How to render a UE asset thumbnail in a non-UE application

Development Programming & Scripting C++
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1

Using the UnrealEd module I can successfully get a uasset thumbnail as a TArray with a call to FObjectThumbnail::AccessCompressedImageData(). I can then transfer this byte array to a different non-UE application where I can realize the image. The problem is the image colors are incorrect. I have tried many different approaches to realizing the image in the second application (C#, Java), but nothing seems to work. I have attached screen shots of both the good image and the bad. Any help would be greatly appreciated.

230721-correct-colors.png

230722-wrong-colors.png

The image with the blue sky is the correct and desired image.

2

When you make byte array swap red value with blue value, you maybe setting bytes in incorrect RGB order or your C# program read them in incorrect order, since you can clearly see on the image that red is blue and blue is red

3

Thank you your answer is a good one! While I do not understand where or why the red and blue colors are being flipped in the process, if I swap the red with the blue in my receiving application then the image appears correct once again. Thanks again!

4

Hey do you mind explanning how did you convert the image into a file?
I am trying to figure it out for ages,
I tried using FFileHelper::CreateBitmap and FFileHelper::SaveArrayToFile
Thanks in advance :slight_smile:

5

I got the following from a colleague. I have not used it myself, but it comes from a reliable source.
I hope it will help you.

This method will save a UTexture2D as a PNG in the content directory as “MyImage.png”. If you go into HighResScreenshotConfig.SaveImage you can see its using FImageWriter and FArchive to get the job done.

void SaveTexture2D(UTexture2D* PTexture) {
PTexture->UpdateResource();
FTexture2DMipMap* MM = &PTexture->PlatformData->Mips[0];

TArray<FColor> OutBMP;
int sz = MM->SizeX * MM->SizeY;
OutBMP.AddUninitialized(sz);
FColor* FormatedImageData = static_cast<FColor*>(MM->BulkData.Lock(LOCK_READ_ONLY));
FMemory::Memcpy(OutBMP.GetData(), FormatedImageData, sz * sizeof(FColor));
MM->BulkData.Unlock();

// SaveImage knows how to save the bitmap as PNG - saves to disk file
FHighResScreenshotConfig& HighResScreenshotConfig = GetHighResScreenshotConfig();
HighResScreenshotConfig.SetHDRCapture(false);
FString filename = FPaths::Combine(*FPaths::ProjectContentDir(), TEXT("MyImage.png"));
bool bSaved = HighResScreenshotConfig.SaveImage(filename, OutBMP, FIntPoint(MM->SizeX, MM->SizeY));
}