artistic screening - mcgill university

Artistic ScreeningArtistic ScreeningV. Ostromoukhov, R.D. HerschV. Ostromoukhov, R.D. Hersch

Eric BlaisEric Blais

McGill C0S767 Winter 2004McGill C0S767 Winter 2004

OutlineOutline➔ Introduction/MotivationIntroduction/Motivation● HalftoningHalftoning● Artistic screeningArtistic screening● Summary/ConclusionsSummary/Conclusions


IntroductionIntroduction

Bella Vignette, by V. Ostromoukhov



Printing images in Printing images in black & white black & white introduces artifactsintroduces artifacts

Generally try to Generally try to avoid artifacts to avoid artifacts to reproduce the reproduce the original image as original image as faithfully as possiblefaithfully as possible

SmartCar, by C.Naylor



Artistic halftoning Artistic halftoning does not try to does not try to remove all artifactsremove all artifacts

Instead, control the Instead, control the artifacts to add artifacts to add another layer of another layer of information!information!

Detail of Bella Vignette, by V.Ostromoukhov


M.C. EscherM.C. Escher

Sky and Water Sky and Water woodcutwoodcut– Shows tiling of Shows tiling of

shapes... but also:shapes... but also:– Gradient of white to Gradient of white to

blackblack– The birds & the fish The birds & the fish

give the gradientgive the gradientSky and Water, by M.C. Escher


Islamic ArtIslamic Art

Alhambra (Spain)Alhambra (Spain)– From a distance: rich From a distance: rich

textures on all the wallstextures on all the walls– Up close: textures are Up close: textures are

created by finely-detailed created by finely-detailed tilestiles

Alhambra Detail, by Blair Fraser


OutlineOutline● Introduction/MotivationIntroduction/Motivation➔ HalftoningHalftoning● Artistic screeningArtistic screening● Summary/ConclusionsSummary/Conclusions


HalftoningHalftoning

Method of simulating gray levels using only Method of simulating gray levels using only black & whiteblack & white

Illusion of gray levels provided by individual Illusion of gray levels provided by individual shapes that “blend together” when seen shapes that “blend together” when seen from a distancefrom a distance


HalftoningHalftoning

Three methods:Three methods:– TraditionalTraditional

““Newspaper”-style halftoningNewspaper”-style halftoning

– Threshold Threshold Sometimes known as ditheringSometimes known as dithering

– PatternPattern Will be used for artistic halftoningWill be used for artistic halftoning


Traditional HalftoningTraditional Halftoning

Gray levels created Gray levels created by dots of different by dots of different sizessizes

Best for printers Best for printers with low resolution with low resolution but variable dot sizebut variable dot size

Can be seen by looking closely at Can be seen by looking closely at newspaper imagesnewspaper images



First Step: divide the input image into First Step: divide the input image into tilestiles Individual tiles are called Individual tiles are called screen elementsscreen elements

– In this example, each In this example, each grid square (about grid square (about 16x16 pixels) 16x16 pixels) corresponds to one corresponds to one screen elementscreen element



Second step: add Second step: add one dot per screen one dot per screen elementelement

Size of the dot Size of the dot determined by the determined by the average colour of average colour of the screen elementthe screen element



Edges are not really Edges are not really sharpsharp

Can improve results Can improve results with diagonal grids, with diagonal grids, non-circular dotsnon-circular dots

Quality of results depends heavily on the Quality of results depends heavily on the output resolutionoutput resolution


Threshold HalftoningThreshold Halftoning

Alternative to the Alternative to the traditional methodtraditional method

No colour averaging No colour averaging within the screen within the screen elementselements

Gives a more Gives a more accurate pictureaccurate picture



First Step: divide the image into screen First Step: divide the image into screen elementselements– Same as beforeSame as before



Second step: define a threshold for each Second step: define a threshold for each pixel in the screen elementpixel in the screen element

Only pixels darker than their associated Only pixels darker than their associated threshold are drawn in the output imagethreshold are drawn in the output image

V.O. & R.D.H.



Creates sharper edges Creates sharper edges than traditional methodthan traditional method

Dots are not always Dots are not always complete!complete!


Pattern HalftoningPattern Halftoning

Gets rid of the Gets rid of the threshold functionthreshold function

Instead, uses Instead, uses pattern images to pattern images to create illusion of create illusion of gray levelsgray levels

Much more flexible!Much more flexible!

Warrior, by V. Ostromoukhov



Additional pre-processing step Additional pre-processing step is required:is required:

Create a screen element Create a screen element pattern for each gray levelpattern for each gray level– Any pattern is possible, as long Any pattern is possible, as long

as similar gray levels have similar as similar gray levels have similar pattern imagespattern images

V.O. & R.D.H.



Next step:Next step:– Once again, divide Once again, divide

the image into the image into screen elementsscreen elements



Last step: use the patterns to form the Last step: use the patterns to form the final imagefinal image

A pixel's colour determines which pattern A pixel's colour determines which pattern image is sampled at that positionimage is sampled at that position



Results can be much more interesting than Results can be much more interesting than traditional or threshold halftoning methods!traditional or threshold halftoning methods!

If pattern images are stored in a library, If pattern images are stored in a library, this method is about as fast as the other this method is about as fast as the other two methodstwo methods

V.O. & R.D.H.


OutlineOutline● Introduction/MotivationIntroduction/Motivation● HalftoningHalftoning➔ Artistic ScreeningArtistic Screening● Summary/ConclusionsSummary/Conclusions


Artistic ScreeningArtistic Screening

Creation of artistic pattern imagesCreation of artistic pattern images Edges smoothingEdges smoothing Multiple patternsMultiple patterns Screen distortionsScreen distortions


Creating pattern imagesCreating pattern images

Creating the pattern image for each gray Creating the pattern image for each gray level by hand is possible...level by hand is possible...– TediousTedious– Very time consumingVery time consuming– Difficult to change the number of gray levels Difficult to change the number of gray levels

afterwardsafterwards– Cannot adjust the screen element shape or size Cannot adjust the screen element shape or size

afterwardsafterwards


Creating pattern shapesCreating pattern shapes

There is a better way:There is a better way:– The artist defines the contour of the pattern The artist defines the contour of the pattern

for specific gray levels for specific gray levels – Can be done in any commercial shape Can be done in any commercial shape

drawing applicationdrawing application

V.O. & R.D.H.


Interpolating pattern shapesInterpolating pattern shapes

Shape blending Shape blending algorithm used to algorithm used to interpolate between interpolate between the defined contours the defined contours

Can blend between any Can blend between any number of gray levelsnumber of gray levels

V.O. & R.D.H.


Creating pattern imagesCreating pattern images

DiscretizationDiscretization– Pattern images are Pattern images are

created from the created from the contours for each contours for each gray levelgray level

V.O. & R.D.H.


Creating patterns - reviewCreating patterns - review

V.O. & R.D.H.


Edge SmoothingEdge Smoothing

Problem:Problem:– Sharp edges cause Sharp edges cause

discontinuities in our discontinuities in our patternspatterns

V.O. & R.D.H.


Edge SmoothingEdge Smoothing

Solution is simpleSolution is simple– Simply blur the Simply blur the

original imageoriginal image– Lose the sharpness Lose the sharpness

of edges, but now of edges, but now the patterns are the patterns are continuouscontinuous

V.O. & R.D.H.


Multiple PatternsMultiple Patterns

Can also use multiple patterns on the same Can also use multiple patterns on the same imageimage

V.O. & R.D.H.


Multiple PatternsMultiple Patterns

Detail of the Ibn Tulun Mosque, by R.&S. Michaud


Screen DistortionScreen Distortion

So far, we have applied the patterns to So far, we have applied the patterns to the image in a simple grid patternthe image in a simple grid pattern



Can also use a non-linear mapping Can also use a non-linear mapping between the screen elements and the between the screen elements and the pattern shapespattern shapes



Original image is unchanged – only the Original image is unchanged – only the pattern shapes are distoredpattern shapes are distored

V.O. & R.D.H.


OutlineOutline● Introduction/MotivationIntroduction/Motivation● HalftoningHalftoning● Artistic ScreeningArtistic Screening➔ Summary/ConclusionsSummary/Conclusions


SummarySummary

Artistic Screening is a new halftoning Artistic Screening is a new halftoning technique that lets designers freely create technique that lets designers freely create custom halftone pattern shapescustom halftone pattern shapes

New types of images possible with 2 layers New types of images possible with 2 layers of information of information


ConclusionsConclusions

Interesting techniqueInteresting technique Some of the places where it can be useful:Some of the places where it can be useful:

– Event postersEvent posters– BillboardsBillboards– Improved security features for banknotesImproved security features for banknotes


Kabuki event posterKabuki event poster

Kabuki actor, by Toshusai Sharaku


Jeremias Gotthelf billboardJeremias Gotthelf billboard

Gotthelf portrait, V. Ostromoukhov


Safety features for banknotesSafety features for banknotes

V.O. & R.D.H.

artistic screening - mcgill university

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