Simply use images with more resolution - more elements. A 20x20 image is too small to get good resolution of a binary image made from lines.
% Demo by Image Analyst.
clc; % Clear command window.
clear; % Delete all variables.
close all; % Close all figure windows except those created by imtool.
workspace; % Make sure the workspace panel is showing.
w = 200;
h = 200;
blankImage= 255*ones(w,h,3,'uint8');
position_x = (w+1)/2;
position_y = (h+1)/2;
font_start = 50;
font_end = 200;
num_fontsA = round(linspace(font_start, font_end, 4))
numImagesA = length(num_fontsA)
A = cell(1, numImagesA);
for i=1:numImagesA
for font_size = num_fontsA(i)
img= insertText(blankImage,[position_x position_y],'A','Font','Times New Roman','FontSize',font_size,'TextColor','black','BoxColor','w','BoxOpacity',0,'AnchorPoint','Center');
img= rgb2gray(img);
A{i} = img;
subplot(2,2,i);
imshow(A{i});
axis on;
title("A with font size " + font_size);
end
end
