Added notes about ghostscript to the KB

knowledge base/ghostscript.md

@@ -0,0 +1,42 @@
+# Ghostscript
+
+## TL;DR
+
+```sh
+# Install.
+brew install ghostscript
+sudo port install ghostscript
+
+# Reduce the size of PDF files.
+gs -dNOPAUSE -dQUIET -dBATCH \
+  -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -dCompatibilityLevel=1.4 \
+  -sOutputFile=path/to/small/file.pdf \
+  path/to/massive/file.pdf
+```
+
+## Reduce the size of PDF files
+
+Execute the following:
+
+```sh
+gs -dNOPAUSE -dQUIET -dBATCH \
+  -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -dCompatibilityLevel=1.4 \
+  -sOutputFile=path/to/small/file.pdf \
+  path/to/massive/file.pdf
+```
+
+Use one of the following options for the value of `-dPDFSETTINGS`:
+
+| Value       | Description                                    |
+| ----------- | ---------------------------------------------- |
+| `/screen`   | Screen-view-only quality, 72 dpi images        |
+| `/ebook`    | Low quality, 150 dpi images                    |
+| `/printer`  | High quality, 300 dpi images                   |
+| `/prepress` | High quality, color preserving, 300 dpi images |
+| `/default`  | Almost identical to `/screen`                  |
+
+## Sources
+
+- [Reducing PDF File size]
+
+[reducing pdf file size]: https://superuser.com/questions/293856/reducing-pdf-file-size#1217306

knowledge base/mac os x.md

@@ -143,13 +143,10 @@ defaults write com.apple.finder AppleShowAllFiles TRUE
 
 ## Resize an image from CLI
 
-Note:
-
-* edits the input image
-* `-Z` retains ratio
-
 ```sh
-sips -Z 1000 Downloads/IMG_20190527_013903.jpg
+# Retain ratio.
+# Save as different file.
+sips -Z 1000 -o resized.jpg IMG_20190527_013903.jpg
 ```
 
 ## Boot keys cheatsheet