It's interesting how things come together.
I can now use Icaros Viewer to make a Special App Icon that has three png images like my ShowPicture icon.
The next update for Icaros Viewer will include Resize To Fit and a method to blit a bitmap to a rasterport that is common to many Amiga like operating systems. It's the same method used by Magellan to display icon images.
I can also use INFO datatype to enumerate the images to export the third png image to be used in a fancy About Box for my programs. They will consist of a small 100x100 pixel image on the left and IntuiText to give a description about programs.
There's probably an easier way but I like a challenge.
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Here is the newest version of Icaros Viewer from this weekend. It can Save As, Save As PNG, Save PNG Icons. (See previous instructions).
In the next version I will add Resize To Fit, Use BltBitMapRastPort, and I may add Save As IFF to the menu to allow to save ILBM images.
Now that SaveAsDatatype is in place with all the supporting functions it is actually possible to save as any supported picture datatype. With that in mind I may change the menu slightly to File,Save,Save As,etc. such that Save will save a copy and Save As will allow adding your own file extension. For example, Save As... FILE.bmp, where FILE is the filename. The program will compare the file extension and if valid save using bmp datatype. Save As could be very useful.