Memory size is greater than image sizes? how to free memory on navigating back?

I am displaying 300+ items in a listview and each having image defined as below. Images are retrieved from aws s3 bucket. I profiled memory usage with xamarin profiler and I can see that the more I scroll in the list, memory usage increases which makes sense as each images are cached. But I am going above 300 mb cache. total size of all images physically are not more than 15 mb.

1. How can it be cached 20 times more than actual size? If I use loading.png for loadingplaceholder, is it also cached for 300 times for each item in the list?

2. When i navigate back from the list, my memory size is not reduced. this is probably expected as some people may want to keep them in memory. Is there an option free the memory in build? a parameter or something?

<ffimageloading:CachedImage  RetryCount="1"	
DownsampleToViewSize="true" 
 TransparencyEnabled = "false"  CacheDuration = "30" 
LoadingPlaceholder="loading_dark.png"    ErrorPlaceholder="error.png"   
Source="{Binding Image, Converter={StaticResource thumbnailConvertor}}"
  Aspect="AspectFit"    />

[daniel-luberda]

As @molinch said:

downloaded file size != bitmap size in memory

1px = 4 Bytes (Android ARGB_8888) 
1024px x 1024px = 4 Megabytes
 2048px x 2048px = 16 Megabytes

Every PNG / JPG is decoded into a bitmap, there’s no other way. That’s why downscaling is so important.

[daniel-luberda]

@EmilAlipiev

You can control memory cache size by yourself 😃 Just use custom FFImageLoading config:

var config = new FFImageLoading.Config.Configuration()
{
    MaxMemoryCacheSize = 9999999,
};
ImageService.Instance.Initialize(config);