[FWTools] Compress Ecw like Ermapper free compressor

toni-10 fiorenontaglio at libero.it
Tue Jun 24 07:20:42 EDT 2008

Is it any way to control the output of gdal_translate to Ecw in the same way
offered by the ErMapper free compressor 7.0?

In ErMapper compressor I can define:
1)Compression color to RGB
  From help file I read: The compression engine internally
  converts the RGB color image into YUV color space,
  specifically the one defined as the "JPEG Digital version
  of YUV". YUV is a color space that separates out intensity
  (Y) from chromatic or color changes (U and V). This enables
  more efficient compression of color imagery, ensuring that
  detail is preserved. The RGB to YUV conversion is
  automatic, and is automatically reversed during 
  decompression; the user always sees the file as a RGB file.

2)Desired compression ratio: this is not the actual compression ratio (eg
1/10 = from 100mb to 10mb) but the target compression ratio, meaning "how
much of the high frequencies info will be discarded"

In gdal_translate I have different controls such as
"-co TARGET=percent" but this is not the same as "Desired compression ratio"
meaning infact "the target size reduction as a percentage of the original".
...I don't know about RGB but the gdal_translate guide tells me that the ecw
conversion "reads any number of bands but returns only as eight bit image
data". Is it possibile, maybe with other utilities, to do what the ErMapper
compressor does?

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