Use github.com/bamiaux/rez instead of github.com/nfnt/resize for resampling the pyramid tiles. It is much faster but needs some testing.

cmd/mtseeder/pyramid.go

@@ -18,7 +18,7 @@ import (
 
 	"bitbucket.org/s_l_teichmann/mtsatellite/common"
 
-	"github.com/nfnt/resize"
+	"github.com/bamiaux/rez"
 )
 
 func findMaxDir(files []os.FileInfo) (min, max int) {
@@ -155,7 +155,7 @@ var dps = [4]image.Point{
 	image.Pt(256, 256),
 	image.Pt(256, 0)}
 
-func fuseTile(scratch *image.RGBA, job *pyramidJob) error {
+func fuseTile(scratch, resized *image.RGBA, conv rez.Converter, job *pyramidJob) error {
 
 	for i, path := range job.src {
 
@@ -167,7 +167,9 @@ func fuseTile(scratch *image.RGBA, job *pyramidJob) error {
 		draw.Draw(scratch, r, img, sr.Min, draw.Src)
 	}
 
-	resized := resize.Resize(256, 256, scratch, resize.Lanczos3)
+	if err := conv.Convert(resized, scratch); err != nil {
+		return err
+	}
 
 	log.Printf("Writing pyramid tile '%s'.\n", job.dst)
 
@@ -177,9 +179,22 @@ func fuseTile(scratch *image.RGBA, job *pyramidJob) error {
 func fuseTiles(jobs chan pyramidJob, done *sync.WaitGroup) {
 	defer done.Done()
 	scratch := image.NewRGBA(image.Rect(0, 0, 512, 512))
+	resized := image.NewRGBA(image.Rect(0, 0, 256, 256))
+
+	cfg, err := rez.PrepareConversion(resized, scratch)
+	if err != nil {
+		log.Printf("WARN: cannot prepare rescaling: %s\n", err)
+		return
+	}
+
+	conv, err := rez.NewConverter(cfg, common.ResizeFilter)
+	if err != nil {
+		log.Printf("WARN: Cannot create image converter: %s\n", err)
+		return
+	}
 
 	for job := range jobs {
-		if err := fuseTile(scratch, &job); err != nil {
+		if err := fuseTile(scratch, resized, conv, &job); err != nil {
 			log.Printf("WARN: Writing image failed: %s\n", err)
 		}
 	}

cmd/mtwebmapper/tilesupdater.go

@@ -6,7 +6,6 @@ package main
 
 import (
 	"encoding/json"
-	"fmt"
 	"image"
 	"image/draw"
 	"log"
@@ -17,7 +16,7 @@ import (
 	"strings"
 	"sync"
 
-	"github.com/nfnt/resize"
+	"github.com/bamiaux/rez"
 
 	"bytes"
 
@@ -215,9 +214,10 @@ func (tu *tileUpdater) doUpdates() {
 func updatePyramidTiles(level int, baseDir string, jobs chan xzm, done *sync.WaitGroup) {
 	defer done.Done()
 	scratch := image.NewRGBA(image.Rect(0, 0, 256, 256))
+	resized := image.NewRGBA(image.Rect(0, 0, 128, 128))
 
 	for job := range jobs {
-		if err := updatePyramidTile(scratch, level, baseDir, job); err != nil {
+		if err := updatePyramidTile(scratch, resized, level, baseDir, job); err != nil {
 			log.Printf("Updating pyramid tile failed: %s\n", err)
 		}
 	}
@@ -243,7 +243,7 @@ var ofs = [4][2]int{
 
 var windowSize = image.Pt(128, 128)
 
-func updatePyramidTile(scratch *image.RGBA, level int, baseDir string, j xzm) error {
+func updatePyramidTile(scratch, resized *image.RGBA, level int, baseDir string, j xzm) error {
 
 	var orig image.Image
 
@@ -251,8 +251,9 @@ func updatePyramidTile(scratch *image.RGBA, level int, baseDir string, j xzm) er
 		baseDir,
 		strconv.Itoa(level),
 		strconv.Itoa(int(j.P.X)),
-		fmt.Sprintf("%d.png", j.P.Z))
+		strconv.Itoa(int(j.P.Z))+".png")
 
+	sr := resized.Bounds()
 	for i := uint16(0); i < 4; i++ {
 		if j.Mask&(1<<i) != 0 {
 			//log.Printf("level %d: modified %d\n", level, i)
@@ -264,10 +265,11 @@ func updatePyramidTile(scratch *image.RGBA, level int, baseDir string, j xzm) er
 				strconv.Itoa(bx+o[0]),
 				strconv.Itoa(bz+o[1])+".png")
 			img := common.LoadPNG(path)
-			img = resize.Resize(128, 128, img, resize.Lanczos3)
-			sr := img.Bounds()
+			if err := rez.Convert(resized, img, common.ResizeFilter); err != nil {
+				return err
+			}
 			r := sr.Sub(sr.Min).Add(dps[i])
-			draw.Draw(scratch, r, img, sr.Min, draw.Src)
+			draw.Draw(scratch, r, resized, sr.Min, draw.Src)
 		} else {
 			// Load lazy
 			if orig == nil {