Raster flips our image upside down

Question

We are working with this image:

And we are trying a project with singular value decomposition. Here is our approach:

We start by importing the image, which has this filename on our system, but it is the image above.

image = Import["DSC_0880-7.jpg"]

Then we do this:

A = ImageData[ImageTake[image, {1, 480}, {1, 640}], "Byte"];

Then we adjusted something we found on the web to help us:

Approximate[A_, k_] := Module[
   {approximateImage},
   {U, Σ, VT} = SingularValueDecomposition[N[A], k];
   approximateImage = Graphics[
     Raster[
      U.Σ.Transpose[VT]/
       Max[U.Σ.Transpose[VT]]],
     PlotLabel -> 
      "Singular Values: " <> ToString[NumberForm[k, 3]] <> 
       "     Compression: " <>
       ToString[
        NumberForm[
         100*
          k*(1. Dimensions[A][[1]] + 
             Dimensions[A][[2]])/(Dimensions[A][[1]]*
             Dimensions[A][[2]])
          "% of Original.", 2]
        ]
     ]
   ];

Then we try this:

Show[Approximate[A, 20]]

But our image is flipped upside down.

Can someone help us unflip our image?

Please read the relevant answer in What are the most common pitfalls awaiting new users?, hopefully it will clear things up. I don't think there's much to do about it, other than flipping it back. — C. E., Oct 28 '16 at 21:06

score 6 · Answer 1 · answered Oct 28 '16 at 21:15

6

Use the DataReversed option of ImageData.

img = ExampleData[{"TestImage", "Sailboat"}];

Graphics[Raster@ImageData[img, DataReversed -> True]]

This discrepancy between Image and Raster is due to the differences in standard coordinate systems in image processing / matrices (top to bottom) and function plotting ($y$ axis points up):

http://reference.wolfram.com/language/tutorial/ImageProcessing.html#1708646374

answered Oct 28 '16 at 21:15

Szabolcs

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@Szaboics Thanks to the help. My student really appreciated the response. – David Oct 29 '16 at 02:35

Raster flips our image upside down

1 Answers1