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DPChallenge Forums >> Tips, Tricks, and Q&A >> Correcting Exposur with Gray Card
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 08/10/2006 11:16:30 PM · #1
Any thoughts on how this can be done with PS CS2.

I can balance the colour with the gray card in the shot but am having some trouble getting the exposure right.

Can the exposure be corrected or adjusted to be more right with the gray card? If so, can someone steps be posted here to this thread?

Thanks in advance!
Peace
Rooster
 08/10/2006 11:44:10 PM · #2
Originally posted by Rooster:
Can the exposure be corrected or adjusted to be more right with the gray card? If so, can someone steps be posted here to this thread?

I think it can but you need to have the Grey card with Black/Grey/White portions.
 08/11/2006 12:09:10 AM · #3
You just use levels or curves and select the bright droplet, click the white box...pick the dark droplet, click the black box. select the mid-tone droplet, pick the mid-tone.
 08/11/2006 12:29:24 AM · #4
I would really recommend one of the new calibration targets with white, gray, and black stripes.

The kodak gray card reflects 18% of the light that hits it, but it's not necessarily color balanced. The newer targets are 18% gray and color balanced to you can use them to set your white balance as well. And, as deapee pointed out, you can use the three bands in your levels and curves adjustments.
 08/11/2006 12:36:41 AM · #5
Originally posted by deapee:
You just use levels or curves and select the bright droplet, click the white box...pick the dark droplet, click the black box. select the mid-tone droplet, pick the mid-tone.


I think most PS users manually move the levels and curves and don't realize the eye droppers can be used to select the hi, low an dmid points very accurately. The mid point is the most difficult but you ncan use layers to adjust and find the exact mid level gray too. I normally set the hi and low and guess at the mid. Try using the eye droppers, they work great.
 08/11/2006 12:36:55 AM · #6
Yeah, this blows. I went to B&H today & asked if they had the tri-shade cards & this one grumpy old dude looked at me as if I was crazy, saying that there was no such things as a black card. Whatever.

The tri-shade card was what I really wanted but seem to remember reading that the exposure could also be corrected just using the gray card which is all that I used to shoot some artwork today.

Any thoughts on if & how the exposure can be 'perfected' using just the gray card?

Also, where can I get a good but cheap tri-shade card with black/gray/white on it? The kodak color chart was 40 effing dollars at B&H! It's a piece of plastic with colours on it man! What gives!

Thanks in advance!
Peace!
 08/11/2006 01:47:02 AM · #7
A trick to find the grey point
Someone showed me this technique and I put it in a thread, it is really useful for correcting white balance but doesn't correct the exposure.
 08/11/2006 12:40:50 PM · #8
Originally posted by Rooster:

Also, where can I get a good but cheap tri-shade card with black/gray/white on it? The kodak color chart was 40 effing dollars at B&H! It's a piece of plastic with colours on it man! What gives!


It's not cheap, but I picked up one of the PhotoVision 14" Pocket One-Shot Digital Calibration targets (before photovision bought out the original maker). They are around $40, but it made a remarkable difference in my exposure setting and white balance.

I use it like a grey card to set my exposure (manual mode) and then grab a quick frame. The three bands on the target make spikes in the histogram that make fine tuning very easy. I then set a custom white balance based on the target and it's usually dead on. If it's important, I grab one more frame afte the white balance has been set. I use that frame to help with curves or levels adjustments.

Probably the best $40 I have spend since buying the dslr.
 08/11/2006 01:35:05 PM · #9
Good tips guys. $40 bucks seems worth it but way steep for me right now. Man, this really stinks.

Whatelse do you guys have?
 08/11/2006 01:47:34 PM · #10
Shoot RAW. You should be able to get your exposure pretty close by using your histogram. Tweak it during RAW conversion by holding down the alt key while you adjust exposure and shadows (or doing the same in levels). Then tweak your white balance.
 08/11/2006 01:54:07 PM · #11
Originally posted by mk:
Shoot RAW. You should be able to get your exposure pretty close by using your histogram. Tweak it during RAW conversion by holding down the alt key while you adjust exposure and shadows (or doing the same in levels). Then tweak your white balance.

Or as a temporary stopgap, make your own. Create an image in Photoshop with Black/White/Middle Grey. Have it printed with a mat finish. Realize however that it is not perfect. It will be subject ot wear, fading, color variations due to reflections, color variations due to the type of lighting, etc.

The reason many of those Grey cards are so expensive is that they are designed with these issues in mind.
 08/11/2006 01:58:14 PM · #12
Originally posted by mk:
Shoot RAW. You should be able to get your exposure pretty close by using your histogram. Tweak it during RAW conversion by holding down the alt key while you adjust exposure and shadows (or doing the same in levels). Then tweak your white balance.


Yeah, you're right of course & that is why I did shoot in raw format. The gray card certainly helped in getting the colours right to the artisits' satisfaction but I wanna make sure the exposure is tip top.

_eug... I thought of printing out my own but was seriously adviced not to in another thread. I wanna get one but dont want to spend 40 beans on the bastard, ya know.
 08/11/2006 03:06:30 PM · #13
I don't totally follow how you use the spikes on the histogram to help w/ your settings but would like to hear more. Can you post a more detailed explanation or PM me?

Thanks

Originally posted by Nusbaum:
Originally posted by Rooster:

Also, where can I get a good but cheap tri-shade card with black/gray/white on it? The kodak color chart was 40 effing dollars at B&H! It's a piece of plastic with colours on it man! What gives!


It's not cheap, but I picked up one of the PhotoVision 14" Pocket One-Shot Digital Calibration targets (before photovision bought out the original maker). They are around $40, but it made a remarkable difference in my exposure setting and white balance.

I use it like a grey card to set my exposure (manual mode) and then grab a quick frame. The three bands on the target make spikes in the histogram that make fine tuning very easy. I then set a custom white balance based on the target and it's usually dead on. If it's important, I grab one more frame afte the white balance has been set. I use that frame to help with curves or levels adjustments.

Probably the best $40 I have spend since buying the dslr.
08/11/2006 03:43:13 PM · #14
I went with one of these WhiBal cards. they have changed it since I bought mine, but I like the new style better. hmmmmm
they are cards, but of solid (plastic?-something?) material that the color goes all the way through it, not just a layer on top.
The onw I have is the G5 version on the bottom of the purchase page.

Message edited by author 2006-08-11 15:51:37.
 08/11/2006 04:09:24 PM · #15
I know that not everyone can acquire it as easy as I did...I found where the facilities guy was hiding the spares.

but what I have been using lately for WB is a piece of one of the overhead flourescent light difussers (from work).

Not the smokey white ones but clear difusser with knurling on one side. Acts just like the expensive Optidisks or what ever they are called. Works a treat no matter what lighting you find yourself in. Hasn't let me down thus far.

Set the cam to Manual Focus and P-Mode, hold the piece of plastic (flat side) on the lens, Point at the subject and shoot... on the 20D we have to take a picture first and then set WB to that picture in the menu.

Home Depot or the likes might have something similar in the kitchen lighting dept.

Andy

ED: I did use a gray card for portant situations prior to using this homebrew disk...

Message edited by author 2006-08-11 16:24:50.
 08/11/2006 10:51:42 PM · #16
original
using gray point technique
This is an example using the technique from the thread I posted earlier. I saved it as an action and it took about a minute to fix. There is light from indoors and outdoors mixed together in this shot.
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