Imagemagick Nconvert Resize Photos Images
http://www.imagemagick.org/Usage/
Mass resize
jpg to useful size (replace):
mogrify -verbose -format jpg -auto-orient -resize 2048x2048 -compress JPEG -quality 90 *.jpg
combine all images in directory into pdf:
img2pdf *.jpg --output combined.pdf
resize jpgs while recursing into subdirectories
find . -name "*.jpg" | xargs mogrify -verbose -format jpg -auto-orient -resize 66% -compress JPEG -quality 90
If you want to restory the file modification date afterwards:
exiftool '-FileModifyDate<DateTimeOriginal' -r -v -ext jpg .
other stuff:
mogrify -path small -auto-orient -sample 860x574 -compress JPEG -quality 80 *.*
mogrify -format jpg -auto-orient -strip -compress JPEG -quality 80 *.*
mogrify -format png -auto-orient -strip -resize 64x64 *.png
resize gives better quality than sample, but is slower
Make background color transparent
Simple color replacement
convert input.png -transparent white output.png
Pretty good, flood fill with fuzz percentage
convert input.png -bordercolor white -border 1x1 -alpha set -channel RGBA -fuzz 5% -fill none -floodfill +0+0 white -shave 1x1 output.png
For multiple images
mogrify -path modified_images -format png -bordercolor white -border 1x1 -alpha set -channel RGBA -fuzz 5% -fill none -floodfill +0+0 white -shave 1x1 *.jpg
Useful Addition: -trim to remove unnecessary border
Strip color profile information
mogrify -format png -strip *.png