TIFF with only a channel and values

[dayer]

Hi,

I'm looking for get a file in TIFF format and only with a channel. Red channel for example, single band, because I'll need for georeference and get pixel values.
Firstly I've replaced the colours by anothers. For example one colour to rgb(12,12,12), another to rgb(18,18,18), rgb(24,24,24), rgb(30,30,30),... And secondly I try to get a TIFF single band with:

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convert prueba.tiff -channel R -separate prueba-R.tiff

But when I check it with gdalinfo it says it's three bands:

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Band 1 Block=480x2 Type=UInt16, ColorInterp=Red
[...]
Band 2 Block=480x2 Type=UInt16, ColorInterp=Green
Band 3 Block=480x2 Type=UInt16, ColorInterp=Blue

And identify -verbose says:

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[...]
  Channel statistics:
    Red:
      min: 3084 (0.0470588)
      max: 65535 (1)
      mean: 62746.7 (0.957453)
      standard deviation: 12821.5 (0.195643)
      kurtosis: 17.2132
      skewness: -4.38243
    Green:
      min: 3084 (0.0470588)
      max: 65535 (1)
      mean: 62746.7 (0.957453)
      standard deviation: 12821.5 (0.195643)
      kurtosis: 17.2132
      skewness: -4.38243
    Blue:
      min: 3084 (0.0470588)
      max: 65535 (1)
      mean: 62746.7 (0.957453)
      standard deviation: 12821.5 (0.195643)
      kurtosis: 17.2132
      skewness: -4.38243
[...]

However, if I try doing this in GIMP, split it in components in layers, delete all layers except Red channel, I get a TIFF only with a band.
gdalinfo says:

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[...]
Band 1 Block=480x64 Type=Byte, ColorInterp=Gray

identify -verbose says:

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[...]
  Channel statistics:
    Gray:
      min: 12 (0.0470588)
      max: 255 (1)
      mean: 244.151 (0.957453)
      standard deviation: 49.8889 (0.195643)
      kurtosis: 17.2132
      skewness: -4.38243
[...]

Then, I try with convert and -type palette and gdalinfo says:

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[...]
Band 1 Block=480x34 Type=Byte, ColorInterp=Palette
  Image Structure Metadata:
    NBITS=4
  Color Table (RGB with 16 entries)
    0: 12,12,12,255
    1: 18,18,18,255
    2: 24,24,24,255
    3: 30,30,30,255
    4: 36,36,36,255
    5: 42,42,42,255
    6: 48,48,48,255
    7: 255,255,255,255
    8: 0,0,0,255
    9: 0,0,0,255
   10: 0,0,0,255
   11: 0,0,0,255
   12: 0,0,0,255
   13: 0,0,0,255
   14: 0,0,0,255
   15: 0,0,0,255

Well. But ¿I could get other values for each pixel? For example:

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    0: 255,255,255
    12: 12,12,12,255
    18: 18,18,18,255
    24: 24,24,24,255
    30: 30,30,30,255
    36: 36,36,36,255
[...]

Thank you very much.

[snibgo]

For me, IM 6.7.9-Q16 on Windows 7:

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convert rose.tiff -channel R -separate rose-r.tiff

gives a greyscale (single channel) file. What version IM and platform are you on?

[fmw42]

In IM 6 any single channel (or grayscale) image will always be 3 equal R,G,B channels. IM 7 will have true single channel images.