Problem with Color Cast Tutorial

Canon RF 24-70mm f/2.8 L IS

02/23/2005 07:40:54 AM · #1

Hi
I have two problems both of them are due to me not being good at PS. Well In the DPC Tutorial on â�� How To Remove COLOR CASTâ��
I am able to do fine till the point of setting White and Black Point but when I have to set gray point, I screw up, I mean I follow following the instruction properly

â�� in the Curves dialog box and then look around the image for a midtone color (not a shadow or highlight). When you move the dropper over the various parts of the image the number will change in the info box. Keep looking until the number becomes 128â��

But Instead of getting picture without color cast , my picture turns into a weird colored picture with sometime shades of blue, green etc., I mean like taking a normal picture and than as if some one has used channel mixer and increased value of one channel , say red or blue

I am using PS 7

Differences I observe between tutorial and actual working is that I never get the symbol sigma mark after choosing Total ink option , secondly I get only one percentage symbol when choosing value 128 I mean like in tutorial it is not 128/128 but simply 128

I tried another tutorial, //www.adobeevangelists.com/pdfs/photoshop/tipsandtricks/CorrectByNumbers.pdf

Quite similar to this but difference is that instead of asking you to creating â��Thresholdâ�� Layer it simply ask you take color sampler and choose one highlighted area and one shadow area, I Use threshold method as described in DPC Tutorial. Am I doing right? I mean If I use threshold method of DPC, technically when I am choosing White point and Black Point I am choosing Highlighted area and Shadow are

Secondly if person is wearing white t-shirt and black jeans and, when we use threshold method to set white and black point, wont first black and white areas be his jeans and t-shirt, so are these area correct actual mark., as sometimes I have done and RGB value is 255,255,255 or 9,9,9, technically meaning no color cast

Problem I face in this tutorial is that they tell you mark two color samples one of a Highlighted and second of a Shadow area, lets suppose highlighted areaâ��s RGB reading are 234- red, 209 green, 180 blue and Shadowâ��s reading are Red-90, Green-76, Blue 50 . Than they ask you to create Level Adjustment Layer, fine I do that and than they tell you see info palette and find the lowest Value among RGB in Highlighted area ( in this case it is Blue) than we are supposed to choose blue channel, take value of blue till 234 and do same for green i.e till 234, I do it but problem is that when I do I see value of Blue channel second color sample i.e Shadow area also changing . How can I remove this link, I mean when I want to change Value of Blue Channel of Highlighted area , Value Blue channel of Shadow area doesnâ��t change along with it . Reason is that I have equate RGB value of shadow are also.

Anyone know another Tutorial on Color Cast

Message edited by author 2005-02-23 07:42:55.

kirbic

Canon EOS R5

02/23/2005 08:28:18 AM · #2

Truth is, there is no one method that works best for all images. One method may woirk better for some images, another may work better for others. Your best bet is to become very good friends with the "curves" dialog. If a color cast is correctable, and most are, you can manage it in curves.
The problem you are having with the DPC tutorial seems to relate to the color sample you are taking to set the gray point. If the "true" color of the thing you are sampling is way off gray (has a significant color tint) the results are going to be crazy, something like you report. The trick is choosing something that SHOULD be gray (RGB value 128,128,128). Don't get hung up on finding something with that exact value, just realize that whatever you sample WILL be made that color, and everything else shifted accordingly.

02/23/2005 09:50:55 AM · #3

I use the adobe evangelist method, works well for me for people pics (haven't tried in on other items)
Highlights - the whitest and britest most blown out looking part of th epic (3x3 average remember) - ignore the other numbers of the other samples, you only care about the one you are working with.

shadows - the darkest item in teh pic.

midtones..18% gray technically, but i try for a shadow in a white area (the white shirt you mention) or the wall or ...take some experience. and this ONE adjust ment is done in CURVES, the other in LEVELS.

Post the pic and let me try

Nikon AF Nikkor 50mm f/1.8D

02/23/2005 09:54:14 AM · #4

Here are 3 exapmles of the same pic
original

my old method of fixing the color cast (using my eye)

and the 'by the numbers method'

David.C

02/23/2005 03:01:18 PM · #5

The tutorial here (and many elsewhere), are quick and dirty fixes that will get you close -- most of the time. However, they adjust the three RGB values as one.

WB is done by adjusting the mix of the RGB sensors in the camera -- how much weight (percentage) each is given in the final image. To correct a color-cast the RGB mix needs to be adjusted. It is adjusted at three points; white, black and grey. The best way to accomplish this is to do three times the work of the tutorial and adjust each of the color channels independently.

When choosing a point, as described in the tutorial, to set the black point (for example) the value of all three colors are being adjusted. That is, PS is setting the blackpoint for three different greyscale images in one step. For the black and white points this does not cause a lot of trouble usually -- but for the grey point it can produce a color cast if the mix of RGB in the pixel you choose is not correct for one or more of the channels.

To work with each channel independantly, create three levels adjustment layers -- one for each color -- and proceed for each one as the tutorial indicates. After all three points are set for each channel, you can fine tune the adjustment by moving the middle sliders of the levels layers.

Curves offers more control, as it allows any point to be set -- not just white, black and middle grey -- and you can set more than just the three. Levels -- like many other adjustments in PS -- is a simplification of Curves. It allows you to concentrate on a specific aspect of the distribution of color instead of everything at once. Curves is more flexible, since it can do anything, but with it you are also doing everything at once.

One more thing that may give you fits is if your image is lit by more than one color light source. Each light source will have it's own 'correct' balance -- but it is not likely they will miz evenly across the image.

David

02/24/2005 11:33:45 PM · #6

Thanks everyone, i think i am getting bit better

Canon EF 17-40mm f/4.0L USM

02/25/2005 08:28:29 AM · #7

Hi
Just wanted to know what am I doing wrong, I mark two color sample points, one for highlights, one for shadow. Highlight values are say 234,200,190. Shadow Value are 60,45,50

When I create Level adjustment layer and adjust for Highlight, i.e bring values of all channels same i.e Green and Blue channel at par with Red i.e at 234.

I donâ��t what am I doing wrong, I mean after I have adjusted values of Highlight i.e Brought value of channels equal i.e 234,234,234 Than I create another adjustment level layer to adjust for Shadow i.e bring values of all channels same i.e Green and Blue channel at par with Red i.e at 60.

But problem I face is when I increase value of say Blue Channel for Shadow from 50 to 60 ( to equalize with red) value of Blue Channel of Highlight also increase from 234

Sometimes it doesnâ��t happen like this, I mean when I increase blue channel in shadow blue channel in Highlight remains same i.e at 234

I really donâ��t what am I doing wrong

Ecce_Signum

Canon EOS-5D Mark II

02/25/2005 10:23:03 AM · #8

Originally posted by Prof_Fate:

Here are 3 exapmles of the same pic
original

my old method of fixing the color cast (using my eye)

and the 'by the numbers method'

Chris, I think that change is amazing!Did you do all 3 channels together or 3 layers? This is something I must try but it also shows the importance of getting the wb right in camera - something I shall be paying more attention to (even though I shoot raw now).

LEONJR

Fujifilm FinePix S3 Pro

02/25/2005 10:24:51 AM · #9

I noticed some on some tutorials that the same techniques arent exactly the same in CS.

Leon

Nikon AF Nikkor 50mm f/1.8D

02/25/2005 11:04:13 AM · #10

Originally posted by LEONJR:

I noticed some on some tutorials that the same techniques arent exactly the same in CS.

Leon

You can have my Ver 7 and I'll take your CS. Then you can follow the Tutorials better. OK? ;)

David.C

02/25/2005 02:29:08 PM · #11

Originally posted by General:

Adjusting one color of the hightlights (right slider) is going to affect the value of the highlights -- adjusting one color of the shadow (left slider) is not going to affect the highlights at all. The middle slider will not affect the shadow or highlights, just the distribution of the tones between them.

David

Nikon AF-S DX Zoom-Nikkor 16-85 f/3.5-5.6G ED VR

03/06/2005 06:37:35 AM · #12

HI
I have really improved, but I still some times screw up while setting gray point.

I am having success with Prof Fate way of setting Gray Point

i.e but i try for a shadow in a white area (the white shirt you mention) or the wall or ...take some experience. and this ONE adjust ment is done in CURVES, the other in LEVELS.

My question is that what RGB Values can be considered as Mid tones, Considering that fact I have color cast , if I take color sample for midpoint as Prof Fate said , than technically RGB should be different I mean I wont get 128,128,128 , so what individual value is considered as Mid tone Value , I mean if I get a color sample of 215, 132, 180 than as per his method I need to bring values of all channels equal where I need to choose one channel , in this case bluse and than decrease red channels value and increase green channels value.

As I mentioned I am having success with his method but really sure what to exact point to choose as mid tone value , I mean if I chosen another color sample from same region I chose first one its values are 220, 150, 160. So out of both which should I choose as my gray point.

Reason is that , my final picture still has some tinge but still a big big improvement , all thanks to Prof Fate method , But still not sure what RGB Value would be considered as mid tone values

PS
i use a digital camera which has auto wb setting, sun setting etc, color cast problem i get is when i use my camera's in built flash to fire my studio strobe's , since my camera is not meant to shoot with external flash and inbuilt flash is eTTl flash i.e it fires flash than based on that camera gets some info and than fires second flash. ( i read somewhere that it fine tunes wb setting and power of flash after first flash) . I use Wein digital peanut slave so that it ignores the first flash and fires strobes only second flash

cbeller

Nikon D300

03/06/2005 08:37:24 AM · #13

Originally posted by Britannica:

Adjusting one color of the hightlights (right slider) is going to affect the value of the highlights -- adjusting one color of the shadow (left slider) is not going to affect the highlights at all...

Actually this is not true. If you make large adujustments to the shadows, it will affect the highlights.

I normally adjust the highlights, then the shadows, and then go back and forth between shadows and highlights to finish evening them out. All of this done on a single adjustment layer.

cbeller

Nikon D300

Nikon AF-S DX Zoom-Nikkor 16-85 f/3.5-5.6G ED VR

03/06/2005 08:42:29 AM · #14

Originally posted by General:

...As I mentioned I am having success with his method but really sure what to exact point to choose as mid tone value , I mean if I chosen another color sample from same region I chose first one its values are 220, 150, 160. So out of both which should I choose as my gray point.

Reason is that , my final picture still has some tinge but still a big big improvement , all thanks to Prof Fate method , But still not sure what RGB Value would be considered as mid tone values...

Honestly, I skip worrying about the grey point when I am doing my adjustments. For me, when I adjust the highlights & shadows it does a pretty good job. If there is still a tinge (rarely), I may select a different highlight & shadow point and adjust again. If there is still a color cast (very rare) I make a selective color adjustment layer, select Neutrals and adjust for the color cast there.

03/06/2005 09:02:13 AM · #15

Originally posted by General:

PS
i use a digital camera which has auto wb setting, sun setting etc, color cast problem i get is when i use my camera's in built flash to fire my studio strobe's , since my camera is not meant to shoot with external flash and inbuilt flash is eTTl flash i.e it fires flash than based on that camera gets some info and than fires second flash. ( i read somewhere that it fine tunes wb setting and power of flash after first flash) . I use Wein digital peanut slave so that it ignores the first flash and fires strobes only second flash

Flash is SUPPPOSED to be equal in color to daylight. It is not...I shot in a friends studio, auto WB, big Ab800s for light. he also had some ambient light from outside - not much. i sot in RAW and could play with teh WB settings. Different ones (as shot, daylight and flash) gave slightly different skin tones. Nothing dramatic, and unless seen one beside the other, or you have a good eye, you'd never tell teh difference.

Does your camera have a hot shoe? You can get a hot shoe to PC cord adapter (got mine at ritz, $9). The PC cord was another $20... Anyway, you can now keep the on-camera flash off. Shoot in manual mode! A flash meter is best of course, but you can set the camera via the histogram after a shot or two.

As for setting the gray point...I am still expereimenting with that. Just as soon as i think i know what i am doing, i get an image that won't behave as expected! While i think of mid-gray as 128/128/128, my Kodak gray card is much darker than that.

Canon RF 24-70mm f/2.8 L IS

03/06/2005 09:11:07 AM · #16

Thanks for replying, but adjusting only black and white point doesnt really remove much of color cast but when i adjust gray point , it makes one hell of a difference but tinge i was refering is very less i think reason i am asking how to set gray point is because i really want to be sure , what is the right way .

i mean how to set black point and white point is crsytal clear but when i would try adjusting gray point as per DPC tutorial i would get crazy result and when i tried Prof Fate method , i atarted great result just was not sure criteria of choosing a gray point if i had wide range of objects to choose from.

I mean if same object gave me two color samples 220, 150, 160. and 215, 132, 180 which one among both should i choose

kirbic

Canon EOS R5

03/06/2005 10:53:34 AM · #17

There is really no one right method, nor one right gray point for any shot (except perhaps of a standard color target). Use the method that gives you the results that you think are best.
I often set a "black" and "white" point separately for each channel and then tweak from there. All depends on what look I want in the final image.

MWitt

Canon EOS-5D

Tokina AF 28-70mm f/2.8 ATX Pro-SV for Canon EOS

03/06/2005 11:29:58 AM · #18

This tutorial was posted a while back and it helped me with color casts.
Give it a look, Gagan!

Try page 104, but read the whole article.

Color Correction