Correcting WB with JPEG

[MediaMagic]

Okay, today I screwed all my little league football shots. About 175 shots large/fine JPG. This was early morning in extremely bright sunlight. I had set the camera for tungsten shots last night and forgot to reset if for sunlight today. Every shot has a bluish cast because of the white balance. I couldn't tell by looking at the LCD, it wasn't until I saw the full images on the screen that I realized what I had done.

Now, I have another problem. My monitor is not perfectly calibrated. I used Adobe Gamma to get it close, but I know it is still slightly off, so I can't trust what I see to correct the shots.

Does anyone know the correct numeric correction for the hue channels to convert from tungsten WB to daylight in PS? Or another way to make this correction mathematically rather than having to go by what I see on the screen?

Thanks,
David

[dmalek]

a solution can be to set the white point with photoshop.

open the file, then run the levels adjustment dialog window, choose the white point eyedropper, click on the picture in a white area and this should help get better colors

[Dans_D60]

Of course, the only way to truly adjust white (gray) balance is from RAW images before they are processed and transformed to any other formats. Once transformed to JPEG the ability to adjust white balance, contrast, and exposure is very limited. However, Photoshop and most other advanced editing applications allow some tuning and adjustments. For those who shoot JPEG and want to alter white balance can try Photoshop’s “AutoColor” or select “Levels” and the middle eyedropper like so:

IMAGE – ADJUSTMENTS – LEVELS.
Use the Middle Eyedropper and click on a white or gray area in your image:

http://www.pettusphoto.com/wb/wb1.jpg




This image should have a LIGHT PINK background and the petticoat is pure WHITE as shown next:

http://www.pettusphoto.com/wb/wb2.jpg


As far as calibration, I highly recommend the “Spyder” device by Colorvision. My monitor is adjusted very close to printouts. I have a 20” SONY Trinitron and the printer is the Canon S9000.

You may want to consider using the “Expodisc” for foolproof WB while shooting. This device fits on the front of your lens and will always read 18% gray from the image you are attempting to shoot. I have one but it hasn’t found its way into my daily workflow. The site to purchase this device is: http://www.expodisc.com

Hope this helps!

Dan
http://www.pettusphoto.com

[Rob Larsen]

MediaMagic wrote:
Does anyone know the correct numeric correction for the hue channels to convert from tungsten WB to daylight in PS? Or another way to make this correction mathematically rather than having to go by what I see on the screen?


David, Dan's method using the PS Level's eyedropper(s) is probably the fastest way to neutralize your colors. You can also use the Levels tool to "numerically" fine tune your color balance if desired. Here is the method to numerically tune your highlights, midtones, and shadows:

1. Find at least 3 neutral areas (or what should be neutral) in your image that represent highlight, midtone, and shadows. This method will tune each individually. A Threshold adjustment layer may help you identify your highlight and shadow areas.

2. Use the Color Sampler eyedropper to mark each of these areas. You will monitor the RGB values for each of these points using the Info pallet.

3. Add a Levels adjustment layer. Each tonal area will be adjusted "numerically" using the Input Levels fields in the Levels dialog box. They represent shadows, midtones, and highlights respectively from left to right. Your Info Pallet shows the RGB values for each color sample in the form of xxx/yyy. xxx being the current value and yyy being the value after your changes. Your goal is to get all the "yyy" RGB values for your highlight color sample to equal each other, thus neutral.

4. Starting with the highlights, put your curser in the highlight Input Levels field (far right) in the Levels dialog box (see Dan's illustration above for reference). For highlights, note the brightest of the RGB values (highest number) shown by your highlight Color Sampler on the Info Pallet. You want to make all highlight RGB values equal this number. Raise the highlight Input Value for the individual color channels until they equal this number.

Do this by selecting the color channel (R,G, or B) you want to raise in the drop down menu. Put your curser in the highlight Input Level field and use your up/down arrows to adjust the value until it equals the brightest value of your highlight Color Sampler. Here is an example of how your Info Pallet would look after adjusting your highlight sample:

.... Original ............... Goal
R: 221/221 ............ 221/226
G: 226/226 ............ 226/226

[MediaMagic]

Thanks a million everyone!

This information has been an invaluable help in getting the photos to the proper color balance. I used the photos Dan posted and a combination of the eyedropper selector and the numeric transformations to get my pics to appear the same hue as the white petticoat (known white) in Dan's shot. This is the strangest bit of editing I've ever done, i.e., trying to get photos to match a level of visual incorrectness (but actually being correct).

My monitor is dying, it cannot be calibrated. A 19inch sony circa 1998. It's time to break down and get another. Of course, it decides to go T/U after I spend all my money on lenses. I was planning to get a Sony F520 with my Christmas bonus (I love that .22 pitch), but there's no way I can wait that long. I'll have to come up with an interim solution.

Thanks for bailing me out in this one, you guys saved the day for me.

David

[design crusader]

The only thing I wanted to mention in setting your highlight, midtone (neutral gray) and shadow is that you want to use them to not only set the correct color, but also set the correct luminosity of your image. In other words, you don't want the highlight to be pure white (such as a stellar highlight or reflection), you don't want your shadow to be just the darkest area; instead, try to find something in your image that you know is to be a true black. And finally, set your eyedropper to read grayscale values and then try and find a neutral gray in your photo that has a grayscale value of 50, and that is where you would want to click with your Set Midtones eyedropper in your Curves or Levels dialogue box.
Ideally, if you could use a test card somewhere in your photo composition that had a true white, gray, and black -- then, in Photoshop you would use it to assist in white balance/color correction.

And as stated earlier in this thread, the EXPO disk seems to work quite well for setting Custom White balance to a neutral gray for that specific image exposure.