Generate Ishihara-Style Color Vision Test Plates

Convert a source image into an Ishihara-style dot plate by using a binary mask to assign foreground and background dot colors

Ishihara plates encode a numeral or shape using colored dots so that the figure is distinguished primarily by chromatic contrast. This example constructs an Ishihara-style visualization from a source image by converting it to a binary mask and using that mask to color a field of randomly sampled disks. The result is inspired by traditional Ishihara plates and is not intended as a clinical diagnostic test.

Create a high-contrast source image containing a bold numeral on a lightly textured background:

In[1]:=

sourceImage=BlockRandom[SeedRandom[12];Rasterize[Graphics[Join[{RGBColor[0.96,0.96,0.90],Rectangle[{0,0},{500,500}]},Table[{Opacity[0.25],GrayLevel[RandomReal[{0.75,0.9}]],Disk[RandomReal[{0,500},2],RandomReal[{2,5}]]},{700}],{Black,Text[Style["5",360,Bold,FontFamily"Helvetica"],{250,245}]}],PlotRange{{0,500},{0,500}},ImageSize500,BackgroundWhite],"Image",RasterSize{500,500}]]

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Define a helper function that converts the source image into a filled binary mask. This mask identifies the region that will receive the foreground dot colors in the final plate:

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buildIshiharaMask[img_Image,size_,threshold_,shapeDilation_]:=Module[{gray},gray=ColorConvert[ImageCrop[ImageResize[img,size],{size,size}],"Grayscale"];Dilation[FillingTransform[DeleteSmallComponents[ColorNegate[Binarize[gray,threshold]],100]],DiskMatrix[shapeDilation]]]

Apply the mask construction step separately to verify that the numeral is clearly isolated before generating the dot plate:

In[3]:=

mask=buildIshiharaMask[sourceImage,500,0.55,2]

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Define the default parameters that control the size of the plate, the number and size of the dots, the mask construction, and the foreground and background color palettes:

In[4]:=

Options[ishiharaStylePlate]={"ImageSize"500,"DotCount"12000,"DotRadiusRange"{1.2,2.8},"Threshold"0.55,"ShapeDilation"2,"ForegroundPalette"{RGBColor[0.79,0.43,0.32],RGBColor[0.84,0.49,0.36],RGBColor[0.72,0.38,0.30],RGBColor[0.88,0.55,0.40]},"BackgroundPalette"{RGBColor[0.46,0.68,0.36],RGBColor[0.54,0.74,0.42],RGBColor[0.40,0.62,0.32],RGBColor[0.60,0.78,0.48]},"RandomSeed"23};

Define the function that samples random dot positions inside a circular region and colors each dot according to whether it falls inside or outside the source mask:

In[5]:=

ishiharaStylePlate[img_Image,opts:OptionsPattern[]]:=Module[{size,dotCount,radiusRange,threshold,shapeDilation,foregroundPalette,backgroundPalette,seed,mask,maskData,width,height,points,pixelPositions,maskValues,radii,colors,graphic},size=OptionValue["ImageSize"];dotCount=OptionValue["DotCount"];radiusRange=OptionValue["DotRadiusRange"];threshold=OptionValue["Threshold"];shapeDilation=OptionValue["ShapeDilation"];foregroundPalette=OptionValue["ForegroundPalette"];backgroundPalette=OptionValue["BackgroundPalette"];seed=OptionValue["RandomSeed"];mask=buildIshiharaMask[img,size,threshold,shapeDilation];maskData=ImageData[mask,"Bit"];{width,height}=ImageDimensions[mask];BlockRandom[SeedRandom[seed];points=RandomPoint[Disk[{width/2,height/2},0.48Min[{width,height}]],dotCount];pixelPositions=({Clip[height-Round[#〚2〛]+1,{1,height}],Clip[Round[#〚1〛],{1,width}]}&)/@points;maskValues=Extract[maskData,pixelPositions];radii=RandomReal[radiusRange,dotCount];colors=(If[#1,RandomChoice[foregroundPalette],RandomChoice[backgroundPalette]]&)/@maskValues;graphic=Graphics[MapThread[{#3,Disk[#1,#2]}&,{points,radii,colors}],PlotRange{{0,width},{0,height}},BackgroundWhite,ImageSizesize];Rasterize[graphic,"Image",RasterSize{size,size}]]]

Apply the plate generator to the source image to create the final dotted visualization:

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plate=ishiharaStylePlate[sourceImage]

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External Links

https://community.wolfram.com/groups/-/m/t/2963560

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Citation:
- Based on Aishwarya Main’s Wolfram Community post, “[WSRP23] Function that turns any image into an Ishihara's test for color deficiency.”

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Contributed by: Wolfram Staff

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Generate Ishihara-Style Color Vision Test Plates

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