Download images only when not present on disk and print warning messages when converting unsupported pixel format.

[codemzs]

fixes #3631
fixes #3638

[codecov]

Codecov Report

Merging #3625 into master will increase coverage by <.01%.
The diff coverage is 85.5%.

@@            Coverage Diff             @@
##           master    #3625      +/-   ##
==========================================
+ Coverage   72.78%   72.78%   +<.01%     
==========================================
  Files         808      808              
  Lines      145548   145588      +40     
  Branches    16248    16250       +2     
==========================================
+ Hits       105931   105961      +30     
- Misses      35195    35203       +8     
- Partials     4422     4424       +2

Flag	Coverage Δ
#Debug	72.78% <85.5%> (ø)	⬆️
#production	68.28% <90.47%> (-0.01%)	⬇️
#test	89.04% <83.33%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
...c/Microsoft.ML.SamplesUtils/SamplesDatasetUtils.cs	24.34% <0%> (-0.12%)	⬇️
src/Microsoft.ML.ImageAnalytics/ImageLoader.cs	83.03% <100%> (-1.52%)	⬇️
src/Microsoft.ML.ImageAnalytics/ImageGrayscale.cs	78.68% <100%> (+0.35%)	⬆️
...rosoft.ML.ImageAnalytics/VectorToImageTransform.cs	76.83% <100%> (+0.06%)	⬆️
...Microsoft.ML.ImageAnalytics/ImagePixelExtractor.cs	82.93% <100%> (+0.2%)	⬆️
src/Microsoft.ML.ImageAnalytics/ImageResizer.cs	85.71% <100%> (+0.3%)	⬆️
...cenariosWithDirectInstantiation/TensorflowTests.cs	90.22% <83.33%> (-0.61%)	⬇️
src/Microsoft.ML.Transforms/Text/LdaTransform.cs	89.26% <0%> (-0.63%)	⬇️
...soft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs	84.9% <0%> (+0.2%)	⬆️
...soft.ML.TestFramework/DataPipe/TestDataPipeBase.cs	73.93% <0%> (+0.32%)	⬆️

[TomFinley]

                            throw Host.Except($"Image {src.ToString()} was not found.");

Not your code, but there's something a bit odd about it that it assumes that any exception must be due to teh file not being found. #Closed

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Refers to: src/Microsoft.ML.ImageAnalytics/ImageLoader.cs:208 in 133fbe1. [](commit_id = 133fbe1, deletion_comment = False)

[eerhardt]

Looks good, after @TomFinley's comments are addressed.

[codemzs]

                            throw Host.Except($"Image {src.ToString()} was not found.");

Seems like the comment above this line explains why the original author wrote like.

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In reply to: 488380679 [](ancestors = 488380679)

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Refers to: src/Microsoft.ML.ImageAnalytics/ImageLoader.cs:208 in 133fbe1. [](commit_id = 133fbe1, deletion_comment = False)

[codemzs]

                            throw Host.Except($"Image {src.ToString()} was not found.");

Spoke offline and we decided the to remove try catch altogether. Right now docs do say on file not found it will throw FileNotFoundException instead of ArgumentException as before..

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In reply to: 488396420 [](ancestors = 488396420,488380679)

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Refers to: src/Microsoft.ML.ImageAnalytics/ImageLoader.cs:208 in 133fbe1. [](commit_id = 133fbe1, deletion_comment = False)

[TomFinley]

Thanks @codemzs !

[glebuk]