Logarithmic Image Processing Logarithmic Image Processing (LIP)(LIP)

ByBy

Ben WeisenbeckBen Weisenbeck

Oiki WongOiki Wong

IntroductioIntroductionn

Q: Why LIP?Q: Why LIP?A: Contrast Stretching and Image Sharpening A: Contrast Stretching and Image Sharpening

simultaneouslysimultaneously

Q: Why not histogram equalization?Q: Why not histogram equalization?A: A flat histogram often times are not what is A: A flat histogram often times are not what is

needed to enhance certain features within needed to enhance certain features within the image. the image.

Image Enhanced),( jif

n)(n x size ow with windImage Averaged),( jia

))],(log()),([log()),(log()),(log( jiajifjiajif

Image Orignal),( jif

Key Things

α governs the contrast of the image

β governs the sharpness of the image

Main IdeaMain Idea

Tune the parameters until you get what you want. But first, know what each parameter does!

•α governs the contrast of the image:•α >1 Brings out bright areas•α <1 Brings out dark areas•α < 0 Negative Transformation

•β governs the sharpness of the image:•β >1 Sharpening•β <1 Blurring

•n x n window also governs the sharpness of the image•Bigger is not always better

Examples of Histogram Equalization isn’t the answerExamples of Histogram Equalization isn’t the answer

Examples of Histogram Equalization isn’t the answerExamples of Histogram Equalization isn’t the answer

Graphical User InterfaceGraphical User Interface

Graphical User InterfaceGraphical User Interface

Enhancing Dark DetailsEnhancing Dark Details

Enhancing Dark DetailsEnhancing Dark Details

Enhancing Dark DetailsEnhancing Dark Details

Enhancing Bright DetailsEnhancing Bright Details

Color EnrichmentColor Enrichment

Our result shows that the algorithm can also create color enrichment to a certain degree. This is something that histogram equalization fails to perform.

The color in the words “U.S AIR FORCE” stands out much more in the enhanced image. Also note that the shadow in the mountain is “deeper” than the original.

Color EnrichmentColor Enrichment

Histogram Equalization creates an illusion that the flight was in bad weather!

Window SizingWindow Sizing

LIP with 3x3 window LIP with 9x9 window

NoiseNoise

F(ij)=B(i,j)+noise

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1),(

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jiB

noise

jiB

jiF

SummarySummary

ParametersParameters αα controls the contrast controls the contrast enhancement ββ controls the sharpness of the controls the sharpness of the

image.image. Larger Window size => sharper edgesLarger Window size => sharper edges

Superior to Histogram EqualizationSuperior to Histogram Equalization Black and White imagesBlack and White images Color imagesColor images Noisy ImagesNoisy Images

ConclusionConclusion

AdvantagesAdvantages Simultaneous enhancement of contrast Simultaneous enhancement of contrast

and sharpnessand sharpness Fine-tuned control over image Fine-tuned control over image

enhancementenhancement DisadvantageDisadvantage

Parameter values must be carefully Parameter values must be carefully selected and adjusted to obtain desirable selected and adjusted to obtain desirable resultsresults

Questions?Questions?