Unity Web Request texture downloading takes too much memory

Hello,

Background
I'm currently trying to optimize the memory consumption of an app. We need to download a lot of images.

Problem:
1) Try downloading an image (try with png or jpg). I'm currently testing with a 1.4mb image.
2) After download, the memory went from 20.6 to 26.1mb. Which means that it is taking 5.5mb instead of 1.4mb.

Could anyone help or provide more insight?
Thank you in advance.

 

Image size on disk is not the same size in memory. This is due to decompression. png / jpg are compressions made for your disk. Whenever you use UWR to download a texture it will decompress it as RGB24 (jpg) or RGB32 (png). Which is an uncompressed large texture, hence your memory usage increasing.

Whenever you add png's / jpgs to the Editor, Unity converts them to a format that the GPU can use. Such as DXT, ETC2, PVRTC and some others. These have a smaller memory footprint.

 

What would be a good workaround for this issue? What you are saying makes sense, do you have some link where I could get more info?

 

One option is to store the PNG file locally as an array of bytes, writing it to the local filesystem.

When you need to show some images, pull them up and "realize" them into Texture2Ds.

For extra credit you could resize the images into small previews that you show before you load and unpack the real ones.

 

I believe that I do that already, since I am saving them in the cache. Then I take them after encoding them and lowering their quality.

 

@marcolbx did you find a solution?

 

As said previously, loading png (avoid the lossy jpg format) files will result in uncompressed textures that will use a lot of memory.

To avoid that, either :
- Convert your textures beforehand in the appropriate format depending on the target platform (DXT for desktop, ETC/EAC for mobile). The caveat is that this will increase significantly the size of the file compared to png compression, making the download larger/slower, which might or might not be an issue in practice depending on your use case.
- Keep downloading png files, but compress them on the fly (see Texture2D.Compress()). Caveat is that this add some processing time, and compression quality will be lower.

Also make sure that you make textures non readable (see the docs), as on most platforms this will cause an additional copy of the texture to be stored in memory.

 

Right, using Compress is probably the best option. Though note that if the texture has read / write enabled, you would still have an uncompressed version on the CPU side in your main memory. Compessing to DXT only helps with GPU memory. You can mark a texture as no longer being readable by calling Apply on the texture and set the "makeNoLongerReadable" parameter to true.

Of course once you did this you can no longer access the texture data on the CPU. So GetPixels would not work anymore as the texture would now only live in GPU memory. So this approach is probably the best when you just want to load ordinary textures externally as you usually do not need to modify them. Of course there are ways to extract texture data from the GPU memory, but it's slow. You have to create a rendertexture, use Graphics.Blit to copy the content on the GPU into the rendertexture and use ReadPixels with the render texture active to read the content into another new Texture2d. There may be other ways now since we have more lowlevel access now to textures. Though in general "downloading" texture data from the GPU to the CPU is generally quite heavy.