First up a disclaimer.
This won’t be updated much or a regular series as not much is known about the graphics functions in UIFlow. However, the following steps is how I get images on to the M5Stack using UIFlow.
OK here is what worked for me.
Download and install G.I.M.P G.I.M.P.org
create a file 80x160px (for M5Stick) ,
Add graphics,
Goto Image>mode>Indexed,
Make sure ONLY “use web optimised palette” and “Remove unused and duplicate colours from palette”.
Goto File>Export As,
save the file as .jpg (filename must only have 7 letters),
Set “Quality” to 90% you may have to reduce this depending on image.
Click on ALL the boxes to remove the X
Click on advanced,
Unselect everything by clicking on the X to remove them,
Set smoothing to 0,
Set Subsampling to 4.2.0
Set DCT to integra and hit save.
Open UIFlow,
Click on the manager icon to upload the image to the M5Stick C,
Drag an image element to the screen and click on it to set the image to the one you uploaded, and then click the > “Play” icon to check the image.
If this helps you, please let me know.