Global Mapper v26.0

Batch Mode Export always Anti-Aliases

Matt
Matt Global Mapper UserTrusted User
edited December 2008 in Bug Report
I think this is a bug. It seems as though when you do a batch conversion GM will always apply anti-aliasing if you change the projection. To test, get a couple DRGs and batch convert them to a different projection. Then examine a line (roadway, elevation line, etc) and you will see that anti-aliasing was applied even when it was unchecked in options dialog.

It works fine when using a script to do the conversion. Only a problem when using the program to set options.

Matt

Comments

  • global_mapper
    global_mapper Administrator
    edited December 2008
    Matt,

    That is the current behavior, although it is by design. If you are reprojecting or resamping your export then anti-aliasing is always applied to avoid the small visible shift that typically occurs when pixel centers don't perfectly align and you use the nearest neighbor resampling mehod. To avoid confusing people and having folks always thinking that Global Mapper has a bug causing a shift when it is just a result of the resampling method used, anti-aliasing is applied automatically during batch conversion in those cases so that less savvy users get the expected result without having to do anything.

    Is the anti-aliasing causing a problem?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • Matt
    Matt Global Mapper User Trusted User
    edited December 2008
    Thanks for explanation, I had a feeling it might have been by design. I'm working a lot with USGS DRGs and the anti-aliasing tends to make them look blurry. I think because they are made up mostly of lines that are one pixel wide. The anti-aliasing turns each one-pixel wide line into a 3-pixel wide line and then they start to blend together. Also, just in general I prefer not to use anti-aliasing because it sometimes produces less accurate results than the visible shifting.

    Not a big deal for me since I can easily create scripts as a work around. But it is a little confusing since there is an option to enable/disable anti-aliasing and took me a little try and error to finally figure why sometimes it would anti-alias and sometimes not.

    Matt
  • global_mapper
    global_mapper Administrator
    edited December 2008
    Matt,

    I have updated the batch conversion to include a "never anti-alias" option so that you can disable the automatical anti-aliasing (interpolation) behavior if you need to. I have placed a new build at http://www.globalmapper.com/global_mapper10.zip with the change for you to try. Simply download that file and extract the contents into your existing v10.xx installation folder to give it a try.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • Matt
    Matt Global Mapper User Trusted User
    edited December 2008
    Thanks Mike. One other quick question. Do you automatically save image pyramids with GeoTIFF files? I noticed your GeoTIFFs with LZW compression are about 15-20% larger than the same file converted to TIFF with LZW compression by other programs.
  • global_mapper
    global_mapper Administrator
    edited December 2008
    Global Mapper does not save image pyramids in GeoTIFF files. I'm not sure why the LZW-compressed files would be larger than saved from other programs. Are the exact same settings being used like palette-based or 24-bit and the same pixel sizes?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • Matt
    Matt Global Mapper User Trusted User
    edited December 2008
    global_mapper wrote: »
    Global Mapper does not save image pyramids in GeoTIFF files. I'm not sure why the LZW-compressed files would be larger than saved from other programs. Are the exact same settings being used like palette-based or 24-bit and the same pixel sizes?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com

    I've been using 256 color GeoTIFFs. Photoshop and ACDSEE both save the files about 20% smaller with same exact settings. Even checked the color tables for your version vs. their versions, exactly the same.

    Attached is example. Just open this with GM, export as 256 color GeoTiff with LZW compression and it will go from 4.8 MB to 5.9 MB.
  • global_mapper
    global_mapper Administrator
    edited December 2008
    I took a look at the differences and found that the Photoshop-generated file saved the entire contents of the file in a single strip, which is specifically recommended against by the TIFF standard committee, although it does result in optimal LZW compression. I was able to significantly improve what Global Mapper does without going to the undesirable extent that Photoshop does and get comparable compression. I have placed a new build at http://www.globalmapper.com/global_mapper10.zip with the change for you to try. Simply download that file and extract the contents into your existing v10.xx installation folder to give it a try.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • Matt
    Matt Global Mapper User Trusted User
    edited December 2008
    Works great. Files much smaller. Thanks. I'll leave you alone for a while now :)

    Matt

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