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