ -86,7 +86,7 @@ export interface GIFEncodeOptions extends AnimationEncodeOptions {
 
 /** Options of {@link Animation.encodeAPNG} */
 export interface APNGEncodeOptions extends AnimationEncodeOptions {
-    /** The zlib compression level (0-9), higher is smaller but slower. Default: `1` */
+    /** The zlib compression level (0-9), higher is smaller but slower. Default: `4` */
     compression?: number;
 }
 
@@ -279,11 +279,11 @@ export class Animation extends Array<Frame> {
      * the first frame. Each frame is stored as the area that changed since the frame before, identical frames are
      * merged (unless the `optimize` option is false): the file shows exactly the same animation, but doesn't
      * necessarily decode to the same frames
-     * @param compression The zlib compression level (0-9), higher is smaller but slower
+     * @param compression The zlib compression level (0-9), higher is smaller but slower. Default: `4`
      */
     encodeAPNG(compression?: number): Promise<Uint8Array>;
-    async encodeAPNG(compressionOrOptions: number | APNGEncodeOptions = 1): Promise<Uint8Array> {
-        const { compression = 1, metadata = {}, optimize = true } = isOptions(compressionOrOptions) ? compressionOrOptions : { compression: compressionOrOptions };
+    async encodeAPNG(compressionOrOptions: number | APNGEncodeOptions = 4): Promise<Uint8Array> {
+        const { compression = 4, metadata = {}, optimize = true } = isOptions(compressionOrOptions) ? compressionOrOptions : { compression: compressionOrOptions };
         this.__validate__();
         if (!this.length) throw new Error('An animation needs at least one frame');
 

src/image.ts

@@ -97,7 +97,7 @@ export interface SharpenOptions {
 
 /** Options of {@link Image.encode} */
 export interface PNGEncodeOptions {
-    /** The compression level (0-9). Default: `1` */
+    /** The compression level (0-9), higher is smaller but slower. Default: `4` */
     compression?: number;
     /** Metadata to include, see {@link Metadata} */
     metadata?: Metadata;
@@ -2115,23 +2115,23 @@ export class Image {
     encode(options?: PNGEncodeOptions): Promise<Uint8Array>;
     /**
      * Encodes the image into a PNG
-     * @param compression The compression level (0-9). Default: `1`
+     * @param compression The compression level (0-9). Default: `4`
      * @param metadata Metadata to include, see {@link Metadata}
      * @return The encoded data
      */
     encode(compression?: number, metadata?: Metadata): Promise<Uint8Array>;
     /**
-     * Encodes the image into a PNG with compression level 1
+     * Encodes the image into a PNG with compression level 4
      * @param metadata Metadata to include, see {@link Metadata}
      * @return The encoded data
      */
     encode(metadata?: Metadata): Promise<Uint8Array>;
-    async encode(compressionOrOptions: number | PNGEncodeOptions | Metadata = 1, metadataArgument: Metadata = {}): Promise<Uint8Array> {
-        let compression = 1, metadata = metadataArgument;
+    async encode(compressionOrOptions: number | PNGEncodeOptions | Metadata = 4, metadataArgument: Metadata = {}): Promise<Uint8Array> {
+        let compression = 4, metadata = metadataArgument;
         if (!isOptions(compressionOrOptions)) compression = compressionOrOptions;
         // the options and the metadata have no key in common: an object with neither is empty, the same either way
         else if ('compression' in compressionOrOptions || 'metadata' in compressionOrOptions)
-            ({ compression = 1, metadata = {} } = compressionOrOptions);
+            ({ compression = 4, metadata = {} } = compressionOrOptions);
         else metadata = compressionOrOptions as Metadata;
 
         const level = Math.min(9, Math.max(0, ~~finite(compression, 'compression level')));
@@ -2144,7 +2144,7 @@ export class Image {
     encodePNG(options?: PNGEncodeOptions): Promise<Uint8Array>;
     /**
      * Encodes the image into a PNG, an alias of {@link Image.encode}
-     * @param compression The compression level (0-9). Default: `1`
+     * @param compression The compression level (0-9). Default: `4`
      * @param metadata Metadata to include, see {@link Metadata}
      */
     encodePNG(compression?: number, metadata?: Metadata): Promise<Uint8Array>;