Improve error message when trying to decode JPEG lossless images on t…

…he CPU backend (NVIDIA#4587)

Signed-off-by: Joaquin Anton <janton@nvidia.com>

dali/imgcodec/decoders/opencv_fallback.cc

@@ -1,4 +1,4 @@
-// Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// Copyright (c) 2022-2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 #include "dali/imgcodec/decoders/opencv_fallback.h"
 #include "dali/imgcodec/util/convert.h"
 #include "dali/imgcodec/registry.h"
+#include "dali/imgcodec/parsers/jpeg.h"
 
 namespace dali {
 namespace imgcodec {
@@ -123,6 +124,23 @@ DecodeResult OpenCVDecoderInstance::DecodeImplTask(int thread_idx,
       TensorLayout layout = cvimg.dims == 3 ? "DHWC" : "HWC";
 
       Convert(out, layout, out_format, in, layout, in_format, roi, orientation);
+    } else {
+      JpegParser jpeg_parser{};
+      if (jpeg_parser.CanParse(in)) {
+        auto ext_info = jpeg_parser.GetExtendedInfo(in);
+        std::array<uint8_t, 2> sof3_marker = {0xff, 0xc3};
+        if (ext_info.sof_marker == sof3_marker) {
+          res.exception = std::make_exception_ptr(
+            std::runtime_error(
+              make_string(
+                "Failed to decode a JPEG lossless (SOF-3) sample: ", in->SourceInfo(), ".\n"
+                "Support for lossless is currently very limited:\n"
+                "- Only number of components <= 2\n"
+                "- Only predictor value 1\n"
+                "- Only \"mixed\" backend\n"
+                "If you used the \"cpu\" backend, please try the \"mixed\" one instead\n")));
+        }
+      }
     }
   } catch (...) {
     res.exception = std::current_exception();

dali/imgcodec/parsers/jpeg.cc

@@ -1,4 +1,4 @@
-// Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// Copyright (c) 2022-2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -43,7 +43,11 @@ bool IsSofMarker(const jpeg_marker_t &marker) {
 }
 
 ImageInfo JpegParser::GetInfo(ImageSource *encoded) const {
-  ImageInfo info{};
+  return GetExtendedInfo(encoded).img_info;
+}
+
+JpegParser::ExtendedImageInfo JpegParser::GetExtendedInfo(ImageSource *encoded) const {
+  JpegParser::ExtendedImageInfo info{};
   auto stream = encoded->Open();
 
   jpeg_marker_t first_marker = stream->ReadOne<jpeg_marker_t>();
@@ -67,11 +71,12 @@ ImageInfo JpegParser::GetInfo(ImageSource *encoded) const {
     uint16_t size = ReadValueBE<uint16_t>(*stream);
     ptrdiff_t next_marker_offset = stream->TellRead() - 2 + size;
     if (IsSofMarker(marker)) {
+      info.sof_marker = marker;
       stream->Skip(1);  // Skip the precision field
       auto height = ReadValueBE<uint16_t>(*stream);
       auto width = ReadValueBE<uint16_t>(*stream);
       auto nchannels = stream->ReadOne<uint8_t>();
-      info.shape = {height, width, nchannels};
+      info.img_info.shape = {height, width, nchannels};
       read_shape = true;
     } else if (marker == app1_marker && stream->ReadOne<jpeg_exif_header_t>() == exif_header) {
       std::vector<uint8_t> exif_block(size - 8);
@@ -81,7 +86,8 @@ ImageInfo JpegParser::GetInfo(ImageSource *encoded) const {
         continue;
       auto entry = reader.getTag(cv::ORIENTATION);
       if (entry.tag != cv::INVALID_TAG) {
-        info.orientation = FromExifOrientation(static_cast<ExifOrientation>(entry.field_u16));
+        info.img_info.orientation =
+            FromExifOrientation(static_cast<ExifOrientation>(entry.field_u16));
         read_orientation = true;
       }
     }

dali/imgcodec/parsers/jpeg.h

@@ -1,4 +1,4 @@
-// Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// Copyright (c) 2022-2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -24,6 +24,12 @@ class DLL_PUBLIC JpegParser : public ImageParser {
  public:
   ImageInfo GetInfo(ImageSource *encoded) const override;
   bool CanParse(ImageSource *encoded) const override;
+
+  struct ExtendedImageInfo {
+    ImageInfo img_info;
+    std::array<uint8_t, 2> sof_marker;
+  };
+  ExtendedImageInfo GetExtendedInfo(ImageSource *encoded) const;
 };
 
 }  // namespace imgcodec

dali/test/python/decoder/test_imgcodec.py

@@ -457,4 +457,7 @@ def pipe(file):
     imgfile = "db/single/jpeg_lossless/0/cat-1245673_640_grayscale_16bit.jpg"
     p = pipe(os.path.join(test_data_root, imgfile))
     p.build()
-    assert_raises(RuntimeError, p.run, glob='*')  # Add glob pattern when we have a meaningful error
+
+    assert_raises(
+        RuntimeError, p.run,
+        glob='*Failed to decode a JPEG lossless (SOF-3)*Only "mixed" backend*')