This is a spin off from the tutorial by Stygg on Surreal Backgrounds.

I decided to try to create a sky, without clouds, figuring I could add in clouds as needed and to use the sky as a standard sky backdrop.

So, I tried 3 variations.

1) BLEND - a light sky blue bottom rectangle strip and a deep sky blue top rectangle strip. I blended using 50 steps. Sky looked great! Then I exported at 300dpi for printing in JPG and again as PNG

2) TRANSPARENCY - a light blue rectangle, with a dark sky blue rectangle on top using a linear transparency. Sky looked great! The I exported at 300dpi for printing in JPG and again as PNG

3) BITMAP TRACER - I used the bitmap tracer to trace my original photo. I set at 20 passes, remove noise to 50, color tolerance set to 0, and accuracy set to 100. Sky didn't look great as there was two jagged white lines across the sky. Then I exported at 300dpi for printing in JPG and again as PNG

Then, I sent the electronic files to Don's Photo and had a 4 x 6 printout of each variation.

Unfortunately, none of them were acceptable.

The bitmap tracer photo had very obvious color sections (both JPG and PNG)
The blend photo had very obvious horizontal color lines (both JPG and PNG)
The transparency photo also had very obvious horizontal color lines (both JPG and PNG)

Any ideas on how to create the sky so these horizontal lines don't show up in the printing?

Very disappointing that the transparency and the blend looked so good on the computer screen, but did not print out well.