eval alternative for non-sequental variable names

I want to apply a function to all instances of workspace variables that match a pattern, and overwrite those workspace variables with the function output. Currently I do this with a for loop and eval(). Is there a better way?

This case is similar to, but not quite equivalent to some of the cases described in http://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html?refresh=true.

I'd prefer a solution that does not require exchanging the workspace variable definitions for struct field definitions. I am unwilling to replace my variable names with sequential ones as I need meaningful names.

Example:

% 2D variables
i_red   = rand(10,20);
i_green = rand(10,20);
i_blue  = rand(10,20);

% function to evaluate
raster_scan = @(im) reshape(permute(im,[2 1]),[numel(im) 1]);

% for loop with eval
inputs=whos('i_*');
inputs={inputs.name};
for i=1:length(inputs)
    eval([inputs{i} '=raster_scan(' inputs{i} ');']);
end