Red/Pink line ?

[Robin Probyn]

Hi there

Bit of an odd question but..

Shot a test HDX900 1080i/25p half-shutter Nano 50mbs MOV. lastest firmware..
A white lamp shade.. against white silk curtain,.. was giving me a red/pink line along the shade edge..against the white curtain..

Everything else fine..

Viewing on Mac book.. Not pro.. Quicktime..

Any idea,s ?

Thanks

[Mark Job]

Hi Robin:
There are sooo many things which could be coloring the image you are seeing on your MAC laptop that it's sad. Do you own, or have access to an HD monitor ? Check playback on one of those first, then you will know for sure if something is amiss.

[Robin Probyn]

Hi Mark

Thanks for your time.. yes not so apparent on HD monitor.. Pana 900A .. see it much more on Mac book

Re shot just now .. same scene.. and seemed to have gone away.. the curtains have a very fine grain pattern in the material.. I think it depends on the folds.. some sort of optical thing I think.. ??

Thanks again

[Dan Keaton]

Dear Robyn,

"Red/Pink" may be magenta, and it may be chromatic aberration.

Is there a slight green line on the other side of the shade?

Is the "Red/Pink" line towards the edge of the image as opposed to the center?

Which lens are you using?

If you have a good HD-SDI or HDMI monitor, is the "Red/Pink" line visible when playing back the footage directly from the nanoFlash?

[Robin Probyn]

Hi Dan

Yes I would say magenta.. other side of shade is against a green curtain ! so not sure about that.. :)

And yes the line is right on the edge of the shade..

Yes good glass.. HD Fujinon.. 4.5 wide angle zoom.. much less pronounced on Pana HD 900A on play back from Nano.. but still there a tiny bit..

Iam sure its to do with the very fine grain in the curtain material ..chromatic aberration.. what causes it to be magenta?

Thanks for your time.. again !

[Dan Keaton]

Dear Robyn,

Technically it may not be chromatic aberration.

With certain cameras, under some contidtion, when going from one color to another, there is sometime a green line on the left and a magenta line on the right.

Are you recording at 50 Mbps or above, thus 4:2:2?

[Robin Probyn]

Hi Dan

Looks like lateral aberration .. from a quick look on the net.. edge against a very bright background.. actually magenta strip was on the left of the shade.. not an aperture settings or even a shot I think I would ever do on a real shoot.

Shooting 50Mbs Long GOP MOV.. had the lens a while and no complaints under many different circumstances .. but nearly all of that,99% has been shooting DVCpro HD.. not with the nano.. so in theory 100Mbs.. maybe just something to watch for with that lens?

[Dan Keaton]

Dear Robyn,

If you can recreate the shot, please do so while recording to tape also.

When you run the tests, record some at both 50 Mbps and 100 Mbps Long-GOP.

I assume that you recorded the scene originally in 1080i50.

The DVCPro HD is far less resolution than the nanoFlash.

DVCPro HD reduces the resolution before compression, the nanoFlash does not.

nanoFlash
1280 x 720 for 720p
1920 x 1080 for 1080

DVCPro HD
960 x 720 pixels for 720p,
1280 x 1080 for 1080/59.94
1440 x 1080 for 1080/50i

(Specifications for DVCPro are from Wikipedia)

DVCPro HD may be 100 Mbps at certain frame rates, but drops down dramatically at other frame rates, such as 24p. The nanoFlash always gives you the requested bit-rate regardless of the frame rate.

[Robin Probyn]

Hi Dan

Ah ok interesting.. what Mbps does DVCpro go down to at 25p...? so would higher resolution give more chromatic lateral aberration ? or no effect?

Thanks again!

[Dan Keaton]

Dear Roby,

Wikipedia sates that at 24 frames per second DVCPro goes down to 40 Mbps.
It does not state the bit rate at 25 frames per second.

We do not know if this is chromatic aberration or not.

A carefully controlled test, with your camera, your lens, running both tape and the nanoFlash at various bit rates would be very desirable.

Remember, the nanoFlash is just more faithfully recording the images from the camera.

[Robin Probyn]

Hi Dan

Interesting I didnt know that the 100mbps fell to 40 at 24p.. presumably 25p isnt much more..

So shooting at 25p with the nano at 50mbps is actually a higher bit rate than going to tape..???

Looks to be purple fringing.. thing.. cant think what else it is.. but yes could shoot some more tests.. as long as I have the curtains and the sun still shines :)

Thanks again

[Dan Keaton]

Dear Robyn,

The difference is far greater than the 10 Mbps between 40 Mbps and 50 Mbps.

First, the nanoFlash records the full resolution provided to us.

Second, the nanoFlash, at 50 Mbps, is Long-GOP, and much more efficient than I-Frame Only at these bit-rates.

Good luck in your tests.

I highly recommend that, if you do the tests, example the images carefully on a good monitor, before or while you are recording. If you can see the fringing, the nanoFlash will record it.

[Lance Librandi]

Hello Dan,
While you on the subject of Long Gop Vs I-Frame do you have a comparison chart that you could post for the various bit rates.

Many thanks

[Mark Job]

Originally Posted by Dan Keaton

Dear Robyn,
nanoFlash
1280 x 720 for 720p
1920 x 1080 for 1080

DVCPro HD
960 x 720 pixels for 720p,
1280 x 1080 for 1080/59.94
1440 x 1080 for 1080/50i

(Specifications for DVCPro are from Wikipedia)

DVCPro HD may be 100 Mbps at certain frame rates, but drops down dramatically at other frame rates, such as 24p. The nanoFlash always gives you the requested bit-rate regardless of the frame rate.

...Hey Dan: Oh crap ! I didn't know that ! I assume this is also an accurate statement covering the Flash XDR ? 1280 x 1080 = 1080/59.94i = SUCKS ! Less pixels at *any* data rate is still less pixels.

[Dan Keaton]

Dear Mark,

Sorry, but I do not understand your comments.

The Flash XDR and nanoFlash always records full raster.

Full Raster for 720p = 1280 x 720 (1280 horizontal pixels, 720 vertical pixels).

Full Raster for 1080 = 1920 x 1080

The DVCPro HD is the codec that throws away resolution, then encodes the video stream.

The nanoFlash does not throw away any resolution.