Playing with YUV colour space from command line

I wanted to get familiar with the YUV colour space, and the direction of U/V axes used in common video formats.

A bash one-liner made it easy for me to input colour values and preview them:

while true; do read -p "Y: " y && read -p "U: " u && read -p "V: " v && perl -e "print '$y' x 4096; print '$u' x 1024; print '$v' x 1024;" | xxd -r -ps | ffplay -f rawvideo -pix_fmt yuv420p -s 64x64 - ; done

Breaking this ad-hoc one-liner down into parts:

#!/bin/bash

set -e

echo "Enter Y/U/V values as two-char hex-byte value e.g. 3f"

# Loop until user hits Ctrl+C
while true
do

  # Read colour co-ordinates
  read -p "Y: " y
  read -p "U: " u
  read -p "V: " v

  # Generate hex of a 64x64-pixel image frame in YUV420p encoding, un-hex it, display it on screen with FFMPEG
  perl -e "print '$y' x 4096; print '$u' x 1024; print '$v' x 1024;" | \
    xxd -r -ps | \
    ffplay -f rawvideo -pix_fmt yuv420p -s 64x64 -

done

Great ūüôā

Photography: post-processing – and some amazing free, open-source software workflows

Introduction

This article describes some free, open-source photo/video processing software that I use since I moved from Windows to Linux. ¬†Most of this software also runs on Windows, and it is also free. ¬†As much as I like Adobe CS5 and Sony Vegas, I would struggle to move back to them (excluding Illustrator/InDesign) now that I’ve got used to the open-source offerings.

If you are comfortable with building programs from the source (or use Arch Linux, which makes this really really easy) then do so and you could get significant performance improvements on modern processors. ¬†Unlike the somewhat expensive offerings from Adobe, these open-source programs don’t install nasty viruses on your PC*.

* Some¬†Adobe products (when legally purchased) come with a rootkit virus called “FlexNet” which can cause data-loss and corrupt boot-loaders (making systems unbootable). ¬†Amusingly, the pirate copies of Adobe’s products generally have this virus removed from them. ¬†That’s how I wasted over ¬£100 by buying Adobe software, only to end up using a pirate copy…

Photo processing on Linux

Before I left the UK, I ran on Arch Linux. ¬†When travelling, I boot public PCs with Debian from my phone via DriveDroid. ¬†This means that Photoshop and Lightroom are not available for me to use in my photography workflow, as they are amongst the few programs that can’t be run in Linux via Wine.

This isn’t much of a problem though, as the open-source offerings for photography are generally very powerful and well maintained. ¬†They have a steeper learning curve than Adobe’s products, but allow you to do more in less time when you get used to them.

When mentioning open-source image-editing software, people usually think of “The GIMP“, which is probably the ugliest piece of software I have ever seen (even if I include commercial scientific software). ¬†Its numerous text-rendering issues (on all operating systems) make it generally a pain to work with. ¬†Running an old version of PaintShop Pro or PhotoDeluxe under Wine is preferable to using The GIMP, despite PSP being incredibly buggy and PD being ancient. ¬†Thankfully, there are many alternative free/open-source image processing programs available which are powerful, consistent and usable.

On the camera

On the camera, I would love to use some custom firmware similar to Magic Lantern, which is available for Canon DSLRs. ¬†I suppose I can wait for Vitaliy Kiselev’s hack to expand and mature. ¬†For lack of this, I just shoot RAW in the usual ways, using the standard delay/repeat/timelapse/remote/long-exposure features.

Cataloging and RAW processing

After taking the RAW files off my camera, I first catalogue and process them with RawTherapee. ¬†I hear that there is a stable Windows port of this program available too. ¬†RawTherapee has the best noise-reduction that I have come across yet, has brilliant colour correction, and makes batch processing effortless (which should be a minimum requirement for RAW processing software). ¬†The only downside is that it can not read the white-balance setting from Nikon’s RAW files, but this is because Nikon encrypt that data it in an attempt to force their slow, unstable, bug-ridden ViewNX/CaptureNX upon people.

If I just want to process a load of files with the same processing settings, then I can use RawTherapee’s batch processing although for simple jobs I often use ImageMagick instead.

Video processing

For video processing I’ll use Kdenlive¬†(which has completely replaced Sony Vegas for me). ¬†As for time-lapses, I’ll usually stick to ffmpeg¬†or slowmoVideo, the latter being pretty powerful – it supports non-linear time flow, optical flow interpolation, and optical-flow driven motion-blur.

HDR

HDR? ¬†What HDR? ¬†I probably should start learning this style, as it does produce some really nice results when people take the time to do it properly (i.e. go beyond just “pressing the HDR button”).

Post

As a general rule, I only use effects which operate “globally”, i.e. to the whole image. ¬†If an effect requires me to click on the actual image, then I won’t use it (excluding crop). ¬†This is just a personal rule to prevent me from spending hours on a single image, developing amazing art¬†like some others do. ¬†I occasionally break this rule to clone out annoying people,¬†parked cars, or lens flares¬†but this is quite rare.

Summary

There’s lots of cool free/open-source image processing software out there. ¬†Get rid of any bad impressions that you might have from The GIMP and branch out into the purpose-built software. ¬†The learning curves are steep, but the rewards are greater. ¬†A list of software mentioned is given below:

  • The GIMP¬†– included for completeness, but DO NOT USE this unless you hate yourself.
  • Magic Lantern¬†– Like CHDK, but for Canon DSLRs.
  • Vitaliy Kiselev’s hack¬†– Like CHDK but for Nikon DSLRs. ¬†I haven’t tried this yet.
  • RawTherapee¬†– RAW processing and batch-processing software with the best noise-reduction I’ve come across yet.
  • ImageMagick¬†– command-line image processing, useful for automated tasks and batch processing, e.g. resize to fixed width and watermark all images.
  • Kdenlive¬†– Powerful non-linear video editor with great shake-reduction.
  • ffmpeg¬†– command-line video processing, Debian users will probably have the libav fork instead.
  • slowmoVideo¬†– very good timelapse/slowmotion software supporting non-linear time flow, optical flow interpolation and nice motion blur.
  • DriveDroid¬†– not free/open-source but useful when travelling: it allows me to boot Arch Linux onto any hostel PC from my Android phone, and have a personal desktop complete with all my software.

All of these programs also work on Windows 2003, excluding the camera firmwares and also DriveDroid which is a mobile Android app.