PDA

View Full Version : Advanced P/S col correction



olddog
04-12-07, 12:15
In underwater photography we are routinely handicapped by radical blue /green colour casts. Most people try to fix the problem using basic functions like the auto correction tools in basic programs like microsoft photo editor. Big mistake! :confused:

You soon find out that auto correction in these programs very rarely works. In basic programs or even advanced editing programs the col shift in diving photog is well diverged from the parameters designed into auto tools logic.:(

Most diving photogs then progress into a decent editing program like Adobe. Things get better but it’s a black art and not an easy learning curve. Adobe is a tool and a half to learn and not user friendly. Combine this with the specific problems with radical col cast associated with diving and we se why many people don’t get far.

So some stick with it and master the basics like the levels tool in P.S. Closing up the sliders brings a lot of good results. Once leveled the auto fix can then stand a chance of working.

So you start to get to grips with the Adobe beast and an awful lot of picks still just don’t respond to the above levels technique. The simple reason is that in the physics of light absorption most of the red spectrum is missing at depth.

So now for some black art. Supplementing some of the missing spectrum of red using data from the other channels. We are technically moving from image enhancement to the black art of image manipulation.

How is it done? Well in the past I have kept quiet on how I achieved some of the photo enhancement results not because I didn’t want to share the methods, but because the methods were complex for me to explain and boring for those not big on U/W photog . But thankfully video says a thousand words easily. This link beautifully describes the basics of channel substitution and it's conveniently biased toward diving photog.


pFhrTQJg6MI

It may look complex but a lot of what is been done can be compiled into an action. An action is a repeatable set of complex instructions that can be applied to any image in P/S.

This is one of the more basic techniques available in the black P.S arts. I am away for a weeks hol but will teach a few more tricks from the olddog black box if any of you are interested.

regards Olddog

regthing
04-12-07, 14:29
Excellent article Olddog :D

Didn't know that myself!

(I've embedded the vid as well, hope you don't mind)

olddog
04-12-07, 15:10
One thing I should have mentioned is that serious photogs are divided into two groups. When deciding to cross over from enhancement to aggressive manipulation you cross a creative line.

Enhancing an image beyond simple sharpening and contrast adjustment will almost certainly bar a lot of shots from photog competitions. Personally I think the purists have got it wrong .Some of the guys who make the rules for competitions are dinosaurs from the film days. (Film ? it’s the quant old stuff you got from boots the chemist). These dynophotogs give me the hump. I have worked in the field of photographic development and most of what we do in the photo dev lab has analogies and equivalents in the digital lab.

My personal aim is to create as close as possible an accurate recount of what my eye sees underwater. How I achieve that is irrelevant.
Also I often use the pixels as a virtual pallet to create an art form that draws the observer's eye to what I want in an image.

So take yer pick creator or recorder Its up to you.

IanStevenson
04-12-07, 17:13
Another good one is to use noise correction processes on the R, G & B channels separately.

Generally R & G need a wee bit of smoothing (e.g. edge preserving smooth) but at higher ISO the red can be a disaster, especially if it has been amplified using manual white balance! There you can use a massive (e.g. 27) median filter to calm it down. That kills detail on the red, but since the detail on the other two channels is in-tact but most of the noise was on red, the re-composited image is MUCH better.

This is a good technique to use in conjunction with cross-channel blending above so you're mixing the "real" red signal with the other colour channels.

Ian

olddog
04-12-07, 17:35
Another good one is to use noise correction processes on the R, G & B channels separately.

Ian

Cheers Ian for that little gem. Now I think about it's so logical. Loads of times I agonised about noise verses sharpness. Hitting the isolated contributing channel is so obvious. Can you hear me kicking byself.

IanStevenson
04-12-07, 18:12
Cheers Ian for that little gem.

Does that mean that I have just succeeded in teaching olddog a new trick :D

PeterM
04-12-07, 22:48
I find the best technique is to post your basic image here and wait for olddog to fix it and then you can upload it back on to your pc the way it was meant to be! Magic! :D

olddog
05-12-07, 12:15
I find the best technique is to post your basic image here and wait for olddog to fix it and then you can upload it back on to your pc the way it was meant to be! Magic! :D

That’s cheating; :D you should try a bit photoshopery, it's reasonably easy once you get started. I can't resist dabbling in other peoples photos. But I am very hesitant to post results as I would hate to offend when not invited to work on the shots.

Perhaps U/W photogs who don’t have programs like P/S would like to post a few challenged shots that are worth working on. An invitation to work or improve the images would sharpen a few digital darkroom skills, and turn a few col cast shots into keepers. Of coarse not every shot can be saved but its amazing the power of programs like P.S.

Also as there are many methods of obtaining similar results its good to see how other digital editors weave their darkroom spells.

PeterM
05-12-07, 14:28
Please take this as an open invitation to tinker on my photos.

In the past I have done bits of touch ups on the odd photo, but I must admit that I simply don't have the time (or am not prepared to commit the time?) to tinkering with many of them - therefore I tend not to alter any unless it's for a specific purpose, like printing it off or for display or putting on one of those little electronic photo frames.

I had a wee look at you video, but my software doesn't do stuff that fancy - admittedly Chris has probably given me better software that I haven't installed!

Have fun!

olddog
05-12-07, 18:28
Please take this as an open invitation to tinker on my photos.
Have fun!

http://i60.photobucket.com/albums/h39/ranchuolddog/DiveLochFyneTripleReef17December200.jpg

http://i60.photobucket.com/albums/h39/ranchuolddog/DiveLochFyneTripleReef17December-1.jpg

Ok Peter better start on the jolly green giant av

P.S can I morf a dogs head on it! or how about a nice set of D. Pars on yer other photo

regthing
05-12-07, 19:17
http://i60.photobucket.com/albums/h39/ranchuolddog/DiveLochFyneTripleReef17December200.jpg

http://i60.photobucket.com/albums/h39/ranchuolddog/DiveLochFyneTripleReef17December-1.jpg

Ok Peter better start on the jolly green giant av

P.S can I morf a dogs head on it! or how about a nice set of D. Pars on yer other photo

:D :D

I've stuck this thread as I believe it is possibly the most important PS skill to master when tinkering with UW pics.

PeterM
05-12-07, 23:14
http://i60.photobucket.com/albums/h39/ranchuolddog/DiveLochFyneTripleReef17December200.jpg

http://i60.photobucket.com/albums/h39/ranchuolddog/DiveLochFyneTripleReef17December-1.jpg

Ok Peter better start on the jolly green giant av

P.S can I morf a dogs head on it! or how about a nice set of D. Pars on yer other photo

:D :D Some people are just too smart!

dive granny
05-12-07, 23:16
What does 'sticky' on a thread mean?

regthing
05-12-07, 23:23
What does 'sticky' on a thread mean?

If you go into a forum (e.g. Looking for a buddy? (http://www.congeralley.com/forum/forumdisplay.php?f=19)) the sticky threads always show up at the top no matter when they where posted. Handy for important or particularly interesting threads so that they don't get lost down the list as new threads are added. ;)

dive granny
05-12-07, 23:52
Thank you. That is clever:)

chris
06-12-07, 13:26
:D :D Some people are just too smart!

I had already done that to the original and gave it to you, you must just be too lazy to go look for it or lost it. I think Olddog will agree that it was arelatively easy one to do as the clarity is actually quite good for re-adjusting the RGB mix.