From bb620c8f0634bfbf06441188a0f749ada0bc8da6 Mon Sep 17 00:00:00 2001
From: John Whitington <john@coherentgraphics.co.uk>
Date: Mon, 1 Jan 2024 11:46:32 +0000
Subject: [PATCH] Extend PNG loading to greyscale and 16bpp

---
 Changes      |  1 +
 cpdfimage.ml | 30 +++++++++++++++---------------
 cpdfpng.ml   | 16 +++++++++++-----
 cpdfpng.mli  |  4 +++-
 4 files changed, 30 insertions(+), 21 deletions(-)

diff --git a/Changes b/Changes
index 44b4de2..e4988a5 100644
--- a/Changes
+++ b/Changes
@@ -24,6 +24,7 @@ Extended features:
 o -list-images-used[-json] extends -image-resolution
 o Use -raw with -extract-images to get PNMs
 o -extract-images can extract JBIG2 images and their globals
+o more PNGs - greyscale 1, 2, 4, 8, 16bpp and RGB 16bpp
 
 Fixes:
 
diff --git a/cpdfimage.ml b/cpdfimage.ml
index c792070..173d57d 100644
--- a/cpdfimage.ml
+++ b/cpdfimage.ml
@@ -429,21 +429,21 @@ let obj_of_jpeg_data data =
 
 let obj_of_png_data data =
   let png = Cpdfpng.read_png (Pdfio.input_of_bytes data) in
-  let d =
-    ["/Length", Pdf.Integer (Pdfio.bytes_size png.idat);
-     "/Filter", Pdf.Name "/FlateDecode";
-     "/Subtype", Pdf.Name "/Image";
-     "/BitsPerComponent", Pdf.Integer 8;
-     "/ColorSpace", Pdf.Name "/DeviceRGB";
-     "/DecodeParms", Pdf.Dictionary
-                      ["/BitsPerComponent", Pdf.Integer 8;
-                       "/Colors", Pdf.Integer 3;
-                       "/Columns", Pdf.Integer png.width;
-                       "/Predictor", Pdf.Integer 15];
-     "/Width", Pdf.Integer png.width;
-     "/Height", Pdf.Integer png.height]
-  in
-    Pdf.Stream {contents = (Pdf.Dictionary d, Pdf.Got png.idat)}, []
+    let d =
+      ["/Length", Pdf.Integer (Pdfio.bytes_size png.idat);
+       "/Filter", Pdf.Name "/FlateDecode";
+       "/Subtype", Pdf.Name "/Image";
+       "/BitsPerComponent", Pdf.Integer png.bitdepth;
+       "/ColorSpace", Pdf.Name (match png.colortype with 0 -> "/DeviceGray" | 2 -> "/DeviceRGB" | _ -> error "obj_of_png_data 1");
+       "/DecodeParms", Pdf.Dictionary
+                        ["/BitsPerComponent", Pdf.Integer png.bitdepth;
+                         "/Colors", Pdf.Integer (match png.colortype with 0 -> 1 | 2 -> 3 | _ -> error "obj_of_png_data 2");
+                         "/Columns", Pdf.Integer png.width;
+                         "/Predictor", Pdf.Integer 15];
+       "/Width", Pdf.Integer png.width;
+       "/Height", Pdf.Integer png.height]
+    in
+      Pdf.Stream {contents = (Pdf.Dictionary d, Pdf.Got png.idat)}, []
 
 let jbig2_dimensions data =
   (bget data 11 * 256 * 256 * 256 + bget data 12 * 256 * 256 + bget data 13 * 256 + bget data 14,
diff --git a/cpdfpng.ml b/cpdfpng.ml
index a55f56e..48d8c11 100644
--- a/cpdfpng.ml
+++ b/cpdfpng.ml
@@ -1,12 +1,15 @@
-(* Read non-interlaced, non-transparent 24 bit PNGs. Such a PNG may
+(* Read non-interlaced, non-transparent PNGs. Such a PNG may
    be loaded into a PDF simply by extracting its width and height from the
-   IHDR, and concatenating all its IDAT data sections together. *)
+   IHDR, and concatenating all its IDAT data sections together, and specifying
+   the appropriate Filter and Predictor.*)
 open Pdfutil
 open Pdfio
 
 type t =
   {width : int;
    height : int;
+   bitdepth : int;
+   colortype : int;
    idat : bytes}
 
 (* Writing *)
@@ -121,9 +124,8 @@ let read_png i =
     let width = read_unsigned_4byte hdr in
     let height = read_unsigned_4byte hdr in
     let bitdepth = hdr.input_byte () in
-    if bitdepth <> 8 then raise (Pdf.PDFError "read_png: bit depth not 8") else
     let colortype = hdr.input_byte () in
-    if colortype <> 2 then raise (Pdf.PDFError "read_png: only 24 bit non-alpha PNGs") else
+    if colortype <> 2 && colortype <> 0 then raise (Pdf.PDFError "read_png: only non-alpha non-palette PNGs") else
     let _ (*compressionmethod*) = hdr.input_byte () in
     let _ (*filtermethod*) = hdr.input_byte () in
     let interlacemethod = hdr.input_byte () in
@@ -137,6 +139,10 @@ let read_png i =
       with
         _ -> ()
       end;
-      {width = i32toi width; height = i32toi height; idat = concat_bytes (rev !idat)}
+      {width = i32toi width;
+       height = i32toi height;
+       colortype;
+       bitdepth;
+       idat = concat_bytes (rev !idat)}
   with
     e -> raise (Pdf.PDFError (Printf.sprintf "read_png: failed on %s" (Printexc.to_string e)))
diff --git a/cpdfpng.mli b/cpdfpng.mli
index 6729e46..d8247bf 100644
--- a/cpdfpng.mli
+++ b/cpdfpng.mli
@@ -4,7 +4,9 @@
 type t =
   {width : int;
    height : int;
+   bitdepth : int;
+   colortype : int;
    idat : Pdfio.bytes}
 
-(** Read a non-interlaced, non-transparent 24 bit PNG for inclusion in a PDF file. *)
+(** Read a non-interlaced, non-alpha, non-palette PNG for inclusion in a PDF file. *)
 val read_png : Pdfio.input -> t