large memory consumption and low quality

[jdevp]

Hi, it's a good job to start with. However, I see the following issues.

1. Low quality image captured if given ratio 1. If I scale the image based on device pixel ratio, the image becomes very large to save. It quickly uses up a lot of memory if I use 'png' format which causes app crashes. It seems to work fine with 'rawrgba' format but the size is very large.
2. The method 'toImageSync' app crashes due to memory usage as well. It works with by using 'toImage'.

I don't know if there is a way to solve those issues by using isolates.