From 9d4ecaaf728135e761a34ece10535366f444a0e9 Mon Sep 17 00:00:00 2001
From: Joscha <joscha@plugh.de>
Date: Fri, 15 Mar 2024 22:13:45 +0100
Subject: [PATCH] Print images lighter

---
 showbits-common/src/widgets/image.rs   | 16 ++++++----------
 showbits-thermal-printer/src/drawer.rs | 22 +++++++++++++++++++---
 2 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/showbits-common/src/widgets/image.rs b/showbits-common/src/widgets/image.rs
index 2a517c1..a3474ec 100644
--- a/showbits-common/src/widgets/image.rs
+++ b/showbits-common/src/widgets/image.rs
@@ -3,7 +3,7 @@ use image::{
     RgbaImage,
 };
 use mark::dither::{AlgoFloydSteinberg, AlgoStucki, Algorithm, DiffEuclid, Palette};
-use palette::{IntoColor, Srgb, Srgba};
+use palette::{IntoColor, LinSrgb, Srgba};
 use taffy::prelude::{AvailableSpace, Layout, Size};
 
 use crate::Widget;
@@ -15,12 +15,12 @@ pub enum DitherAlgorithm {
 }
 
 impl DitherAlgorithm {
-    fn dither(self, image: RgbaImage, palette: &Palette<Srgb>) -> RgbaImage {
+    fn dither(self, image: RgbaImage, palette: &Palette<LinSrgb>) -> RgbaImage {
         match self {
             Self::FloydSteinberg => {
-                <AlgoFloydSteinberg as Algorithm<Srgb, DiffEuclid>>::run(image, palette)
+                <AlgoFloydSteinberg as Algorithm<LinSrgb, DiffEuclid>>::run(image, palette)
             }
-            Self::Stucki => <AlgoStucki as Algorithm<Srgb, DiffEuclid>>::run(image, palette),
+            Self::Stucki => <AlgoStucki as Algorithm<LinSrgb, DiffEuclid>>::run(image, palette),
         }
     }
 }
@@ -31,11 +31,7 @@ pub struct Image {
     grow: bool,
     filter: FilterType,
 
-    // The palette uses Srgb instead of LinSrgb because dithering in Srgb
-    // produces better results when printed, even though color distance
-    // calculations are objectively wrong. Maybe the printer's black ink
-    // behaviour makes them correct again.
-    dither_palette: Option<Palette<Srgb>>,
+    dither_palette: Option<Palette<LinSrgb>>,
     dither_algorithm: DitherAlgorithm,
 }
 
@@ -70,7 +66,7 @@ impl Image {
         let palette = palette
             .iter()
             .map(|c| c.color.into_color())
-            .collect::<Vec<Srgb>>();
+            .collect::<Vec<LinSrgb>>();
 
         self.dither_palette = Some(Palette::new(palette));
         self
diff --git a/showbits-thermal-printer/src/drawer.rs b/showbits-thermal-printer/src/drawer.rs
index 4c88c26..29b109f 100644
--- a/showbits-thermal-printer/src/drawer.rs
+++ b/showbits-thermal-printer/src/drawer.rs
@@ -1,6 +1,6 @@
 mod calendar;
 
-use image::RgbaImage;
+use image::{Luma, Pixel, RgbaImage};
 use showbits_common::{
     color::{BLACK, WHITE},
     widgets::{Block, FontStuff, HasFontStuff, Image, Text},
@@ -131,9 +131,17 @@ impl Drawer {
         Ok(())
     }
 
-    fn on_image(&mut self, image: RgbaImage) -> anyhow::Result<()> {
+    fn on_image(&mut self, mut image: RgbaImage) -> anyhow::Result<()> {
         let mut tree = Tree::<Context>::new(WHITE);
 
+        for pixel in image.pixels_mut() {
+            let [l] = pixel.to_luma().0;
+            let l = l as f32 / 255.0; // Convert to [0, 1]
+            let l = 1.0 - (0.4 * (1.0 - l)); // Lerp to [0.6, 1]
+            let l = (l.clamp(0.0, 1.0) * 255.0) as u8; // Convert back to [0, 255]
+            *pixel = Luma([l]).to_rgba();
+        }
+
         let image = Image::new(image)
             .with_dither_palette(&[BLACK, WHITE])
             .node()
@@ -152,9 +160,17 @@ impl Drawer {
         Ok(())
     }
 
-    fn on_photo(&mut self, image: RgbaImage, title: String) -> anyhow::Result<()> {
+    fn on_photo(&mut self, mut image: RgbaImage, title: String) -> anyhow::Result<()> {
         let mut tree = Tree::<Context>::new(WHITE);
 
+        for pixel in image.pixels_mut() {
+            let [l] = pixel.to_luma().0;
+            let l = l as f32 / 255.0; // Convert to [0, 1]
+            let l = 1.0 - (0.4 * (1.0 - l)); // Lerp to [0.6, 1]
+            let l = (l.clamp(0.0, 1.0) * 255.0) as u8; // Convert back to [0, 255]
+            *pixel = Luma([l]).to_rgba();
+        }
+
         let image = Image::new(image)
             .with_dither_palette(&[BLACK, WHITE])
             .node()