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graphics - how to Export raster data as a tiff unmolested


I feel certain there is a simple answere here.. how do I export image data to a tiff without any scaling?


I want to read back in the exact data.


g = Show[Graphics[{Black, Disk[#, 1]}] & /@ Table[RandomReal[{-10, 10}, 2], {50}]];
datain = ImageData[Rasterize[Style[g, Antialiasing -> False], "ColorSpace"-> "Grayscale"]];

as a more simple example just use:



datain = Table[0, {300}, {400}];

Export["test.tiff", Raster[datain], "BitDepth" -> 1, "ColorSpace" -> "Grayscale" ,
       ImageSize -> Reverse[Dimensions[datain]]];
dataout = Reverse[ImageData[Import["test.tiff"]]];
datain == dataout    ->> False
GraphicsGrid[{{
   Graphics[Raster[datain]],
   Graphics[Raster[dataout]], 
   Graphics[Raster[(1 + datain - dataout)/2]]}}]


enter image description here


What you see is the image has been shrunk to accomodate an white margin of about 10 pixels. (Most annoying you wouldn't notice this if you didn't look carefull..)


example 2..


enter image description here


Edit


Bill S has the solution.. Either Image[datain] or Image[Raster[datain]] or this mess:


Graphics[Raster[datain], 
      PlotRange -> {{0, Dimensions[datain][[2]]}, {0,Dimensions[datain][[1]]}}]


does the job. The last form I guess gives a clue, presumably Export calls Graphics which is padding by default. None of the documented options ImagePadding, ImageMargins, etc turn this off though.


Edit 2.. need BOTH of these options...go figure


Graphics[Raster[datain], ImagePadding -> None,  PlotRangePadding -> None]

Answer



One way to do this is to define your data as an image


datain=Image[Table[0, {300}, {400}];]

and then save the image as a tif


Export["test.tif", datain]


Now when you read it back in:


q = Import["test.tif"]

you can see that they are the same since


ImageData[q] == ImageData[datain]

Of course, this only works under certain conditions: the data has to be representable within the bit depth of the image -- this is inherent to the .tif format. Moreover, you will need to rescale the image so that all values lie between 0 and 1 in order to avoid truncation when saving to a .tif.


Here's an example. Create your data:


w = Image[RandomInteger[{0, 255}, {5, 5}]/255]


Note I've scaled everything between zero and one and the data will fit within a 8-bit depth.


Export["test.tif", w]
q = Import["test.tif"]

The data is intact, since


ImageData[q] == ImageData[w]

returns True.


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