Obtain the number of CPUs / cores in Linux / bash

grep -c ^processor /proc/cpuinfo 

Src:http://stackoverflow.com/questions/6481005/obtain-the-number-of-cpus-cores-in-linux 

Inkscape - change the color of markers

How do I change the color of markers (e.g., arrow ends)?

By default, markers are black. You can change their color to match the color of the stroke of the object they are applied to by enabling an effect: Extensions > Modify Path > Color Markers to Match Stroke. 

http://wiki.inkscape.org/wiki/index.php/Frequently_asked_questions#How_do_I_change_the_color_of_markers_.28e.g..2C_arrow_ends.29.3F

Adding alpha (transparent) background to jpeg images, logos

- Some posters, powerpoints, have non-white backgrounds. Company logos with transparency look nicer on these. However, sometimes logos are only available in the jpeg format.

- Tools like GIMP/KolourPaint will easily flood-fill the white as alpha, except for the closed figures like "O,e" letters. This can be done by hand, than the result saved as png with alpha channel.

- However, jpeg images are full of shades of white, so the result can be very messy sometimes.

- Solution: use advanced software such as ImageJ, to change the contrast so any intensity value say, above 250/255, will be brought to 255. Then automatic flood-fill of the other software programs will be a lot more efficient.

Note: as of 03/2015, ImageJ does not natively support the alpha channel, so other paint software is still required to finish the job.

bash merge multiple pdf files

A) Using mutool

apt-get install mupdf-tools

mutool merge [options] file1 [pages] file2 [pages] ...

Options:

-o output

The output filename.

-O options

See mutool create for details on this option. 

 

Source: https://mupdf.com/docs/manual-mutool-merge.html

B) Using pdfunite. If needed, install poppler package

example uses:

pdfunite in-1.pdf in-2.pdf in-n.pdf out.pdf

pdfunite *.pdf out.pdf

Src:http://stackoverflow.com/questions/2507766/merge-convert-multiple-pdf-files-into-one-pdf

bibtex medphys aapm enquote error

- when using the custom home-brew style medphys.bst
- after pasting the pre-compiled bibliography
- if the compilation crashes and says, \enqoute() already defined,
- you simply forgot to comment out \bibliographystyle(medphys)

convert bunch of images to video using ffmpeg

sample code:

avconv -framerate 7 -i img%03d.png -qscale 1 -c:v libx264 -pix_fmt yuv420p out.mp4

-use avconv, cause ffmpeg command is deprecated
-framerate is the desired visual result in fps units, can be a fraction like 1/5
-i is the regexp to retrieve pics
-qscale is quality: 1 for best, 31 for worst
-c:v is the video codec
-pix_fmt is the color space setting, yuv240p is the most portable
NOTE: the order of the arguments is important: some come before -i, some after -i


Src: https://trac.ffmpeg.org/wiki/Create%20a%20video%20slideshow%20from%20images

keywords: video, mpg, mpeg, mp4, movie, film

install ffmpeg video tool

sudo apt-get install ffmpeg

sudo apt-get install libavcodec-extra-53
sudo apt-get install libavcodec-extra57

Src: http://ubuntuforums.org/showthread.php?t=200562
keywords: video, mpg, mpeg, mp4, movie, film