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Re: How to specify the data-range with Import

• To: mathgroup at smc.vnet.net
• Subject: [mg122940] Re: How to specify the data-range with Import
• From: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>
• Date: Thu, 17 Nov 2011 06:05:24 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201111110953.EAA08442@smc.vnet.net>

Hi,

Jesus Hernandez and (maybe others) from the Wolfram support uncovered
the reason for this behavoir. The important detail here seems to be
whether or not the created list is a PackedArray. Since Range[5] gives a
packed array but Table[i,{i,5}] not, the following (from the example
below)

Import["lena_multi.tif", {"Data", Range[5]}] // Dimensions

does not work, while this here

Import["lena_multi.tif", {"Data", Table[i,{i,5}]}] // Dimensions

works as expected. Therefore, one has to use FromPackedArray from the
Developer package to use any arbitrarily created list of integers. For
instance 

Needs["Developer`"]
Import["lena_multi.tif", {"Data", 
  FromPackedArray@Range[3]}] // Dimensions

Cheers
Patrick

On Fri, 2011-11-11 at 04:53 -0500, Patrick Scheibe wrote:
> Hi,
> 
> following (old) example of a multi-image
> 
> img = ColorConvert[ExampleData[{"TestImage", "Lena"}], "Grayscale"];
> Export["lena_multi.tif", Table[img, {10}], "TIFF"];
> 
> With Import one can now specify that only the "Data" of the first 3
> images are required:
> 
> In[45]:= Import["lena_multi.tif", {"Data", {1, 2, 3}}] // Dimensions
> 
> Out[45]= {3, 512, 512}
> 
> works like a charm. But trying to import 50 of say 1000 images is
> slightly cumbersome this way. And now the fun starts:
> 
> Import["lena_multi.tif", {"Data", Range[3]}] // Dimensions
> 
> gives 
> 
> Import::noelem: The Import element "FrameNum" is not present when
> importing as TIFF. >>
> 
> maybe Import has some Hold attribute (which it *doesn't*)
> 
> Import["lena_multi.tif", Evaluate[{"Data", Range[3]}]] // Dimensions
> 
> doesn't work
> 
> With[{range = Range[3]},
>  Import["lena_multi.tif", {"Data", range}] // Dimensions
> ]
> 
> doesn't work. And so on and so on.. Luckily, we this very intuitive
> construct
> 
> In[50]:= Release[
>   Hold[Import["tmp/lena_multi.tif", {"Data", range}]] /. 
>    range -> Range[3]] // Dimensions
> 
> Out[50]= {3, 512, 512}
> 
> 
> Please, could someone enlighten me?
> 
> Cheers
> Patrick
> 
> PS: My system here is Linux-x86-64 with Ubuntu 10.04 and Mathematica 8.0.4
> 
> 
> 
> 

• References:
  • How to specify the data-range with Import
    • From: Patrick Scheibe <pscheibe@trm.uni-leipzig.de>