Zoom param support

README.md

@@ -53,6 +53,7 @@ It's really that simple!
 |`crop_strategy`|String, "smart", "entropy", "attention"|There are 3 automatic cropping strategies for use with `resize`: <ul><li>`attention`: good results, ~70% slower</li><li>`entropy`: mediocre results, ~30% slower</li><li>`smart`: best results, ~50% slower</li>|
 |`fit`|String, "w,h"|A comma separated string of the target maximum width and height. Does not crop the image.|
 |`crop`|Boolean\|String, "x,y,w,h"|Crop an image by percentages x-offset, y-offset, width and height (x,y,w,h). Percentages are used so that you don’t need to recalculate the cropping when transforming the image in other ways such as resizing it. You can crop by pixel values too by appending `px` to the values. `crop=160px,160px,788px,788px` takes a 788 by 788 pixel square starting at 160 by 160.|
+|`zoom`|Number|Zooms the image by the specified amount for high DPI displays. `zoom=2` produces an image twice the size specified in `w`, `h`, `fit` or `resize`. The quality is automatically reduced to keep file sizes roughly equivalent to the non-zoomed image unless the `quality` argument is passed.|
 |`webp`|Boolean, 1|Force WebP format.|
 |`lb`|String, "w,h"|Add letterboxing effect to images, by scaling them to width, height while maintaining the aspect ratio and filling the rest with black or `background`.|
 |`background`|String|Add background color via name (red) or hex value (%23ff0000). Don't forget to escape # as `%23`.|

index.js

@@ -39,10 +39,11 @@ module.exports.s3 = function(config, key, args, callback) {
 	);
 };
 
-var getDimArray = function( dims ) {
+var getDimArray = function( dims, zoom ) {
 	var dimArr = typeof dims === 'string' ? dims.split(',') : dims;
+	zoom = zoom || 1;
 	return dimArr.map(function(v) {
-		return Number(v) || null;
+		return (Number(v) * zoom) || null;
 	});
 }
 
@@ -104,9 +105,12 @@ module.exports.resizeBuffer = function(buffer, args, callback) {
 						});
 					}
 
+					// get zoom value
+					var zoom = parseFloat( args.zoom ) || 1;
+
 					// resize
 					if (args.resize) {
-						args.resize = getDimArray( args.resize );
+						args.resize = getDimArray( args.resize, zoom );
 
 						// apply cropping strategies
 						if ( args.gravity ) {
@@ -133,14 +137,14 @@ module.exports.resizeBuffer = function(buffer, args, callback) {
 							args.resize
 						);
 					} else if (args.fit) {
-						args.fit = getDimArray( args.fit );
+						args.fit = getDimArray( args.fit, zoom );
 						image.resize.apply(
 							image,
 							args.fit
 						);
 						image.max();
 					} else if (args.lb) {
-						args.lb = getDimArray( args.lb );
+						args.lb = getDimArray( args.lb, zoom );
 						image.resize.apply(
 							image,
 							args.lb
@@ -155,27 +159,36 @@ module.exports.resizeBuffer = function(buffer, args, callback) {
 						image.embed();
 					} else if (args.w || args.h) {
 						image.resize(
-							Number(args.w) || null,
-							Number(args.h) || null
+							(Number(args.w) * zoom) || null,
+							(Number(args.h) * zoom) || null
 						);
 						if (!args.crop) {
 							image.max();
 						}
 					}
 
+					// return a default compression value based on a logarithmic scale
+					// defaultValue = 100, zoom = 2; = 65
+					// defaultValue = 80, zoom = 2; = 50
+					// defaultValue = 100, zoom = 1.5; = 86
+					// defaultValue = 80, zoom = 1.5; = 68
+					var applyZoomCompression = function( defaultValue, zoom ) {
+						return Math.min(Math.max(Math.round( defaultValue - ( (Math.log(zoom) / Math.log(defaultValue / zoom)) * (defaultValue * zoom) ) ), Math.round(defaultValue / zoom)), defaultValue);
+					}
+
+					// set default quality slightly higher than sharp's default
+					if ( ! args.quality ) {
+						args.quality = applyZoomCompression( 82, zoom );
+					}
+
 					// allow override of compression quality
 					if (args.webp) {
 						image.webp({
-							quality: args.quality
-								? Math.min(Math.max(Number(args.quality), 0), 100)
-								: 80,
+							quality: Math.round(Math.min(Math.max(Number(args.quality), 0), 100)),
 						});
-					} else if (metadata.format === 'jpeg' && args.quality) {
+					} else if (metadata.format === 'jpeg') {
 						image.jpeg({
-							quality: Math.min(
-								Math.max(Number(args.quality), 0),
-								100
-							),
+							quality: Math.round(Math.min(Math.max(Number(args.quality), 0), 100)),
 						});
 					}