If I made an advertisement for printing in CMYK mode but I need to upload that file as JPEG online for client, should I use RGB?
Files for professional printing should be CMYK.
Most desktop printers are calibrated to print in sRGB color space not CMYK though.
If you are making a file for the web you should convert it to sRGB not just RGB. if you leave that up to the browsers you will get a poor color conversion see photo.
Well the issue with this workflow is that the colors will not match. Ideally if you are wanting to show a print job it should be printed. That said I hope when you send a proof you are using a disclaimer and educating the client that if they are not calibrated, colors you send them may look differently.
Also, I would send it to them in CMYK and suggest they print it. Signing off on a proof online is incorrect and will lead to possible issues when it goes to print.
You should not send a proof in a
.jpg file but rather than in a
Yes, anything that is intended to display online should be in RGB. The web display standard is sRGB specifically and anything for display on the web should be converted to sRGB using "Perceptual" or "Relative Colorimetric" as the rendering intent. Evan's example shows very well what happens if an image isn't converted before being placed online. Although he's referencing Adobe RGB, the same applies to any color profile or color model, such as CMYK, that isn't sRGB.
Once it's converted, you don't need to include the color profile if the image will only be displayed online. All browsers assume an image is sRGB (one reason you're not likely to have much joy with a CMYK jpeg) and will display it as such.