I assumed that Image and ImageData are inverses, so that the following expression gives back the original image.
Image[ImageData[image]]
But that doesn't work. Why?
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1 Answer
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I would guess it's something to do with the ImageType.
img1 = ExampleData[{"TestImage", "Mandrill"}];
img2 = Image[ImageData[ExampleData[{"TestImage", "Mandrill"}]]];
img1 == img2
(* False *)
ImageType[img1]
(* Byte *)
ImageType[img2]
(* Real *)
However, trying the following doesn't seem to help:
img3 = Image[
ImageData[ExampleData[{"TestImage", "Mandrill"}], "Byte"], "Byte"];
ImageType[img3]
(* Byte *)
img3 == img1
(* False *)
But the following (courtesy of @george2079) does work! It must be related to the default option for Image being the following, rather than RGB, so the original colorspace is not preserved.
ColorSpace -> Automatictreats values as arbitrary channel intensities
img4 = Image[
ImageData[ExampleData[{"TestImage", "Mandrill"}], "Byte"], "Byte",
ColorSpace -> "RGB"]
img1 == img4
(* True *)
Hence the following code from @Kuba should work generally:
Image[ImageData[#, ImageType[#]], ImageType[#], Options[#]] &[img1]
answered Feb 26, 2016 at 19:52
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2$\begingroup$ puzzled myself.. this gets it back:
Image[ImageData[ExampleData[{"TestImage", "Mandrill"}], "Byte"], "Byte", ColorSpace -> "RGB"]$\endgroup$ Commented Feb 26, 2016 at 20:05 -
1$\begingroup$ probably more general:
img1 === Image[ImageData[#, ImageType[#]], ImageType[#], Options[#]] &[img1]$\endgroup$– KubaCommented Feb 26, 2016 at 20:08 -
$\begingroup$ Shouldn't the ColorSpace of RGB provide only 3 parameters? A black bmp image mentioned above comes with a
ColorSpaceof RGB, but theImageDatalooks like{{0,0,0,255},{0,0,0,255}...}. What does the 4th parameter do? $\endgroup$ Commented Feb 26, 2016 at 20:36 -
1$\begingroup$ @AntonAlice It denotes the transparency, or "alpha" value. $\endgroup$ Commented Feb 26, 2016 at 20:46
Image[ImageData[ExampleData[{"TestImage", "Mandrill"}]]]works fine... $\endgroup$Image[ImageData[ExampleData[{"TestImage", "Mandrill"}]]] == ExampleData[{"TestImage", "Mandrill"}]returns false. If you look atFullFormyou see the image color representation has changed from interger to float. $\endgroup$ImageTypeused byImageData." $\endgroup$