5 added 1 character in body

MATL, 36 29 bytes

5l$rtP+!kllII$r*O16tQ/XE'a'YG


This saves the result in file a.png.

Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file:

5l$rtP+!kllII$r*O16tQ/XE2YG


Here's an example output: Explanation

5l$r % 5×5 matrix of independent random values with uniform distribution % on the interval (0,1) tP+! % Duplicate, flip vertically, add, transpose. This gives a horizontally % symetric matrix. Center column pixels are uniformly distributed on the % interval (0,2). Rest have a triangular distribution on (0,2) k % Round down. In either of the above cases, this gives 0 and 1 % with the same probability llII$r   % 1×1×3 array of independent random numbers with uniform distribution
% on (0,1). This is the foreground color.
*        % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the
% 5×5 array become the random foreground color. Zeros remain as zeros.
O        % Push 0
16tQ/    % 16, duplicate, add 1, divide: gives 16/17, or 240/155255
XE       % Replace 0 by 16/17: background color
'a'      % Push file name
YG       % Write image to that file


MATL, 36 29 bytes

5l$rtP+!kllII$r*O16tQ/XE'a'YG


This saves the result in file a.png.

Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file:

5l$rtP+!kllII$r*O16tQ/XE2YG


Here's an example output: Explanation

5l$r % 5×5 matrix of independent random values with uniform distribution % on the interval (0,1) tP+! % Duplicate, flip vertically, add, transpose. This gives a horizontally % symetric matrix. Center column pixels are uniformly distributed on the % interval (0,2). Rest have a triangular distribution on (0,2) k % Round down. In either of the above cases, this gives 0 and 1 % with the same probability llII$r   % 1×1×3 array of independent random numbers with uniform distribution
% on (0,1). This is the foreground color.
*        % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the
% 5×5 array become the random foreground color. Zeros remain as zeros.
O        % Push 0
16tQ/    % 16, duplicate, add 1, divide: gives 16/17, or 240/155
XE       % Replace 0 by 16/17: background color
'a'      % Push file name
YG       % Write image to that file


MATL, 36 29 bytes

5l$rtP+!kllII$r*O16tQ/XE'a'YG


This saves the result in file a.png.

Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file:

5l$rtP+!kllII$r*O16tQ/XE2YG


Here's an example output: Explanation

5l$r % 5×5 matrix of independent random values with uniform distribution % on the interval (0,1) tP+! % Duplicate, flip vertically, add, transpose. This gives a horizontally % symetric matrix. Center column pixels are uniformly distributed on the % interval (0,2). Rest have a triangular distribution on (0,2) k % Round down. In either of the above cases, this gives 0 and 1 % with the same probability llII$r   % 1×1×3 array of independent random numbers with uniform distribution
% on (0,1). This is the foreground color.
*        % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the
% 5×5 array become the random foreground color. Zeros remain as zeros.
O        % Push 0
16tQ/    % 16, duplicate, add 1, divide: gives 16/17, or 240/255
XE       % Replace 0 by 16/17: background color
'a'      % Push file name
YG       % Write image to that file

4 added 5 characters in body

MATL, 36 29 bytes

5l$rtP+!kllII$r*O16tQ/XE'a'YG


This saves the result in file a.png.

Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file:

5l$rtP+!kllII$r*O16tQ/XE2YG


Here's an example output: Explanation

5l$r % 5×5 matrix of independent random values with uniform distribution % on the interval (0,1) tP+! % Duplicate, flip vertically, add, transpose. This gives a verticallyhorizontally % symetric matrix. Center rowcolumn pixels are uniformly distributed on the % interval (0,2). Rest have a triangular distribution on (0,2) k % Round down. In either of the above cases, this gives 0 and 1 % with the same probability llII$r   % 1×1×3 array of independent random numbers with uniform distribution
% on (0,1). This is the foreground color.
*        % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the
% 5×5 array become the random foreground color. Zeros remain as zeros.
O        % Push 0
16tQ/    % 16, duplicate, add 1, divide: gives 16/17, or 240/155
XE       % Replace 0 by 16/17: background color
'a'      % Push file name
YG       % Write image to that file


MATL, 36 29 bytes

5l$rtP+!kllII$r*O16tQ/XE'a'YG


This saves the result in file a.png.

Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file:

5l$rtP+!kllII$r*O16tQ/XE2YG


Here's an example output: Explanation

5l$r % 5×5 matrix of independent random values with uniform distribution % on the interval (0,1) tP+! % Duplicate, flip vertically, add, transpose. This gives a vertically % symetric matrix. Center row pixels are uniformly distributed on the % interval (0,2). Rest have a triangular distribution on (0,2) k % Round down. In either of the above cases, this gives 0 and 1 % with the same probability llII$r   % 1×1×3 array of independent random numbers with uniform distribution
% on (0,1). This is the foreground color.
*        % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the
% 5×5 array become the random foreground color. Zeros remain as zeros.
O        % Push 0
16tQ/    % 16, duplicate, add 1, divide: gives 16/17, or 240/155
XE       % Replace 0 by 16/17: background color
'a'      % Push file name
YG       % Write image to that file


MATL, 36 29 bytes

5l$rtP+!kllII$r*O16tQ/XE'a'YG


This saves the result in file a.png.

Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file:

5l$rtP+!kllII$r*O16tQ/XE2YG


Here's an example output: Explanation

5l$r % 5×5 matrix of independent random values with uniform distribution % on the interval (0,1) tP+! % Duplicate, flip vertically, add, transpose. This gives a horizontally % symetric matrix. Center column pixels are uniformly distributed on the % interval (0,2). Rest have a triangular distribution on (0,2) k % Round down. In either of the above cases, this gives 0 and 1 % with the same probability llII$r   % 1×1×3 array of independent random numbers with uniform distribution
% on (0,1). This is the foreground color.
*        % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the
% 5×5 array become the random foreground color. Zeros remain as zeros.
O        % Push 0
16tQ/    % 16, duplicate, add 1, divide: gives 16/17, or 240/155
XE       % Replace 0 by 16/17: background color
'a'      % Push file name
YG       % Write image to that file

3 deleted 16 characters in body

MATL, 36 29 bytes

5l$rtP+!kllII$r*O16tQ/XE'a'YG


This saves the result in file a.png.

Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file:

5l$rtP+!kllII$r*O16tQ/XE2YG


Here's an example output: Explanation (to be updated)

H5H$r5l$r     % 2×55×5 arraymatrix of independent random numbersvalues with uniform distribution on (0,1)
l5H$r % 1×5 array of independent random numbers with% uniformon distributionthe oninterval (0,1) ytP+! % Duplicate, flip %vertically, Duplicateadd, thetranspose. firstThis arraygives a vertically P % Flipsymetric vertically vmatrix. Center row pixels are uniformly distributed on %the Concatenate the three arrays vertically % interval (0,2). GivesRest have a 5×5triangular array Ekdistribution on (0,2) k % Multiply by 2,% roundRound down:. givesIn 0either orof 1the equiprobably !above cases, this gives 0 and 1 % Transpose so that the array has% horizontalwith (notthe vertical)same symmetry.probability llII$r   % 1×1×3 array of independent random numbers with uniform distribution
% on (0,1). This is the foreground color.
*        % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the
% 5×5 array become the random foreground color. Zeros remain as zeros.
O        % Push 0
16tQ/    % 16, duplicate, add 1, divide: gives 16/17, or 240/155
XE       % Replace 0 by 16/17: background color
'a'      % Push file name
YG       % Write image to that file


MATL, 36 29 bytes

5l$rtP+!kllII$r*O16tQ/XE'a'YG


This saves the result in file a.png.

Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file:

5l$rtP+!kllII$r*O16tQ/XE2YG


Here's an example output: Explanation (to be updated)

H5H$r % 2×5 array of independent random numbers with uniform distribution on (0,1) l5H$r    % 1×5 array of independent random numbers with uniform distribution on (0,1)
y        % Duplicate the first array
P        % Flip vertically
v        % Concatenate the three arrays vertically. Gives a 5×5 array
Ek       % Multiply by 2, round down: gives 0 or 1 equiprobably
!        % Transpose so that the array has horizontal (not vertical) symmetry.
llII$r % 1×1×3 array of independent random numbers with uniform distribution % on (0,1). This is the foreground color. * % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the % 5×5 array become the random foreground color. Zeros remain as zeros. O % Push 0 16tQ/ % 16, duplicate, add 1, divide: gives 16/17, or 240/155 XE % Replace 0 by 16/17: background color 'a' % Push file name YG % Write image to that file  MATL, 36 29 bytes 5l$rtP+!kllII$r*O16tQ/XE'a'YG  This saves the result in file a.png. Replacing 'a' by 2 in the code displays the image (scaled up) instead of saving a file: 5l$rtP+!kllII$r*O16tQ/XE2YG  Here's an example output: Explanation 5l$r     % 5×5 matrix of independent random values with uniform distribution
% on the interval (0,1)
tP+!     % Duplicate, flip vertically, add, transpose. This gives a vertically
% symetric matrix. Center row pixels are uniformly distributed on the
% interval (0,2). Rest have a triangular distribution on (0,2)
k        % Round down. In either of the above cases, this gives 0 and 1
% with the same probability
llII\$r   % 1×1×3 array of independent random numbers with uniform distribution
% on (0,1). This is the foreground color.
*        % Multiply the two arrays with broadcast. Gives a 5×5×3 array. Ones in the
% 5×5 array become the random foreground color. Zeros remain as zeros.
O        % Push 0
16tQ/    % 16, duplicate, add 1, divide: gives 16/17, or 240/155
XE       % Replace 0 by 16/17: background color
'a'      % Push file name
YG       % Write image to that file

2 added 10 characters in body
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