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Thread: How to export lossless raster with same quality as source?

  1. #1
    Thomas Lupher
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    Question How to export lossless raster with same quality as source?

    So I have a bunch of single-band 1500x1500 cell 1x1meter 32bit-float lzw-compressed rasters in TIFF format I am trying to export as uncompressed to the same quality as their sources.

    Why do the uncompressed TIFF's render as lower quality than compressed originals? I know TIFF is lossless and that there is no compression quality setting so I don't know why they are looking worse...

    Below is a comparison of Source and Export output attributes. Why are the cell statistics different if the source and output files are in a lossless file format?
    Click image for larger version

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    Attached Thumbnails Attached Thumbnails Click image for larger version

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    Last edited by tlupher; 05-01-2012 at 08:47 AM. Reason: added an example

  2. #2
    Jeff Swain

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    Default Re: How to export lossless raster with same quality as source?

    Can you provide a visual example of what you mean by loss of 'quality?' From the source statistics should be nearly identical. I would consider the display resampling and perhaps make a copy of the original and generate statistics. Another test would be to import the statistics from the source to the exported one and see if look is the same.

    Also can you identify pixels in both rasters and compare the results. Since you are not changing the coordinate system, I do not think that values should be altered due to resampling, unless you are altering the spatial extent of the raster.
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  3. #3
    Thomas Lupher
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    Default Re: How to export lossless raster with same quality as source?

    I found the problem was my misunderstanding of rasters and the general rendering process in ArcMap. I learned ArcMap stretches imported rasters causing them to look super bright which I took for as 'lower quality'. I turned stretching off for one raster and noticed it looks just about the same as its source, despite the minimum range value being different by +-1 in the imported one.

  4. #4
    Jeff Swain

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    Default Re: How to export lossless raster with same quality as source?

    There is a blog that talks about the stretching. I recommend taking a look at it and it can explain the effect.
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  5. #5
    Thomas Lupher
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    Default Re: How to export lossless raster with same quality as source?

    Thanks for the great info.

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