Category Archives: Image Technologies

Color Gamut

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CIExy1931

In color reproduction, the color gamut is a complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a certain output device. The term gamut was adopted from the field of music, where it means the set of pitches of which musical melodies are composed.

Generally, the color gamut is specified in the hue–saturation plane, as many systems can produce colors over a wide intensity range within their color gamut; in addition, for subtractive color systems, such as printing, the range of intensity available in the system is for the most part meaningless outside the context of its illumination. When certain colors cannot be displayed within a particular color model, those colors are said to be out of gamut.

While processing a digital image, the most convenient color model used is the RGB model. Printing the image requires transforming the image from the original RGB color space to the printer’s CMYK color space. During this process, the colors from the RGB which are out of gamut must be  converted to values within the CMYK space gamut (gamut mapping).

There are several reasonable strategies for performing gamut mappings, these are called rendering intents. Four particular strategies were defined by the International Color Consortium (ICC), with the following names : Absolute Colormetric, Relative Colormetric, Perceptual, Saturation.

Gamuts are commonly represented as areas in the CIE 1931 chromaticity diagram. The accessible gamut depends on the brightness; a full gamut must therefore be represented in 3D space. Systems that use additive color processes usually have a color gamut which is roughly a convex polygon in the hue-saturation plane.

A list of representative color systems ordered from large to small color gamut is shown hereafter :

  • Laser video projector
  • Photographic film
  • CRT Monitor
  • LCD Monitor
  • Television
  • Painting
  • Printing

An interactive Flash demo explaining color gamut mapping is available at the website of the Stanford University. Gamutvision, an gamut viewer, is available from Imatest LCC (Norman Koren).

Different color spaces have been defined for digital image processing : RGB, LAB, CMYK. The sRGB IEC-61966-2.1 color space was conceived as a multipurpose color space standard for consumer digital devices (s stands for standard in sRGB). Other RGB color spaces are Apple RGB, ColorMatch RGB, ProPhoto RGB, Adobe RGB (1988) and PhotGamutRGB. A comparison between sRGB and Adobe RGB is shown at the website of Cambridge in Colour.

DNG : Digital Negative, camera raw data format

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Last update : January 7, 2016

DNG

Digital Negative

Digital Negative (DNG) is an public archival open raw image format owned by Adobe used for digital photography. It was launched in 2004. DNG is based on the TIFF/EP standard format, and mandates significant use of metadata. Exploitation of the file format is royalty free.

Adobe provides the Digital Negative Specification, a free Adobe DNG Converter (version 6.3), which easily translates raw files from many of today’s popular cameras, an SDK (Software Development Kit) and an DNG Profile Editor.

DNG is supported by various camera providers  and photographic software developers (Adobe Photoshop, Adobe Lightroom, …). DNG is also supported by ExifTool, a platform-independent Perl library plus a command-line application for reading, writing and editing meta information in a wide variety of files, developed by Phil Harvey. ExifTool is also available as a stand-alone Windows executable and a Macintosh OS X package. The current version is 10.09 published on January 4, 2016.

Exif, IPTC, XMP

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Last update : August 25, 2013

Exif (Exchangeable image file format) is a specification for the image file format used by digital cameras and scanners. The specification uses the existing JPEG, TIFF Rev. 6.0, and RIFF WAV file formats, with the addition of specific metadata tags. It is not supported in JPEG 2000, PNG, or GIF.

Exif was created by the Japan Electronic Industries Development Association (JEIDA).

The metadata tags defined in the Exif standard cover a broad spectrum :

  • Date and time information
  • Camera settings (camera model and make, orientation, aperture, shutter speed, focal length, metering mode, ISO speed, …)
  • Thumbnails for previewing the picture
  • Geolocation
  • Descriptions
  • Copyright

The most used tool to edit Exif informations is the ExifTool by Phil Harvey. Another very useful tool is PhotoME (Photo Metadata Editor) developped by Jens Duttke which handles also embedded color (.icc) profiles.

There exist other standards to add metadata to files : IPTC (Information Interchange Model),  XMP (Extensible Metadata Platform), … Both standards allow to embed informations about authors, locations, countries, subjects etc in the image files.

IPTC was developed in the early 1990s by the International Press Telecommunications Council (IPTC) to expedite the international exchange of news among newspapers and news agencies (IPTC Photo Metadata Standards : IPTC Core and IPTC Extension). The older IPTC metadata specification (IPTC-IIM) was frozen in 1997, and the IPTC organisation has been recommending the use of the XMP-based IPTC Core specifcation since 2004.

The ExifTool (current version 9.35 released on August 17, 2013) handles also IPTC and XMP metadata. A GUI (ExiftoolGUI : current version 5.15 released on January 8, 2013) for the ExifTool has been developed by Bogdan Hrastnik.

Another great utility allowing to read and write Exif, IPTC and XMP metadata is XnView, developed by Pierre Gougelet. This program handles more than 400 graphic file formats for import and more than 50 formats for export. A new project called XnViewMP (MP stands for multi platform) supports full multicode. Version 0.61 was released on July 18, 2013.

A C++ library and a command line utility to manage image metadata, called Exiv2, is available as free software and with a commercial license, and is used in many projects.The development of Exiv2 is lead by Andreas Huggel. Version Exiv2 0.23 was released on April, 2012.

Tags and other properties of a file can de added or modified in the Windows Explorer Detail Pane or in the Properties Pane.

The following list provides some useful guides about the right use of metadata in images and in other multimedia files :

Find images that contain a certain color

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Imagekind Artshop

The Multicolr Search Lab tool created by Idée Inc. allows to find images that share specified colours. There are others who offer this option.

Jim Bumgardner (alias krazydad) developed in 2006 a widget to search flickr photos by color (Colr Pickr). Color Hunter offers a similar service.

Google Image Search  lets you restrict the results based on color. For now, the option is not available in the user interface, but you can tweak the search results URL to try it. More informations are available at the Google Operating System Blog which is not affiliated with Google.

The Imagekind artshop lets you choose artworks by specifying a dominant and four other colors.

Etsy, an online shop of handmade products, has developed color search for their own product database.

PicItUp is a visual image search engine that combines word-based with color based search.

A COLOURlovers community, made up of people from around the world and from all walks of life, are gathering together under the common love of color.

Matt Mueller based the final project for his Computational Photography class on the Idée Labs tool Piximilar.

Daniel Flück posted his tool Color Name & Hue on his website colblindor. He was inspired by the tool Name that color created by Chirag Mehta.

A server version (isk-daemon) and a desktop version (imgSeek) of an image database management system have been developed by  Ricardo Niederberger Cabral as open-source project (licensed under the GPL). Color analysis is also a topic in the ImageMagick discussion forum.

Tilt-shift Photography : Miniature Fakes

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Tilt-Shift miniature faking is a creative technique whereby a photograph of a life-size location or object is manipulated to give an optical illusion of a photograph of a miniature scale model.

Altering the focus of the photography in Photoshop simulates the shallow depth of field normally encountered with macro lenses making the scene seem much smaller than it actually is.

In addition to focus manipulation, the tilt-shift photography effect is improved by increasing color saturation and contrast, to simulate the bright paint often found on scale models.

Most faked tilt-shift photographs are taken from a high angle to further simulate the effect of looking down on a miniature. The technique is particularly effective on buildings, cars, trains and people.

The following websites provide useful informations and tuotials about Tilt-Shift miniature faking :

Some outstanding tilt-shift photos published on flickr under a creative common licence are listed below:

There are currently 142 groups on flickr dealing with tilt-shift. My favorite pools are :

Tools to create photomosaics and tilemosaics

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Photomosaics are image montages which consist of small pictures called cell images. When viewed from a distance, you see the source image. Standard photo mosaic applications are based on similar processes. Applications are different in implemented recognition/selection algorithms and built-in functions for control/enhance mosaic rendering process.

The following tools are available :

The developer of Mosaic Creator published a comparison table of most available photo- and tile creation applications. A list of more tools is available in the Google directory.

Photo Mosaic

Photo Mosaic

Zoomify : zoomable web images

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Zoomify makes high-quality images zoom-and-pan for fast, interactive viewing on the web with just HTML, JPEGs, and Flash! Zoomify’s products meet the high-resolution imaging needs of creative professionals, image-centric businesses, and digital appliance companies. Zoomify is revolutionizing digital imaging in science, business, entertainment, education, and security.

Led by David Urbanic, President & CEO, Zoomify’s founders include top technologists and business staff from companies including Apple, Borland, Adobe and other leading firms.

There are four products available : Zoomify Express (free), Zoomify Design (29 US$), Zoomify Flash (129 US$) and Zoomify Enterprise (795 US$).

A detailed FAQ section is available at the website of Zoomify.

TinEye, PixID, Piximilar : advanced image software by Idée Inc.

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The canadian company Idée Inc. was founded by Leila Boujnane (CEO) and Paul Bloore (CTO). The company develops advanced image identification and visual search software.

PixID is an innovative video and still–image identification system that analyzes each client’s visual assets and actively tracks where their images have appeared, both in print publications and on the Internet. Idée’s proprietary software creates a digital fingerprint for each client image and compares it to images scanned from publications and crawled from the web.

Piximilar allows users to analyze, index and search quickly and efficiently through vast image and video collections based on visual similarity. Piximilar’s visual similarity technology uses sophisticated algorithms to analyze hundreds of image attributes such as colour, shape, texture, luminosity, complexity, objects and regions. These attributes form a unique visual signature.

With the Multicolr Search Lab, you can browse through 10 million of Flickr’s most ‘interesting’ Creative Commons images, and find ones that share the same colours. Choose up to 10 colours from our palette of 120 different shades.

TinEye is the first image search engine on the web to use image identification technology. Given an image to search for, TinEye tells you where and how that image appears all over the web—even if it has been modified. Just as you are familiar with entering text in a regular search engine such as Google to find web pages that contain that text, TinEye lets you submit an image to find web pages that contain that image. A beta version of TinEye is operationel.

TinEye Mobile allows you to search for products using your mobile phone’s camera.

The Idée Labs offer two other applications : Visual Search Lab and BYO Image Search Lab, both from the Alamy Stock Photos.

ImageMagick & PerlMagick

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ImageMagick® is a software suite to create, edit, and compose bitmap images. It can read, convert and write images in over 100 formats. ImageMagick can translate, flip, mirror, rotate, scale, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves.

ImageMagick is free software delivered as a ready-to-run binary distribution or as source code that you may freely use, copy, modify, and distribute. Its license is compatible with the GPL. It runs on all major operating systems and offers an iterface to most programming languages (Java, php, Perl, Pascal, Ruby, Python, C++, …).

The Definitive Guide to ImageMagick explains all of these capabilities and more in a practical, learn-by-example fashion, the book ImageMagick Tricks by Sohail Salehi is a fast-paced and practical tutorial packed with examples of photo manipulations, logo creation, animations, and complete web projects.

PerlMagick is an objected-oriented Perl interface to ImageMagick. This module can read, manipulate and write an image or image sequence from within a Perl script. This makes it very suitable for Web CGI scripts. I created the following test script on my hosted webserver to verify the correct configuration of ImageMagick and PerlMagick.

#!/usr/bin/perl -w
use strict;
use CGI::Carp qw(fatalsToBrowser);
use Image::Magick;
# created by Marco Barnig on 6th january 2009

my $headline = “Perl Test Script test9.pl”;

print “Content-type: text/htmlnn”;
print ‘<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN”>’, “n”;
print “<html><head><title>Perl Test</title></head><body>n”;
print “<h1>$headline</h1>n”;
print “<p>This test script opens an image file test.jpg, makes a clone, modify it and save it as mynew.gif</p>n”;

my $image1 = new Image::Magick;
my $status = $image1->Read( “../../httpdocs/media/test.jpg” );
die “Couldn’t open file test.jpg !” if “$status”;
my $image2 = $image1->Clone();
#blah, do something to $image2
$image2 -> Draw (
stroke    => “red”,
primitive => “line”,
points    => “20,20 180,180”);
my $status3 = $image2->Write( “gif:../../httpdocs/media/mynew.gif” );
die “Couldn’t save file mynew.gif in folder httpdocs/media !” if “$status3”;
print “<img src=”http://www.artgallery.lu/media/logo.gif”></img>n”;
print “<br/><br/>”;
print “<img src=”http://www.neen.lu/media/mynew.gif”></img>n”;
print “<br/><br/>”;
print “Das Script ist fertig”;
print “</body></html>n”;