Changed out dithering algorithm and added auto brighting

src/dithering.rs

@@ -1,44 +1,31 @@
-use image::DynamicImage;
+use image::{
+    DynamicImage, GrayImage,
+    imageops::{self, colorops},
+};
+pub fn auto_brighten(gray: &mut GrayImage) -> () {
+    let avg = gray.pixels().map(|p| p.0[0] as u32).sum::<u32>() / gray.len() as u32;
+
+    if avg < 100 {
+        colorops::brighten_in_place(gray, 40);
+        colorops::contrast_in_place(gray, 25.0);
+    } else if avg > 180 {
+        colorops::brighten_in_place(gray, -15);
+    }
+}
+
+pub fn dither(gray: &mut GrayImage) -> Vec<u8> {
+    imageops::dither(gray, &imageops::colorops::BiLevel);
 
-pub fn atkinson_mono(img: &DynamicImage) -> Vec<u8> {
-    let mut gray = img.to_luma8();
     let (w, h) = (gray.width() as usize, gray.height() as usize);
     let pitch = (w + 7) >> 3;
     let mut bits = vec![0u8; pitch * h];
-    let buf = gray.as_mut();
 
     for y in 0..h {
-        let row = y * w;
         for x in 0..w {
-            let i = row + x;
-            let old = buf[i];
-            let new = if old < 128 { 0 } else { 255 };
-            buf[i] = new;
-            let bit = new == 0;
-            if bit {
-                let byte = y * pitch + (x >> 3);
-                bits[byte] |= 128 >> (x & 7);
-            }
-            let err = ((old as i16) - (new as i16)) / 8;
-
-            if x + 1 < w {
-                buf[i + 1] = (buf[i + 1] as i16 + err).clamp(0, 255) as u8;
-            }
-            if x + 2 < w {
-                buf[i + 2] = (buf[i + 2] as i16 + err).clamp(0, 255) as u8;
-            }
-            if y + 1 < h {
-                let down = i + w;
-                if x > 0 {
-                    buf[down - 1] = (buf[down - 1] as i16 + err).clamp(0, 255) as u8;
-                }
-                buf[down] = (buf[down] as i16 + err).clamp(0, 255) as u8;
-                if x + 1 < w {
-                    buf[down + 1] = (buf[down + 1] as i16 + err).clamp(0, 255) as u8;
-                }
-                if y + 2 < h {
-                    buf[down + w] = (buf[down + w] as i16 + err).clamp(0, 255) as u8;
-                }
+            let byte = y * pitch + (x >> 3);
+            let bit = 7 - (x & 7);
+            if gray[(x as u32, y as u32)].0[0] == 0 {
+                bits[byte] |= 1 << bit;
             }
         }
     }

src/escpos.rs

@@ -1,5 +1,8 @@
-use crate::dithering::atkinson_mono;
-use image::{DynamicImage, imageops::FilterType};
+use crate::dithering::{auto_brighten, dither};
+use image::{
+    DynamicImage,
+    imageops::{FilterType, colorops},
+};
 
 const MAX_WIDTH: u32 = 384;
 
@@ -26,7 +29,10 @@ pub fn escpos_raster(
     let img = if swap { &img.rotate90() } else { &img };
     let img = img.resize(w, h, FilterType::Triangle);
 
-    let mono = atkinson_mono(&img);
+    let mut gray = img.to_luma8();
+    auto_brighten(&mut gray);
+
+    let mono = dither(&mut gray);
     let (width_px, height_px) = (img.width() as u16, img.height() as u16);
     let width_bytes = ((width_px + 7) >> 3) as u16;