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How to make one color transparent in a PNG?

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Marina
Marina on 1 Nov 2019
Answered: Walter Roberson on 4 Nov 2019
Hi, I am making maps and want to have the land transparent to then overlay over Google maps. The way around it I think is to creat the figure with land in black (as nothing else in the image is black) and the have that color made trasnaprent. I have not been able to do this so far... Here's the code, I appreciate anyone pointing me in the right direction. thanks
Screen Shot 2019-11-01 at 1.25.15 PM.png

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the cyclist
the cyclist on 1 Nov 2019
It's better to paste code than an image of code. Otherwise, if someone wants to try it out, they need to retype everything.
Marina
Marina on 1 Nov 2019
yes sorry,
fh=figure %('Menu','none','ToolBar','none ');
ah=axes('Units','Normalize','Position',[0 0 1 1])
axis(ah, 'square')
fh.Position(3) = fh.Position(4); %set width equal to height
m_proj('mercator','longitudes',[-96,-76.5],'latitud',[1,20]);
hold on
fig=m_contourf(long,lati,speed,V,'LineColor','none');
colormap(jet)
caxis([0 0.7])
fig = m_quiver(long,lati,outstrct.u(idx_lon,idx_lat),outstrct.v(idx_lon,idx_lat),8,'k','LineWidth',0.5);
m_gshhs_h('patch',[0 0 0]); % searches for the GSHHS database in /m_map/private. Sets land to black.
m_grid('box','off', 'LineStyle','none','xticklabels',[],'yticklabels',[],'xtick',[],'ytick',[]);
print('/Users/marinam_ar/Desktop/OPERATIONAL/MAPS_JEFF5_TRANSP/CURRENTS_Oct272019','-dpng','-r1200')

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Answers (2)

Sahithi Kanumarlapudi
Sahithi Kanumarlapudi on 4 Nov 2019
You can change the transparency of a color in an image using AlphaData property. The following link has an example
In order to change the transparency of an object on an axis you can use ‘alpha’ property. For more information refer to the following link
Hope this helps!

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Walter Roberson
Walter Roberson on 4 Nov 2019
print() to the png file. Then read in the file and write out a new copy of it that has the appropriate color set as transparent. See

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