Image Editing with 30-bit Monitors

Payable hardware for professionals is capable of 30-bit throughput since quite some years. And costs continue to go down. This means even budget setups are possible with this kind of gear. So lets follow the question why, who and how monitors capable of displaying 30-bit alias 10-bit per red, green and blue channel can be used. This blog article will first touch some basics, followed by technical aspects below.

Why is it useful to display graphics on a 30-bit monitor setup?
It is essential for graphical editing, to see what effect a editing step has. It is pretty common that low resolution monitors impose a barrier to reliably predict the intended output. This is true for geometrical resolution like for colour resolution and for gamut. The rule of thumb is, the graphics editor needs the most information available to do here/his job and spot artefacts and issues early in the process. This principle is deployed for print, web, film and video editing to reduce costs. You know, redoing something costs time and is part of the jobs calculation. More image information means as well more certainty to reach a graphical result. The typical artefact caused by low colour resolution is reduced tonal range. Colour conversions can reduce the tonal range further. So a sRGB image will look different on a 8-bit per channel monitor with a native gamma close to 2.2 compared to a pipeline with 10-bit per channel. The 8-bit output imposes a bottleneck resulting in loosing some tonal steps known as banding, which must not necessarily be present in the observed sRGB image. One very often read argument against higher bit depth is, that editing hardware shall be as close as possible to customers ones. But that is a illusion. The wide diversity of media and devices makes this nearly impossible. But simulation of end customer hardware is of course an issue and many graphics software has implemented simulation capabilities to address that concern.

Who is most interested in 30-bit colour editing on Linux?
Graphics professional and ambitious users closely observe Linux since many years and deploy it. Many block busters are produced and rendered on Linux machines. Web graphics is well supported since years and camera raw programs implemented a impressive level of features in the last years. So Linux is a potential content creation platform beside content consumption. The typical work flow for content creating people is to generate and edit their art work in high geometrical and colour resolution and down convert to lower resolutions as fits for the job, be that web, print, catalog previews and more flexible high quality delivery depending on actual contract. For instance many photographers archive their shootings in the cameras native format to preserve all available information for later editing or improved rendering. This is a important investment in the future for non short lived work, where old files can shine in new light. Motion picture productions are often rendered and color graded in floating point space by using the OpenEXR intermediate file format and output to 12 bits per component for playback in a cinema. Video production uses in parts raw workflows for advertisements. Medical-, scientific- and archival imaging are potentially interested too and require in parts 30-bit setups like in the DICOM standard. The benefit of 10-bit per channel versus 8-bit does not matter to everyone. Most consumers will not spot any difference while watching web video. But in more demanding areas it is a small but helpful improvement.

How to deploy 30-bit displays on Linux?
That feature was implemented by several companies starting on low level software components like X11, Cairo and pixman. However desktops where pretty slow to adapt software to the new needs and fix bugs. That was in part of the initially higher costs for the hardware. Only few developers in the open source community had early access to suitable gear. I do not write here about suitable graphic cards and monitor combinations. You should consult the web for this. Search for 30-bit monitor. Many early adopters observed psychedelic colours, not working graphics areas and more. Here the state on the well known KDE X11 desktop in release 4.11 on a openSUSE-13.1 . The login screen colours are broken. The splash screen after login looks correct and after some period the desktop becomes visible with again broken colours. To manually fix most of that, one have to tell that Qt shall use native colours. Create following text into a file called ~/.kde4/env/qtnative.sh .

$ kwrite ~/.kde4/env/qtnative.sh

#!/bin/sh
export QT_GRAPHICSSYSTEM=native

With the above variable the desktop should look reasonably in KWin, which is really great. Automating that in Qt would be appreciated.

However 30-bit monitors typical aim at high quality setups. Beside colour resolution they often enough offer a wider gamut than usual monitors. This results in partially heavily saturated colours, which burns in sensible eyes. Those people who do colour grading or photo editing are mostly affected, otherwise they can not easily play this work. So desktop colour correction is an other important feature to enable here. KWin supports ICC based colour correction through KolorManager, which would be useful for the colour saturation. But KWin disables all effects for 30-bit OpenGL visuals. The alternative Compiz-0.8 series has the CompIcc colour server plug-in, which provides the same ICC colour correction feature. To make use of it, one needs to install following packages: compizconfig-settings-manager, CompIcc-0.8.9. Unfortunedly the KDE decorator is no longer available. So use the Emerald decorator from X11:Compiz with the 30-bit-shadow.patch in order to avoid artefacts in the shadow code. Compiz can be used as a default window manager application. Use the system settings to switch to Compiz. Use ccsm to switch on Color Management if not done automatically. And voila the 30-bit desktop should be ready to explore.

What works and what not?
The Plasma desktop is fine including all menus. Dolphin, KWrite, and other applications work. Thunderbird shows some artefacts due to not properly supporting the R10G10B10A2 pixel format. The same is true for Firefox, which lets in parts shine through content behind the Firefox window. Gwenview and ShowFoto work fine within their 8-bit drawing. Only the preview is broken in ShowFoto. Krita supports with the OpenGL backend even native 10-bit per colour component. Menus in Sketch are black. Krita shows minimal artefacts through twice colour converting from image to sRGB by Krita and from sRGB to the monitor colour space by CompIcc. But this effect is much lesser visible than the improvements through its 30-bit support. Applications which try to code 24-bit colour themselves are broken like Konqueror. Gtk and hence Gnome applications with graphical areas do not work. They show black areas. VLC works fine. So daily work should be fine in with 30-bit in the KDE application family depending what you do, with some minor glitches. Valuable Gtk applications as is like Inkscape and most Gtk applications are unusable in a 30-bit setup, with Gimps drawing area being a exception. Thunderbird/Firefox are guessedly affected by the same Gtk bug for which a patch was created some time ago. A patched libgtk-2 is available for testing on openSUSE, which appears to have fixed the problem almost for me.

Beside the need to exchange a windowmanager, to patch a few components and do some manual settings, Linux appears almost there in support of 30-bit setups. Polishing of that feature needs testing of patches and finally acceptance for distribution. Your feedback about bugs, tests and patches can make a difference to developers.

Oyranos-0.9.0 released

The first beta of the object oriented C API came out end of last month. It brings a bunch of changes. First, all known Oyranos using projects are updated or have patches available. While the internal changes where heavy weight, most external users had few lines to change. The new APIs where possible through a Google Summer of Code project of Yiannis Belias in  2011. Nearly all C object types and basic functions are generated from django templates, which are interpreted and  processed by the Grantlee engine and a customising plugin.

As we work on WM ICC colour management, we need more facilities to test workflows. In order to support that, the oyranos-icc tool was added and can generate 3D LUTs in various formats. Among them is hald and 3D texture. Te later format is used in CompICC and the new KolorServer of Casian Andrei. The 3D texture is stored as a PPM and can be loaded into the image_display example viewer and drives fast client side colour correction inside OpenGL. The same tool can be used to convert PPM and PNG files through ICC profiles including proofing and effect profiles, much like the C API allows.

The oyranos-profile-graph tool was already described in this blog. New is the generation of ICC profiles out of libRaw/dcraw camera matrices. That is a very nice fallback in case a camera RAW file has no custom profile available. This will not substitute DCP profiles, but is a step forward in integrating camera RAW workflows into ICC driven systems.

default ROMM RGB versus dcraw matrix derived colour space ICC profiles

 

 

OpenICC Google Summer of Code 2012 results

Google Summer of Code

Participation of the OpenICC group in the Google Summer of Code 2012 program was this year a great success. All projects reached their respective goals. Here a small summary:

Colour Management for Krita Printing
Joseph Simon worked on adaption and integration of his last years implementation for colour managed printing into Krita/Linux. The workflow is based on ICC profile injection into PDF through the means of a OutputIntent.

KWin Colour Correction
Casian Andrei’s KWin changes for ICC style colour correction in the GPU are reviewed upstream and his new code to the KolorManager code base waits just for approval. The concept follows the X Color Management spec. In contrast to the elder CompICC implementation is the KWin result highly modular and thus very flexible.

Simple Toolkit Abstraction
Nitin Chadas SimpleUI project for rendering a subset of XForms was written from
ground up and provides now backends for FLTK, Gtk and Qt. It needs a bit
of polishing to become useable.

Thanks to Google for providing the colour management and graphics community again a great chance to code and learn the open source way.

CompICC-0.8.5 released

A new version of the compiz plugin for ICC colour correction of monitors is released. This release is a feature release.

Changes Overview:

  • new support per region ICC profiles
  • new switch to X Color Management specification
  • require libXcm-0.5.0 and Oyranos-0.4.0

Changes from 0.8.4:

  • fix alpha blending
  • speed up load time (cache the transformed pixels in memory)

About:
The project brings you instant desktop colour correction on GPU through the compiz window manager (0.7.x/0.8.x). It supports multi monitors and live connecting. The implicite colour conversion appears on the fly. To opt out of colour correction for specialised graphics applications the X Color Management spec 0.4 is supported. Devices can be configured through the Oyranos Colour Management System.

ChangeLog:
http://compicc.git.sourceforge.net/git/gitweb.cgi?p=compicc/compicc;a=shortlog;h=refs/tags/0.8.5

git git://compicc.git.sourceforge.net/gitroot/compicc/compicc
git sha1: c963bdbc7aa4bf9703f3c87f82734d1223ff7d63
package: http://downloads.sourceforge.net/project/compicc/Compicc/compicc-0.8.5.tar.bz2
size: 76548 Byte
sha1sum: 902f2ea6b9c0aabe91297f6b80dd1f5ef9f910d1 compicc-0.8.5.tar.bz2
md5sum: 41a1a08c82ee18025d535c3dbc86aaf8 compicc-0.8.5.tar.bz2
Linux RPM: http://download.opensuse.org/repositories/multimedia:/color_management/

X Color Management 0.4 DRAFT1

Some days ago on FOSDEM I gave a presentation about Colour Management in Compositors. At that point is was not very clear how to introduce colour management especially into the upcoming Wayland display server core and thus make it wide spread. The answer from Wayland developers is the same as from Xorg ones. They want a small core and colour management does not fit inside this.

As a result of a discussion between several colour management interested people from wayland, toolkits and me on the wayland IRC channel, we found a smallest common denominator. That will be a per window colour correction mechanism. The advantage is, it will be very easy to implement inside compositors and they can even start today about ICC support. The biggest disadvantage for applications is, they need to colour correct the whole window. That is as well the reason, why I did not like the idea in the past. Anyway, hopefully toolkits will jump in at one point and make that easy. Meanwhile we need to focus on example code, which demonstrates how per window colour correction can work.

The spec can be found as usual in the libXcm git repository. The main new part is the _ICC_COLOR_OUTPUTS atom and XcolorOutput structure.

OpenICC Program FOSDEM 4 + 5 February 2012 in Brussels, Belgium

OpenICC uses 2012 a DevRoom at FOSDEM on Sunday together with Xorg people. The goal is to provide a meeting space for colour management topics.

The program is online on the OpenICC wiki. The talks will present and discuss colour management in Compositors, OpenICC, Scribus, Taxi DB, Oyranos and SVG2.

Oyranos Colour Management LiveCD III

The third version of the Oyranos Colour Management LiveCD is based on openSUSE-12.1 and will run on x86_64 compatible PC´s. I placed the ISO image yesterday after some preparations on the better accessible SourceForge site for download. The CD project starts into a instantly colour managed desktop, which is unique under Linux.

The ICC desktop colour correction is done by the CompICC colour server. The LiveCD contains the usual mixture of colour managed graphics applications. Among them is the colour management system Oyranos, the KDE Color Management panel, a profiler based on Argyll CMS and many colour management aware applications for drawing, colour analysis and desktop publishing. Due to package size changes not even all programs from the last release are covered. I am very sorry for that. Nevertheless I decided to include Firefox, as a very wide spread every days application. After fixing a bug in Firefox, the web browser is usable under CompICC and has generally improved regarding colour management. But still it has many colour management related issues.

The desktop widget contains some test images to help you verifying, your desktop is setup correctly and works inside all colour managed applications. Covered are some JPEG, PNG, TIFF and SVG images with wide gamut and swapped channel test profiles. You will surely spot problems, as not everything in Linux desktops is really polished regarding colour management. But these test data can help you in getting a sense of, what can be relied on and what not. You can easily include other applications into your test by installing from openSUSE. And please help the projects and report bugs to the according project bug trackers. This will show interest in the issues seen with colour management and helps developers spot current weaknesses, which are otherwise overseen.

The CD uses the stable version of the Compiz compositing window manager, which is the only one being able to run under KDE. While the Oyranos CMS is packaged in openSUSE, a full screen desktop colour correction is currently not possible with KDE´s KWin or any window manager other than Compiz with the CompICC plugin. One difference to the previous LiveCD is a better useable nouveau driver, which since greatly improved and can now launch into Compiz with GPU acceleration.

KDE and Colour Management

Colour Management has a long way to come to the Linux desktop. Like on other computing environments first came single applications like Scribus, CinePaint or Krita and proved colour management be useful and mature. Now the open source Desktop stacks are following. Most advanced and wide spread inside colour managed applications is colour correction for monitors.

For KDE exists the KolorManager systemsettings panel for configuring a ICC profile per monitor device. It´s Oyranos CMS cares as well about setup of standard Xorg _ICC_PROFILE(_xxx) root window atoms and video card graphics table (VCGT). The later is a one dimensional per channel colour correction feature. So expect no magic all included solution by this means.

The heart of today most wide spread colour management systems is the ICC file specification. And to get ICC style Colour Management working inside KDE, the framework has to handle several needs.

One is to provide a overall desktop colour correction, which applies to the whole monitor screen area. A Desktop Colour Server will improve the overall Desktop usability and appearance in heterogeneous  environments like Linux. Obviously colour measurement devices and early colour correcting applications need native access to the monitor colour space. The currently only full featured and backward compatible implementation of that scheme for Linux is the CompICC plugin to Compiz. The CompICC colour server assumes sRGB for all input. Output target is the actual monitor profile set e.g. by KolorManager. More details can be read in a older blog post. Given that colour servers are still pretty rare, only osX and CompICC provide that, it might not be a good goal for the foreseeable future to let all applications rely solely on that feature for their colour corrections. But it has the potential to the most slick and flexible desktop colour experience.

On the Input side ICC profiles and according Exif meta data need to be detected from the input streams and get appropriately assigned as ICC meta data to graphics objects. That can be application specific but is a very common task, which will be better implemented on the toolkit or framework level. The display component should then make use of this ICC meta data and do on the fly colour correction. As well file output needs support of embedding the ICC profile data back into the data stream.

Alongside the ICC data handling come options and preference management, which is covered by the KolorManager GUI to the Oyranos API.

X Color Management 0.3 DRAFT1

The net-color spec from the libXcm repository is renamed. During a great conversation with Martin Gräßlin from KWin at oSC rwx³ he pointed out, that the _NET_ prefix is reserved inside the Xorg atom name space. So I decided to rename all atoms in the applications known to me, which use the net-color spec. The renaming went on fast and all apps work again as expected in git.

The new spec is called X Color Management. It contains the color regions in Xorg description and the used device profile for Linux desktop colour servers.
Affected are libXcm, Xcm, Oyranos, CompICC and CinePaint.

Oyranos @ rwx³

rwx³ alias openSUSE Conference (oSC) will be from 11.09. – 14.09.2011 in Nuremberg / Germany. Im going the to openSUSE Conference! The conference for openSUSE - and Free Software enthusiasts, September in Nuremberg, Germany. Are you? We will meet there and can discuss ICC colour management for the openSUSE distribution, KDE and Qt.

Sebastian Oliva will be there too. I hope we can hack together a Oyranos connection to his newly created ICC DB. The ICC DB project, done during GSoC 2011, shall be used to search for ICC profiles by terms of colour device configurations. This means a printer can obtain a fitting ICC profile for a special driver without the need to have all the canned profiles packaged. Independent vendors can easily upload their ICC data and get their optimised profile selected automatically – if all works. Sebastian and Joseph Simon have done fair bits to get there in a clean way, without hacking the whole system.

I will have colour measurement equipment with me and we can create new profiles for actual used gear, like laptop monitors. Of course these shall walk into the ICC DB.

It would be cool to meet with Compiz and KWin maintainers/packagers to get the GPU colour managed desktop project further. The net-color-spec appears pretty robust. But we need a critical mass to support the concept of colour correcting all windows on the desktop in compositing window managers.

Will be great to meet you all.