+jpgs=()
+pngs=()
+ppms_jxl=()
+ppms_webp=()
+for img ($imgs) {
+ [[ -r info/$img.img ]]
+ if [[ $img:e = jxl ]] ; then
+ [[ -r alt/$img.jpg ]] || [[ -r alt/$img.png ]] && : || {
+ grep -q "JPEG bitstream reconstruction" info/$img.img &&
+ jpgs=($jpgs $img) || pngs=($pngs $img)
+ }
+ [[ -r preview/$img.webp ]] || ppms_jxl=($ppms_jxl $img)
+ else
+ [[ -r preview/$img.webp ]] || ppms_webp=($ppms_webp $img)
+ fi
+}
+
+[[ ${#jpgs} == 0 ]] || {
+ echo JPEG reconstruction... >&2
+ parallel "djxl --quiet {} alt/{}.jpg && touch -r {} alt/{}.jpg" ::: $jpgs
+}
+jpgs=()
+
+[[ ${#pngs} == 0 ]] || {
+ echo PNG generation... >&2
+ parallel "${0:h}/djxl2ppm {}" ::: $pngs
+ parallel "pamtopng < {}.ppm > {}.png && rm {}.ppm" ::: $pngs
+ parallel "pngcrush -warn -rem alla -rem allb -z 2 {}.png alt/{}.png && rm {}.png" ::: $pngs
+ parallel "advpng --quiet --recompress -4 alt/{}.png && touch -r {} alt/{}.png" ::: $pngs
+}
+pngs=()
+
+[[ ${#ppms_jxl} == 0 ]] || {
+ echo JPEG XL decompression for preview... >&2
+ parallel "${0:h}/djxl2ppm {}" ::: $ppms_jxl
+}
+[[ ${#ppms_webp} == 0 ]] || {
+ echo WebP decompression for preview... >&2
+ parallel "dwebp {} -ppm -o {}.ppm" ::: $ppms_webp
+}
+ppms=($ppms_jxl $ppms_webp)
+[[ ${#ppms} == 0 ]] || {
+ echo Preview scaling and WebP compression... >&2
+ parallel "pnmscale -w 100 < {}.ppm > {}.ppm.ppm && mv {}.ppm.ppm {}.ppm && cwebp -quiet -pass 10 -alpha_filter best -m 6 -o preview/{}.webp {}.ppm && rm {}.ppm && touch -r {} preview/{}.webp" ::: $ppms
+}
+ppms_jxl=()
+ppms_webp=()
+ppms=()
+