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I was prompted to raise this topic because I've just upgraded from terrestrial TV to Freesat with HD, and was rather surprised to find that there is very noticeable CA on the TV picture. So I thought I would seek opinions on the following:

 

1. Is CA purely a function of the lens or can it be introduced by other components in the chain?

 

2. When I finally get round to doing video, can software (e.g. Premiere Elements which I will most likely be using) remove CA in the same way that it can for still images?

 

3. Why do we go to so much trouble to remove CA from stills when it's so noticeably present in high-quality video imagery?

 

Alan

 

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I think digital TV is a double-edged sword, its great to have more channels and HD, but there are lots of quality issues that probably go unnoticed by joe public, that makes me think it ain't all that great. Quite often you'll see compression banding on "hd" pictures particularly in the corners of dark scenes (sunsets, candle lit rooms etc etc). I recently got a Sony Google TV box, and some of the HD content on there is way better than broadcast TV, normally when its been posted by a TV Channel.

 

On a separate note, how often do you noticed camera blegs/dust on screen, even on stuff thats been heavily manipulated, you'd have thought they would have taken them out.

Edited by York Photographer

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I suspect that because of the better resolution you are now just noticing what was always there.

Don't know about the software but if you think about it the problem is far, far more difficult. There are 25fps and the camera is not stationary. Ditto the dust.

The eye fills in a lot of gaps is moving images- it's the very basis of the art. Frame enlargements from 35mm. look awful, even at 10x8. You'd never believe such an image would suffice on a 50' screen.

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3. Why do we go to so much trouble to remove CA from stills when it's so noticeably present in high-quality video imagery?

 

Just on question 3, the automatic CA removal option in ACR 7 (Lightroom 4 included) is so effective that CA is a non-issue. When they removed the sliders I was a bit apprehensive as I'm always wary of automation and losing control but Adobe came up with the goods here for sure. No more messing about using sliders.

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Be very careful with the CA purple/green etc fringe removal. I have just finished a few shots of the Majorelle Gardens, which have a very strong Majorelle blue colour. I had to re-do several conversions as my default defringe setting (removes purple fringes) was creating a sharp, perfectly shaped, zero saturation (grey) halo round anything photographed against this intense blue!

 

David

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Be very careful with the CA purple/green etc fringe removal. I have just finished a few shots of the Majorelle Gardens, which have a very strong Majorelle blue colour. I had to re-do several conversions as my default defringe setting (removes purple fringes) was creating a sharp, perfectly shaped, zero saturation (grey) halo round anything photographed against this intense blue!

 

David

I have noticed this too but really haven't found a way of getting rid of the colour fringing without this result.  Can I ask how you did it David?

 

Pearl

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i should say I was referring only to the Removes Chromatic Aberration checkbox which removes lateral CA only and is very effective at doing so. Lateral CA is apparently most noticeable on wider angle lenses which is what I mostly use.

 

The Defringe sliders David is referring to are to correct for longitudinal CA which is apparently most noticeable on longer focal length lenses and is more difficult to correct for. I don't use it as I haven't needed to but there are a few pages on how to use it in Jeff Schewe's book "The Digital Negative" which provides all sorts of excellent info on raw processing with ACR and Lightroom for less than £20.

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Well, if you have a blue background, the fringing doesn't show... so I just turn off that (second panel) setting. It's off by default (set to zero). I turn the purple slider up to 10 for some lenses and conditions (mostly, my old classic 1990s film lenses which need this).

 

What may interest you is that I own both a Sony A900 and the new A99. Both are 24 megapixel full framers. I actualty bought back an A900 because I just can't do my studio work with the EVF, it's uncomfortable in a dimly lit environment with modelling lights. What I have found using my normal lenses is that the new camera has MUCH less CA and fringing. It is very clearly visible. So this is certainly not just a lens-related thing, and the profile for ACR must include the body. I was using an A900 profile since no profile for the A99 yet exists, and this may have added problems to my odd fringe situation.

 

David

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Thank you David.

I don't know why you were awarded a negative for that so I have given you a positive to counteract it. 

 

Pearl

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Thank you David.

I don't know why you were awarded a negative for that so I have given you a positive to counteract it. 

 

Pearl

Perhaps it was a slip of the mouse. If somebody purposely ticked a negative for David's post, it surely goes to show how silly these arrows are in a forum of this nature. If somebody didn't agree with what he said, then they should have replied, not ticked a negative.

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Drifting way off topic, but I may have inadvertently given David a negative tick on another thread, thinking that I was moving to the next page. Apologies, but I did correct the error! Similar box shape for both functions I believe. Not sure that there is a down arrow next page function at the end of each page, but there should be.

Edited by Bryan
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Someone else has mentioned this - navigating by swiping the screen of a tablet or smartphone results appears to be a culprit. 

 

Since these are "involuntary tic(k)s", perhaps we should call the phenomenon, "Alamy Tourettes".

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This has been raised before. Let's see what Alamy can do about it. My preference is that Alamy do away with the like/dislike buttons. We really don't need such juvenile features in our forum.

 

Ken

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As stated, the reputation marks are here to stay for now and an erroneous slip or purposeful vote now and again will not effect the grand scheme of things over time.

 

Any other off topic posts from this original thread will be removed from this point as it will be taking away from what would otherwise be a quite useful string of comments.

 

Thanks! 

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2. When I finally get round to doing video, can software (e.g. Premiere Elements which I will most likely be using) remove CA in the same way that it can for still images?

 

 

You can't remove CA from video like you can in pictures.  Sometimes you can help a little by adjusting certain colours/overall temperature, or you could try using a tool/plugin called chroma keyer, its included with Sony Vegas Pro and I guess other programs. When I've used it it has increased noise in the video and doesn't produce satisfactory results. I'm only using a prosumer camcorder so maybe with better equipment/software you can deal with/remove CA better.

 

The best way to prevent it is choosing the 'best' exposure, sometimes under exposing helps.

Edited by Vanwall Man
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