DPC Mentorship - Exposure Part II

Nikon AF-S NIKKOR 24-70mm f/2.8G ED

10/20/2005 10:57:43 AM · #101

I'll extend it through Sunday, then.

Dr.Confuser

Nikon D800

10/21/2005 05:56:24 AM · #102

Greetings from Lhasa Tibet. I took a quick peek at DPC and this thread from an internet cafe here. It looks like Zed's doing a fine job and as are you all. Keep up the good work and I'll be back in a about a week!

10/23/2005 06:12:04 PM · #103

*nudge*

If you folks haven't been outdoors taking pictures this weekend, yet, now's a good time before it gets totally dark.

Sony 24-70mm F4 Vario-Tessar T* FE OSS

10/24/2005 06:23:38 PM · #104

*cough* Hello? Anyone out there? The entire weekend came and went without anyone else responding. I'd think that a week and a half should be enough time to take a couple photographs...

Bear_Music

Samsung Galaxy S24 Ultra

10/24/2005 09:27:38 PM · #105

Everyone's laying low on my two mentorships also. Must be the weather or something...

R.

10/25/2005 10:59:22 AM · #106

Thanks for letting me know. It might be tests. We're coming up into midterm territory for college students. I kind of wish someone would at least check in, though.

10/30/2005 06:29:38 PM · #107

Another weekend is rolling by. Armelle, are you still out there? Sheapod, would you want me to move on if everyone else seems to have vanished?

(Argh. DQ is going to kill me for scaring off 99% of his group.)

sheapod

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

10/30/2005 07:00:39 PM · #108

Zed,
If you're ready to move on then I'm ready to continue. If you'd rather wait a few more days to see if the rest of the group rejoins us then that's okay as well. I'll just keep checking back.
BTW, thanks for the tip on using bracketing in continuous mode. It worked great when I tried it with the drive mode on the right setting. Amazing how that works. lol
-Laura

David.C

Nikon AF Nikkor 50mm f/1.8D

10/30/2005 07:09:19 PM · #109

I read the thread when I can -- but mandatory overtime doesn't leave much free time. I like the extra money, not having any time is getting old and the projects are piling up.

But, even if I had the time right now, my camera doesn't write RAW files so I would be sitting this segment out anyway.

David

11/03/2005 10:25:04 AM · #110

Sorry! Haven't had much time to take photos lately but I'm back in the thread now :) Zed, you've been great and full of amazing info. Thanks!!
Armelle

11/03/2005 10:42:43 AM · #111

Yay! At least one other person left. How much more time would you need, Armelle?

11/07/2005 10:55:43 PM · #112

Sorry, just flew back from a trip last night ... Good to go now :)

11/08/2005 12:53:23 AM · #113

Nifty! Two live people is a figure I can work with. Any chance you can get your "expose to the right" exercise in by Friday?

11/08/2005 10:25:42 PM · #114

sure!
Armelle

11/12/2005 11:55:09 AM · #115

Here are some of the photos I took for the mentorship. All are at ISO 400 and all are overexposed by a successive one third stop.

The one at 2500 has just the tiniest of clipping (and a minuscule blinking sliver) but no information in the 'fifth' quadrant of the histogram.

The one at 1600 has a bit of clipping and the histogram curve just enters the 'fifth' quadrant.

The one at 1000 has some clipping (and almost a third of the egg 'blinking') but also with a histogram that has a lot of info in the 'fifth' quadrant.

at 2500

at 1600

at 1000

I have to say that as a novice photographer, I never really paid much attention to the histogram WHILE shooting photos. But now I know that I should view the photo plus its info simultaneously and see both 'blinking' exposure areas and clipping to better judge exposure!

Thanks for pointing that out!! It really does pay off to do the homework :)

Hope I did this right??? I'll try to see if I can add the histograms later... not sure how to copy them...
Armelle

11/13/2005 05:29:18 PM · #116

Nice work, Armelle... you've managed to demonstrate where this technique breaks down. :P

What you shot was a scene with large dynamic range -- going from deep shadow on the left to pure white light reflection on the right side of the egg. Exposing to the right works best in the opposite case, where the lighting is more even.

You did strike upon the importance of checking your histogram when setting up shots in a new lighting environment, however. If you were already seeing the clipping indicator at in the 2500 image (I assume that means 1/2500sec), then that was your immediate indicator that it was unsafe to go higher (in this case, the 1/2500s shot doesn't seem to actually be clipped; the warning indicator will start flashing just before you hit the edge).

I am a little confused about one thing, though: what mode were you shooting in? If your aperture was constant, going from 1/2500s to 1/1600s is a 2/3 stop increase in light, not 1/3 stop. Likewise from 1/1600s to 1/1000s is another 2/3 stop... for a total of 1 and a third stops overexposed in that final image! That's about guaranteed to blow even the flattest lighting.

I'll post the next assignment tomorrow, I hope. I started posting what I had written on using the Exposure Compensation and Brightness sliders in ACR against each other to unclip highlights, and then suddenly realized that neither of you is using Photoshop CS (you'd think I'd have noticed while I was writing it, bleh), so it would probably be completely useless to you. Now I'm writing up something on unclipping highlights and recovering detail via single-channel B&W conversion, but that's going to take me a little longer. Please bear with me.

Canon EF-S 55-250mm f/4-5.6 IS

11/19/2005 03:44:22 AM · #117

Sorry for the delay folks, but I think I finally have something for you...

This is an "anyone-can-play" edition of the RAW Exposure Mentorship -- which is to say that although this technique works better when starting from RAW and in 16-bit mode, you can still try this out in 8-bit mode from JPG and it may still work out reasonably well.

Getting a Channel Mixer if you don't have one:

One of the things that delayed me was that halfway through I discovered that the tool I was using while writing (the Channel Mixer) isn't available in Photoshop Elements... or at least, it isn't normally. I have since found a solution.

Those using Photoshop Elements should head over to Earthbound Light and follow the instructions there to insert the Curves, Channel Mixer, and Selective Color tools back into the Photoshop Elements Effects list. (We'll only be using the Channel Mixer for this exercise, but the other two, particularly Selective Color, are also immensely useful, and I encourage you to play around with them.)

Recovering Detail By Discarding Information:

In previous exercises, I had pointed out a particular kind of blown highlight: the type where only a single color channel is blown. It's a notably dangerous kind because unless the channel that is blowing is green, it often won't set off the blown highlight indicator on the camera or be immediately visible in the histogram, leaving you with no clue that you've just lost detail and posterized until you're back at the computer and can no longer reshoot.

Sometimes, when feature detail is more important than color, however, this can be fixed -- by using only the information in the channels that didn't blow.

The technique:

For starters, you have to know *which* channel blew. For this, open up the histogram, and make sure that it shows you the histogram for each of the red, green, and blue channels.

Sheapod gets a free pass here because one of her previously posted images works out well as an example (her corrected-raw-over-1600 shot):

The black part shows you overall luminance, and should be similar to what you'd see from the histogram on the back of the camera. The red, green, and blue areas show you that the red channel is badly blown (pressed up hard against the right hand side), but the green and blue channels aren't too bad off.

So what we need to do here, if we want to recover some detail in the blown areas, is throw away the red channel. This is going to make the colors look awfully screwy, so the best way to deal with it is to discard color completely, and work on a black and white conversion.

Normally, if you just desaturate an image to create a black and white version, it won't change the overall detail or light balance; light spots will remain light, and dark spots will remain dark. We're going to use a special technique of desaturating by using just the information from one color channel instead.

Start by creating a Channel Mixer adjustment layer. Normally, as you look through each channel, the Red channel gets 100% of its values from the reds in the image, the Green channel gets 100% of its values from the greens in the image, and the Blue channel gets 100% of its values from the blues in the image. (This is something of an oversimplification of how the Channel Mixer works, and in fact there are techniques involving numbers of > 100% or < 0% of each portion, but I'm not going to get into that here.)

Since we know the red channel is bad, we're going to want to work with one of the other two, or even both, and compare. If you want to use just the Blue information, for instance, what you'll want to do is set the Red channel to be 100% blue (and 0% red and green), and the Green channel to be 100% blue (and 0% red and green), and the Blue channel to be 100% blue (and 0% red and green, which is how it should be by default anyway).

Congratulations, you should now have a black and white image that looks better than a standard desaturation. It may not be the best possible image, however -- try using the other color channel to see if that works out better (e.g. set each channel to be 100% of the green source instead). The nice thing about layers is that you can put up a couple of them, switch off the visibility of the one you don't want to see, then quickly switch back and forth to see which one works out better.

You may also want to a little of each of the good channels to fix a blown channel. Instead of using 100% green and 0% blue in each channel, for instance, try 50% green and 50% blue.

Bonus color technique: sometimes you can get striking effects by not changing all the channels. For instance, set the Red channel to 50% green, 50% blue, the Green channel to 50% green, 50% blue, but the Blue channel to 100% blue, or some similar combination.

Assignment:

Find one of your images that has a single blown color channel (the histogram should look somewhat like the example I posted, with only one or at most two channels pushed up against the right hand side, with at least one channel okay). Sheapod has an advantage here in that I've already pointed out an image that she has previously posted that would work, though of course I'll be just as happy if another example is chosen.

Take this image and crop down to a maximum 640x640 region around one of the areas with a blown channel, so the affected area is easier to see, and we don't have to deal with resizing issues.

Post the following images:

1) The original image, cropped to show the blown color channel
2) That image, with just a Hue/Saturation layer used to completely desaturate the image.
3) A black and white conversion using the Channel Mixer. Post which channel (or channels) you used, in what amounts, and why (e.g. blue made a portion of the image too dark for your taste, so you went with green, or blue brought out more detail in the blown area, so you went with that, or the hybrid looked better to you overall, or whatever the reason was).

Extra credit:

4) A version of the image where the channel mixer settings were asymmetrical (i.e. there will be some color left in the image, but not the way it used to be).

Feel free to make a final light sharpening pass or a slight levels adjustment before posting, but please don't tinker with the other tools and keep the final touches subtle; I'd like this to just be an exercise in this one technique without too many distractions.

I'm going to be out of town for the rest of the month, which gives you two weekends to come up with and process an image. I would very much like to see the assignments posted by the time I get back. It's two full weekends, after all. :)

Message edited by author 2005-11-19 03:45:07.

tolovemoon

Canon EOS Rebel SL1

11/21/2005 11:44:45 AM · #118

Hey Zed, I must admit I feel bad for the absence and I do apologize for the lack of communications...
I had to take a break from a lot of things that occupy my time so much specially the things that make me a procrastinator....I am back at it though and I am going to study what I have missed here ...
I will also submit assignments and get back to commenting...
Just bare with me a little, as my schedule is pretty full though with 15 minutes planned at 4 different times in one day. As long as I keep it up the intire week maybe I will learn something and possibly submit a blue ribbon photo :) In any case I just feel very appreciative and thankful for all the efforts that you and everyone here puts into helping each other learn new things as well as the patience or understanding for some that are always late (like me) :)

11/28/2005 07:32:33 PM · #119

*cough*

So, I finally make it back into the country, and nobody has posted a photo yet?

*sniff* Nobody loves me.

(For tolovemoon or anyone else who missed submitting for an earlier segment, it's not too late, and I'll happily help out anyone who wants to go back and work on an earlier technique.)

Nikon AF-S NIKKOR 24-70mm f/2.8G ED

12/01/2005 10:11:53 AM · #120

Hey Zed,

I haven't even submitted to challenges the last few weeks for lack of time... But I've learned a lot from you and will try to follow along and do my HW! I'll have time to shoot this weekend, hopefully :)
Armelle

Dr.Confuser

Nikon D800

12/09/2005 01:42:38 AM · #121

I am so sorry!

When I returned from China & Tibet, I had hoped to pick up from Zed and continue this mentorship thread. While in China I developed a new Zen consciousness and can no longer lead this thread. (Actually, that is not true. I have a life outside DPC which includes Board relationships w/ 2 universities, a dynamite messaging start-up in the Seattle area, and a venture capital firm in Silicon Valley (USA)). These have taken more time than planned and Zed will need to take over the thread.

Maybe after the first of the year, I will post 150 of 2,064 China/Tibet photos and you'll see wehat I mean about overload.

In the mean time, please PM Zed about his willingness to continue! And think about your personal commitment. In the words of of Yoda, "Do or do not, there is no try."