Add Transparent Pixel Support and Minor Fixes.

src/charsets.rs

@@ -26,7 +26,7 @@ pub const SLIGHT: &[&str] = &[
     "\\\\", "/", "Y", "L", "p", "d", "a", "*", "W", "8", "%", "@", "$",
 ];
 pub const MINIMAL: &[&str] = &[
-    " ", " ", ".", ":", "'", ";", "o", "l", "d", "c", "x", "0", "k", "K", "N",  "M","W", "X",
+    " ", " ", ".", ":", "'", ";", "o", "l", "d", "c", "x", "0", "k", "K", "N", "M", "W", "X",
 ];
 
 pub fn from_str(s: &str) -> Option<&[&str]> {

src/image_renderer.rs

@@ -1,4 +1,4 @@
-use std::io;
+use std::{io, u8};
 
 use ansi_term::Color;
 use image::{DynamicImage, Rgba};
@@ -13,9 +13,14 @@ pub struct ImageRenderer<'a> {
 impl ImageRenderer<'_> {
     fn get_char_for_pixel(&self, pixel: &Rgba<u8>, maximum: f64) -> &str {
         let as_grayscale = self.get_grayscale(pixel) / maximum;
+        let transparency_percent = self.get_transparency_percent(pixel);
 
-        // TODO: Use alpha channel to determine if pixel is transparent?
-        let char_index = (as_grayscale * (self.options.charset.len() as f64 - 1.0)) as usize;
+        let char_index = if transparency_percent < 0.95 {
+            // if we have at least 95% transparency, count this pixel as transparent and give minimum index
+            0
+        } else {
+            (as_grayscale * (self.options.charset.len() as f64 - 1.0)) as usize
+        };
 
         self.options.charset[if self.options.invert {
             self.options.charset.len() - 1 - char_index
@@ -24,6 +29,10 @@ impl ImageRenderer<'_> {
         }]
     }
 
+    fn get_transparency_percent(&self, pixel: &Rgba<u8>) -> f64 {
+        pixel[3] as f64 / u8::MAX as f64
+    }
+
     fn get_grayscale(&self, pixel: &Rgba<u8>) -> f64 {
         ((pixel[0] as f64 * 0.299) + (pixel[1] as f64 * 0.587) + (pixel[2] as f64 * 0.114)) / 255.0
     }