Add support for GreyScale Jpeg

@@ -16,6 +16,7 @@
 - Simplify PdfImage constructor
 - Implement Image orientation
 - Add Exif reader
+- Add support for GreyScale Jpeg
 
 ## 1.3.23
 

@@ -205,6 +205,7 @@ class PDFImage extends PdfImage {
             height: height,
             alpha: alpha,
             alphaChannel: false,
+            isRGB: true,
             jpeg: false,
             orientation: PdfImageOrientation.topLeft);
 }

@@ -24,6 +24,7 @@ class PdfJpegInfo {
 
     int width;
     int height;
+    int color;
     int offset = 0;
     while (offset < buffer.lengthInBytes) {
       while (buffer.getUint8(offset) == 0xff) {
@@ -55,6 +56,7 @@ class PdfJpegInfo {
       if (mrkr == 0xc0) {
         height = buffer.getUint16(offset + 1);
         width = buffer.getUint16(offset + 3);
+        color = buffer.getUint8(offset + 5);
         break;
       }
       offset += len - 2;
@@ -62,15 +64,19 @@ class PdfJpegInfo {
 
     final Map<PdfExifTag, dynamic> tags = _findExifInJpeg(buffer);
 
-    return PdfJpegInfo._(width, height, tags);
+    return PdfJpegInfo._(width, height, color, tags);
   }
 
-  PdfJpegInfo._(this.width, this.height, this.tags);
+  PdfJpegInfo._(this.width, this.height, this._color, this.tags);
 
   final int width;
 
   final int height;
 
+  final int _color;
+
+  bool get isRGB => _color == 3;
+
   final Map<PdfExifTag, dynamic> tags;
 
   /// EXIF version

@@ -51,6 +51,7 @@ class PdfImage extends PdfXObject {
         height: height,
         alpha: alpha,
         alphaChannel: false,
+        isRGB: true,
         jpeg: false,
         orientation: orientation,
       );
@@ -62,12 +63,14 @@ class PdfImage extends PdfXObject {
     @required int height,
     @required this.alpha,
     @required this.alphaChannel,
+    @required this.isRGB,
     @required this.jpeg,
     @required this.orientation,
   })  : assert(alphaChannel == false || alpha == true),
         assert(width != null),
         assert(height != null),
         assert(jpeg != null),
+        assert(isRGB != null),
         assert(orientation != null),
         _width = width,
         _height = height,
@@ -86,16 +89,17 @@ class PdfImage extends PdfXObject {
         height: height,
         alpha: alpha,
         alphaChannel: true,
+        isRGB: false,
         jpeg: jpeg,
         orientation: orientation,
       );
       params['/SMask'] = PdfStream.string('${_sMask.objser} 0 R');
     }
 
-    if (alphaChannel) {
-      params['/ColorSpace'] = PdfStream.string('/DeviceGray');
-    } else {
+    if (isRGB) {
       params['/ColorSpace'] = PdfStream.string('/DeviceRGB');
+    } else {
+      params['/ColorSpace'] = PdfStream.string('/DeviceGray');
     }
 
     if (jpeg) {
@@ -118,6 +122,7 @@ class PdfImage extends PdfXObject {
       height: info.height,
       jpeg: true,
       alpha: false,
+      isRGB: info.isRGB,
       alphaChannel: false,
       orientation: orientation ?? info.orientation,
     );
@@ -145,6 +150,9 @@ class PdfImage extends PdfXObject {
   /// The image data is a jpeg image
   final bool jpeg;
 
+  /// The image data is a color RGB image
+  final bool isRGB;
+
   /// The internal orientation of the image
   final PdfImageOrientation orientation;