Bug 344810

When exporting a document with certain color space (CMYK or 16-bit) to a portable file format that doesn't support them (JPG/PNG), Krita returns a error message:

"Cannot export images in this colorspace or channel depth to PNG"

The problem is that the message is neither very informative nor instructive enough to many, especially new users. Many of them hit that message  because they would blindly choose CMYK at document creation, as if it is the more "professional" choice. They probably don't know what colorspace or channel depth are. They don't know JPG/PNG don't support CMYK or 16-bit by their specifications. When they see that error message, they would automatically blame Krita for not being able to export JPG/PNG. One of the laughable solution they told me was to use screenshot!

There can be 2 different solution I would like to suggest:
1. When exporting to JPG/PNG/GIF, automatically convert & output as RGB 8-bit without any user interaction, do not display any message;
2. Show the error message, but tell them to go Menu>>Image>>Convert... and Choose RGB 8-bit.

Personally I think plan 1 sounds better because it hides out all the rough edges, in Apple style.

Reproducible: Always

Steps to Reproduce:
1. Create a document with CMYK or 16-bit colorspace
2. Menu>>File>>Export>>to PNG

Actual Results:  
Krita returns a error message: "Cannot export images in this colorspace or channel depth to PNG"

Expected Results:  
Krita either automatically convert & output RGB 8-bit JPG/PNG file, OR, in the error message, tell the users to go Menu>>Image>>Convert... and Choose RGB 8-bit

I got many feedback like this from my DA, tumblr and other places. I guess this is one of the many reasons that people decided to uninstall Krita. I reported this because I got another one today! :b