script for " turn the pdf to img with compression".
some code are borrowed from this url
most scripts need GhostScript 9.26, you can find it on here
cropimg.m : crop imgs for a folder
pdf2img: convert pdf to imgs(most of formats of image)
compress_pdf.m: compress the pdf with user-defined dpi, you can change the parameter 'xxxxResolution'
remove the background, please refer to this link