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Accessing pixel values of Texture2D

I was wondering if there is a way to read/write pixel values on a UTexture2D object (e.g. read values from a heightmap or draw something on a texture).

I've seen that there are FTexture2DMipMaps stored on the Texture that contain BulkData, which might be the pixel data of the texture. My idea was to get the first mip map and access its data somehow.

Is this even possible? Maybe somebody could give me some pointers in which direction to go.

Thanks!

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asked Apr 06 '14 at 08:38 PM in C++ Programming

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TaurusI76
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1 answer: sort voted first

First you need to understand that a texture is normally, a sum of multiple images called MipMaps. MipMaps are down-scaled versions of your images, always in steps of power of 2, so the original image, is, say, 512x512 - this would be the MipMap "0", then the engine generates the MipMap "1" which is 256x256 and then MipMap "2" which is 128x128, this continues on down to 16x16 I think. The farther away the texture is rendered, the smaller version of the image is used. This means that you need to access the mipmap 0 of your texture.


First we need to access the mipmap 0 of the texture, it is important to only access the data we need through refrences or, like I did here, pointers, either will do. We do this to directly access the original data in the memory instead of copying that data into a local variable. This saves memory and speed:

 FTexture2DMipMap* MyMipMap = &MyTexture2D->PlatformData->Mips[0];

With this, we can access the BulkData which contains the raw image data:

 FByteBulkData* RawImageData = &MyMipMap->BulkData;

Considering this texture data is used in the rendering thread, we need to lock it to make sure nothing else can access it while we are using it, if we didn't, we could cause memory corruptions or crashes. So now we lock the image data which will also return a pointer to it - which we can then go ahead and cast the unformated data into an array of FColor's:

 FColor* FormatedImageData = static_cast<FColor*>( RawImageData->Lock( LOCK_READ_ONLY ) );

The FColor array is ofc 1 dimensional. So to access certain parts of the image, we need to use the width and height of the texture to calculate the position of the pixel we are wanting to lookup. Here's a small statement that does just that:

 uint8 PixelX = 5, PixelY = 10;
 uint32 TextureWidth = MyMipMap->SizeX, TextureHeight = MyMipMap->SizeY;
 FColor PixelColor;
 
 if( PixelX >= 0 && PixelX < TextureWidth && PixelY >= 0 && PixelY < TextureHeight )
 {
     PixelColor = FormatedImageData[ PixelY * TextureWidth + PixelX ];
 }

Now, for demonstration purposes, I broke down each step. We could easily access and cast this in one line:

 FColor* FormatedImageData = static_cast<FColor*>( MyTexture2D->PlatformData->Mips[0].BulkData.Lock( LOCK_READ_ONLY ) );

And now that we are done with everything, we need to unlock the memory again:

 RawImageData->Unlock();

or

 MyTexture2D->PlatformData->Mips[0].BulkData.Unlock();


Hope this helps.

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answered Jul 23 '14 at 07:16 AM

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xC0DEB10C
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avatar image Grogger Jan 22 '15 at 04:35 PM

I've tried this without success. A completely black image (32x32 DXT1) is returning values like:

 (R=0,G=0,B=0,A=0)
 (R=170,G=170,B=170,A=170)
 (R=0,G=0,B=0,A=0)
 (R=170,G=170,B=170,A=170)
 etc...

Does the mip map raw data already account for texture pitch?

Edit: I just realized this post was old, hopefully you (or anyone) is still around to answer the question though.

avatar image TalkingGoose Jan 28 '15 at 07:05 PM

The given solution seems to work fine if the following settings are used for the texture;

  • Mip Gen Settings: NoMipmaps

  • sRGB: false

  • Compression Settings: TC Vector Displacementmap

This article might also be of use.

avatar image Robo Platypus Feb 22 '17 at 08:39 PM

On the off chance anybody reads this: TC Vector won't appear in your editor if you set the texture group to UI. Instead do-

Compression Settings: UserInterface2D (RGBA)

avatar image Stratego99 Mar 12 '17 at 09:59 PM

Thank you so much, the answer I needed in the smallest of corners.

avatar image renel degazon Nov 11 '17 at 08:26 PM

How would you go about getting the center of those pixels?

avatar image PowerDesign Feb 17 '16 at 06:03 AM

It works for me. Is it possible to sample the texture with bilinear filter? I don't want the exact pixel value, I need the interpolated value.

Does locking/unlocking frequently affects performance?

Thanks!

avatar image BálintYYY May 13 '16 at 05:08 PM

Can you answer this question in bluepprints, Thanks!

avatar image Ragethunder Jul 30 '16 at 12:55 PM

Hey guys! I've done the exact same thing and my editor keeps crashing when I hit play. What I did was make a public Texture2D reference variable in my blueprint class created from my c++ class, asigned a image with NoMipmaps, sRGB: false and VectorDisplacementmap (RGBA8). I've then called this code via ReadPixel function I've exposed to ue4, but it crashes. What I've managed to do is locate that PlatformData->Mips[0] crashes the editor for some reason. Any ideas?

avatar image MaxPower42 Aug 05 '16 at 05:45 PM

Hi. I used this code to read layer-info from landscape weight map textures.

But what if I want to modify the texture? I changed the lock mode to read/write and wrote colors to the pixel-array, but I didn't see any effect afterwards :(

avatar image MaxPower42 Sep 06 '16 at 11:50 PM

Help please!!

I was able to dynamically change textures by procedurally editing their bulk-data, but the next time I restart my project/editor all the changes are reverted.

So how do I save the modified bulkdata to disk? I saved the texture asset after modifying it, but that's not enough.

edit: actually, nevermind. I found the "persistent" data under UTexture2D::Source.

avatar image Teapot Creation Sep 29 '16 at 02:55 PM

Hi, any idea about how to do this using blueprints ?

avatar image pemcode Oct 13 '16 at 06:35 AM

What about on Android? I set texture settings to VectorDisplacementmap (RGBA8) and it works on WIndows desktop. However, it doesn't work on Android. I think maybe that's because UE4 on Android uses a different texture format maybe?

avatar image invrsion Mar 16 '17 at 01:51 PM

I've tried your method but my result is always the same color (205, 205, 205) for each pixel, that doesn't match the visual content of the same texture applied to some mesh in game, have you any ideas?

Thanks.

avatar image resul4e Mar 21 '17 at 11:46 AM

I've got the same issue as invrsion. Does anybody know how to fix this? Or did you fix it invrsion?

avatar image RubiousOctopus Dec 07 '17 at 09:00 PM

Same issue here, I can't UpdateTextureRegions also :(

avatar image Two-faced Mar 23 '17 at 12:36 PM

Such a hot topic!

I'm trying to find a BP solution too, so there is a Image (Texture2D) to Bytes (PNG) node from Low Entry Extended Standart Library.

avatar image Two-faced Mar 24 '17 at 12:57 PM

And here is the answer: Victory Plugin.

avatar image Defthorizon Mar 19 '18 at 10:51 PM

If it's crashing for you, try changing 'FByteBulkData' to 'FUntypedBulkData'. It worked for me!

Hope this helped someone!

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