From 1ab21307d631e7caf701e5b99a95a26f32ffbb97 Mon Sep 17 00:00:00 2001
From: lashman <lashman@robotbrush.com>
Date: Fri, 6 Mar 2026 16:53:32 +0200
Subject: [PATCH] Apply output DPI to JPEG files via mozjpeg pixel density

- Add output_dpi field to EncoderOptions
- Set JFIF pixel density header in JPEG output when DPI > 0
- Wire output_dpi from ProcessingJob through to encoder in both
  parallel and sequential execution paths
---
 pixstrip-core/src/encoder.rs  | 10 ++++++++++
 pixstrip-core/src/executor.rs |  2 ++
 2 files changed, 12 insertions(+)

diff --git a/pixstrip-core/src/encoder.rs b/pixstrip-core/src/encoder.rs
index acd1cbf..e354b00 100644
--- a/pixstrip-core/src/encoder.rs
+++ b/pixstrip-core/src/encoder.rs
@@ -8,6 +8,8 @@ use crate::types::{ImageFormat, QualityPreset};
 pub struct EncoderOptions {
     pub progressive_jpeg: bool,
     pub avif_speed: u8,
+    /// Output DPI (0 means don't set / use default)
+    pub output_dpi: u32,
 }
 
 pub struct OutputEncoder {
@@ -20,6 +22,7 @@ impl OutputEncoder {
             options: EncoderOptions {
                 progressive_jpeg: false,
                 avif_speed: 6,
+                output_dpi: 0,
             },
         }
     }
@@ -80,6 +83,13 @@ impl OutputEncoder {
         if self.options.progressive_jpeg {
             comp.set_progressive_mode();
         }
+        if self.options.output_dpi > 0 {
+            comp.set_pixel_density(mozjpeg::PixelDensity {
+                unit: mozjpeg::PixelDensityUnit::Inches,
+                x: self.options.output_dpi as u16,
+                y: self.options.output_dpi as u16,
+            });
+        }
 
         let mut output = Vec::new();
         let mut started = comp.start_compress(&mut output).map_err(|e| PixstripError::Processing {
diff --git a/pixstrip-core/src/executor.rs b/pixstrip-core/src/executor.rs
index 7c556c3..c476eef 100644
--- a/pixstrip-core/src/executor.rs
+++ b/pixstrip-core/src/executor.rs
@@ -185,6 +185,7 @@ impl PipelineExecutor {
                         let encoder = OutputEncoder::with_options(EncoderOptions {
                             progressive_jpeg: job.progressive_jpeg,
                             avif_speed: job.avif_speed,
+                            output_dpi: job.output_dpi,
                         });
 
                         match Self::process_single_static(job, source, &loader, &encoder, idx) {
@@ -243,6 +244,7 @@ impl PipelineExecutor {
         let encoder = OutputEncoder::with_options(EncoderOptions {
             progressive_jpeg: job.progressive_jpeg,
             avif_speed: job.avif_speed,
+            output_dpi: job.output_dpi,
         });
 
         let mut result = BatchResult {