What happens if you use the PNG codec instead of the Photo-JPEG codec?
I think the lines are gone but I'm not too sure, because the video really lags and it plays only every 5 seconds. The frame is constantly stucked in between.
Please help me out, thanks a lot in advance.
The reason it is lagging like that is the data rate of the video is too high for your hard drive to handle.
The reason those lines show up in the Photo-JPEG file is that the Photo-JPEG codec is a lossy codec. It compresses things so you will see some quality loss in certain areas. The subtle gradation of the sky is, unfortunately, an area where you will see compression artifacts.
I would suggest the lagarith codec, DNxHD codec (free from Avid), or the Cineform codec (free from GoPro) as your intermediate codec. The data rate will be lower than the PNG codec and it will hopefully be less compressed than the Photo-JPEG codec.
A couple of questions for you. First are you resizing the output in the output module? If so, don't do that, the scaling algorithm the output module uses is IMHO horrible.
Second, what are the quality settings on your photo JPEG? If they are not 95% or better you're probably just seeing compression artifacts.
For best results with the minimum noise I would create a new 1080 P composition, drag the 4K footage into that comp, resize to fit horizontally, then apply unsharp mask and/or filters to reduce the amount of noise and add some detail to the footage. The project would be set the 32-bit and I would render not to photo JPEG but to JPEG 2000 or PNG QuickTime. In both cases quality would be set to 90% or better.
A faster option would be to use the Adobe Media Encoder. Bring your 4K footage into the AME use a 1080 P preset and render to JPEG 2000. Manually scale down the footage so that it fills the frame and does not distort. I have found that the Adobe Media Encoder has better scaling algorithms than the output module when scaling down footage.
I need the photo-JPEG codec because it is a requirement from istockphoto website when submitting footage. I don't think they accept JPEG 2000 as shown on this page: Stock Photography: Search Royalty Free Images & Photos - iStock
I've also tried the 1080p composition and dragging 4k footage in and scale it down, then apply and render everything at best setting, still the same problem, even when using the Adobe Media encoder as well.
There must be some noise in your 4K footage. If you can post about 60 frames of a clip in native 4K I'll give it a try.
By the way, you resized your screenshots so we can't see any problem with them. Scaled down screenshots are basically useless. The forum will accept full frame images, they are just scaled when embedded by html codes.