Creating a transparent image

[Ambrosia7177]

Hi. In the video forum @James Craner suggested creating a transparent image to help keep my slide the size I want when I insert a transparent slide with text into iMovie.

Even though he was a saint and did this for me, I would like to learn how to do it myself in Gimp.

Here is my best guess, but I would appreciate some guidance from the pros...


In Gimp 2.8, go to: File > New and choose...

Image size:
     Width: 1920 px
     Height: 1080 px

Advanced options:
     X resolution: 72 px
     Y resolution: 72 px

     Color space: RGB color
     Fill with: Transparency

Then File > Export As... "transparency.png"

Choose "Export"

Export Image as PNG

Interlacing (Adam7) __
Save background color ??
Save gamma __
Save layer effect __
Save resolution _X_
Save creation time _X_
Save comment _X_
Save color values from transparent pixels _X_

Compresson level: 9

Choose "Export"


How does that look?


(I'm not sure what to choose for: Save background color ??)

Thanks.

 

[chown33]

This is the kind of thing were I'd use my default strategy: Try it, see what happens.

Export it both ways, then test each image to see how it looks in use.

 

[organicCPU]

From the Gimp docs on exporting to PNG:

Save background color
If your image has many transparency levels, the Internet browsers that recognize only two levels, will use the background color of your Toolbox instead. Internet Explorer up to version 6 did not use this information.

I bet, for your use case, you could untick all checkboxes on export to save 82 bytes .

 

[Ambrosia7177]

From the Gimp docs on exporting to PNG:

I bet, for your use case, you could untick all checkboxes on export to save 82 bytes .

But do I uncheck "Save background color" like I asked above?

It seems confusing to choose...

Fill with: Transparency

...and then be asked...

Save background color _____

You know?

 

[organicCPU]

But do I uncheck "Save background color" like I asked above?

Yes, just uncheck it! It's not a mandatory, but it reduces the file size a bit and the background color is very likely an unnecessary information for any transparent slide in iMovie.

You could check it, if you had to put an image containing text surrounded by transparency on a web page with a specific background color. I.e., if a web page had a green background color like hex value #00ff00, one would choose the same hex value as the background color within the Gimp editor, right before exporting and then check "Save background color" in the export dialog. That could make the text appearing crispier on such a green background in certain (legacy) internet browsers. Gimp would add the information about the currently selected background color to the PNG as a piece of textual information in a part of the file (the bkGD chunk). Browsers that are only capable of displaying 2 transparency levels, instead of 256 levels, could use that piece of text to fill the areas of semi-transparent values, especially between the color of your text and the transparent areas, with the specified color value as a background. The idea was to provide a better transition between opaque and transparent pixels and less pixel clutter.
I don't think that iMovie cares about this information, but I guess that you're going to make A/B testing like @chown33 recommended and tell us your findings. Further, if I remember right, that PNG feature was an ancillary chunk, an additional optional setting, that has been declared as deprecated in the latest libPNG specs (a common software library to handle PNG files) so that this setting probably will disappear somewhen completely.

In other words, whether you fill a PNG with transparency and what background color you had chosen in Gimp while exporting a PNG are two completely different statements. Got it?

 

[Ambrosia7177]

@organicCPU,

Thanks!