Problem exporting still frame - color noise (vertical banding)

[grownupboy]

hey all,

been working in final cut for years (since version 2!) so i'm sort of well versed in many aspects of its use. i do however have a problem for which i can't seem to find a solution.

currently using a sony nx5 and transcoding to prores on capture. no problems there. i develop for the web so my final output is always digital.

i keep everything yuv until final output which is typically h.264 - resizing scenes using uncompressed 8 bit 4:2:2 then send the uncompressed clips to squeeze for compression.

i must create a series of still frames as part of my workflow. naturally i do this by meticulously stepping through the sequence and hitting Shift+N when i want a still. I drag the still to a new bin then when then drag all the stills i created to a new timeline that matches the settings of the timeline that i took the stills from (again uncompressed 8 bit).

everything looks fine until i export the timeline as an image sequence using quicktime conversion. i export as image sequence and generally use png as the output format although i've tried psd and pict files with the same results.

the problem:

before the export to stills the images look fine. after export they all have a strange color distortion with vertical banding between contrasting colors. again, this effect is NOT there prior to export as still sequence and the colors look fine.

here's the movie prior to exporting a still:

http://farm5.static.flickr.com/4062/...d486d8f4_o.jpg

^ (this is a screen grab of the actual movie playing in the quicktime player)

and a still image taken from the same frame of the movie using export as quicktime conversion (png):

http://farm5.static.flickr.com/4024/...ab63515b_o.jpg

note the lettering on his chest when you compare both images - there is a strong vertical banding surrounding the orange letters against the blue tshirt in the still image that is not present in the screen cap of the actual movie.

the same thing happens if i export the frame at the current playhead position as a still image using quicktime conversion. basically, anytime i export from final cut as a still (no matter the file format or technique used) i see the issue. even tried exporting image sequence using compressor.

i realize that 4:2:2 isn't the best color space to work in but this vertical banding between contrasting colors is not present in the original movie - only in the still image that is exported from the original movie. there is no compression added to the still image, and i have tried all formats available.

anyone else experience this? have a workaround? i've been using final cut for a while but this kind of has me baffled!

thanks for your help!

karl

[NoahKadner]

Just use the screen grab- they are identical in terms of the level of possible image quality you could expect from a still image off video.

Noah

[grownupboy]

hi noah,

unfortunately this is not possible as i need to generate up to 500 screen grabs per scene. i need a workflow that is reasonable and managable.

also - looks like flickr sized down the image and minimized the problem in doing so - re-added seperate images so you can really see the difference in quality.

karl

[TomWolsky]

That's as good as you're going to get on resampled images to adjust for aspect ratio.

[csharp]

You are sampling your stills from a 8-bit uncompressed sequence setting.

Change your sequence settings to a higher quality. Try "10-bit uncompressed", or even "none". Since this will undo any rendering it would be a good idea to duplicate your sequence first as a back-up.

Note the time-codes of the still frame locations in the sequence first to avoid navigating unrendered video.

See if that helps.