transparent color

djameldjamel Global Mapper UserPosts: 9
Good afternoon
when i try to choose a transparent color  for a raster layer I dont have the box with the title : " transparent color"
 and when I choose a color from the color palet I D'ONT HAVE A RESULT. Any help please ; I 'm using GM v 17.1 thanks.

Answers

  • bmg_bobbmg_bob Global Mapper Programmer Posts: 2,026
    Hello,

    What version of Global Mapper are you using?  What is your workflow when you choose a transparent color, i.e., what steps are you performing in Global Mapper?

    Cheers,

    Bob
  • djameldjamel Global Mapper User Posts: 9
    Good Morning

    I'm using GM V17.1. After opening a raster I have done these steps:
    control center , option ,display tab , transparency , set transparent color ,I choose a color (indicate RGB values) , apply ,no result
    thank you for your help.
  • bmg_bobbmg_bob Global Mapper Programmer Posts: 2,026
    djamel said:
    I'm using GM V17.1. After opening a raster I have done these steps:
    control center , option ,display tab , transparency , set transparent color ,I choose a color (indicate RGB values) , apply ,no result
    thank you for your help.
    Thank you for the information.

    Unfortunately, we don't currently have a way to pick the RGB values from the image.  There is an open feature request to be able to do that, but it hasn't been implemented yet.  In the meantime, if you know the RGB values you want to use, you can type them into the Color dialog, as you are doing.  Then, on the Display window, move the slider under "How Similar Must Colors be to Make Transparent?".  If you move the slider towards "Fuzzy", you will get more pixels marked as transparent.

    If you are not sure what RGB values to use, choose the Feature Information tool and click on your raster image.  The Pixel Information screen will be displayed with RGB info about the pixel you have clicked on.  

    Cheers,

    Bob
  • Ice Age MarkIce Age Mark Global Mapper User Posts: 299Trusted User
    I think I might be the person that originally suggested/requested that the transparency function for colors have a slider, instead of a fixed, built-in default value.  I was trying to clean-up some lossy .jpg imagery with a lot of noise.

    If I remember, the old default value was 17, so it's possible that you may have to get at least that 'fuzzy' to start seeing an effect, rather than at 0.  Some imagery (like .jpg) has so many different RGB colors that picking one of them for transparency from what seems to be a single color to the eye may not have the desired effect.  Getting more 'fuzzy' can help, but almost always, pixels then start dropping out of areas that you don't want to be transparent.  Trying to make water transparent this way on satellite or aerial imagery is a classic example.  It seems to all be a similar color, but it's not really, and the land areas will have similar pixels that will start disappearing.  Only a mask, or crop will work well.

    Sometimes you can use another program (like free Irfanview), to change several/many different pixel colors to the same single RGB value, and achieve some additional transparency effect in that way. 

    With pallete based imagery, you can choose more than one color to make transparent by using 'Control' or 'Shift' to multiple select.  With non-pallete imagery you can also make multiple colors transparent, but only by using a simple script.  In the script, you can specify more than one RGB combination for your transparency color.  They will all have the same 'fuzziness' though; i.e. you can't specify that seperately.

    Hope those couple of tidbits might help anyone using this feature in GM.

    Mark  
  • djameldjamel Global Mapper User Posts: 9
     it works now , thanks
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