Calculating Ratio of black to white pixels in camera output

Development Rendering
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1

Hi. I’m trying to calculate the ratio 0-1 of black and white pixels in a material. I need this value to calculate a drag function to try and simulate aerodynamics. Unfortunately I can’t seem to find any information on how exactly I’d get that data and for the life of me I’m stumped.
Example image of what I’m working with attatched.
Capturar

2

.h

will need include
#include “Structs.h”

ratio struct



USTRUCT(BlueprintType)
struct FRatios
{
	GENERATED_BODY();
public:
	UPROPERTY(BlueprintReadOnly, VisibleAnywhere, Transient, meta = (NoSpinbox = true))
		int32 color1Ratio;

	UPROPERTY(BlueprintReadOnly, VisibleAnywhere, Transient, meta = (NoSpinbox = true))
		int32 color2Ratio;
};

		UFUNCTION(BlueprintCallable)
			static FRatios CalulateColorRatio(UTexture2D* PassedAsset, FColor Color1, FColor Color2);

Static function implementation in blueprintlibrary

FRatios UImageFunctionLibrary::CalulateColorRatio(UTexture2D* PassedAsset, FColor Color1, FColor Color2) {

	int32 sizeX = PassedAsset->GetSizeX();
	int32 sizeY = PassedAsset->GetSizeY();

	FRatios ret;
	ret.color1Ratio = 0;
	ret.color2Ratio = 0;

	int32 Color1Amount = 0;
	int32 Color2Amount = 0;

	if (PassedAsset != nullptr) {
		TextureCompressionSettings OldCompressionSettings = PassedAsset->CompressionSettings; TextureMipGenSettings OldMipGenSettings = PassedAsset->MipGenSettings; bool OldSRGB = PassedAsset->SRGB;

		PassedAsset->CompressionSettings = TextureCompressionSettings::TC_VectorDisplacementmap;
		PassedAsset->MipGenSettings = TextureMipGenSettings::TMGS_NoMipmaps;
		PassedAsset->SRGB = false;
		PassedAsset->UpdateResource();

		const FColor* FormatedImageData = reinterpret_cast<const FColor*>(PassedAsset->PlatformData->Mips[0].BulkData.LockReadOnly());

		for (int32 X = 0; X < sizeX; X++)
		{
			for (int32 Y = 0; Y < sizeY; Y++)
			{
				FColor PixelColor = FormatedImageData[Y * sizeX + X];
				if (PixelColor == Color1) {
					Color1Amount++;
				}
				else if (PixelColor == Color2) {
					Color2Amount++;
				}
			}
		}
		PassedAsset->PlatformData->Mips[0].BulkData.Unlock();
		PassedAsset->CompressionSettings = OldCompressionSettings;
		PassedAsset->MipGenSettings = OldMipGenSettings;
		PassedAsset->SRGB = OldSRGB;
		PassedAsset->UpdateResource();


		int32 commonDiv = FMath::GreatestCommonDivisor(Color1Amount, Color2Amount);
	
		if (commonDiv != 0) {
			ret.color1Ratio = Color1Amount / commonDiv;
			ret.color2Ratio = Color2Amount / commonDiv;
			return ret;
		}		
	}
	return ret;
}

When passing in colors make sure the alpha is set to 1 otherwise the comparison will fail

OFC passed in 2 colors will be black and white color variables.

Pixel code reading sourced from

I didn’t put a strict division of the returned ratio x : y seeing it’s probably easier to just manipulate the returned values as needed.

3

Thanks, I found a blueprints based solution but it’s horrifically un-performant. I’ll have to get on this later to patch things up.