Open Photography Forums  
HOME FORUMS NEWS FAQ SEARCH

Go Back   Open Photography Forums > Color Management Discussion > CM Theory and Practice

CM Theory and Practice Profiles, color spaces, perception, science.

Reply
 
Thread Tools Display Modes
  #1  
Old October 15th, 2010, 08:26 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,519
Default White balance for the iPhone camera

Drew Strickland's firm, ColorRight Tools, LLC, has introduced a white balance color correction facility for the iPhone camera (and similar iOS based device cameras), the iBal for iPhone system. You can read about it here:

http://colorright.com/ibal-for-iphone-p-29.html

The hardware aspect of the product is the ColorRight iBAL White Balance filter, a small circular disk of translucent plastic that is held in front of the camera lens to make the measurement. It is essentially a white balance measurement diffuser.

The software aspect is an iOS app, available (free) from the Apple App store.

In the basic mode of operation, with the app in place, the app is activated for "measurement", the filter held in front of the camera lens, the camera faced toward the subject, and a shot taken. The software then analyzes the results of the shot and evidently establishes a "white balance color correction vector". The app then evidently causes the application of that vector when subsequent actual shots are taken by the camera, providing in-camera white balance color correction.

I think, from something I saw on the descriptive page, that with some cameras the system also accommodates measurement with the filter-equipped camera placed at the subject.

Test shots published by the manufacturer show images with correction applied that are probably more "pleasing" than ones of the same subject (we are to assume under the same illumination) without it.

**********

Those with an interest in how things work may wonder, as in the case of many of the ColorRight products, how a measurement taken from the shooting position, with the filter-equipped camera facing the subject, can determine what the camera needs in order to do white balance color correction: the chromaticity of the incident illumination on the subject.

The mystery is actually deepened when the manufacturer (as it does from time to time, in connection with some of its products) describes the process as working on the light reflected from the subject. After all, the chromaticity of that light depends both on the incident illumination and the reflective color of the subject. If the subject is large red barn, we do not want the camera to conclude that the incident illumination is way red.

And this outlook is emphasized when the manufacturer (not always in a clear way) touts what turns out to be a fairly-narrow acceptance pattern for some of their measurement diffusers (compared, for example, to the "cosine" pattern traditionally preferred for white balance measurement).
It is not that the manufacturer does something special to get that narrower pattern. Rather, it is inherent in any "simple" diffuser. They just don't apply any of the special features used in many other white balance measurement diffusers to create the cosine pattern.
So far as I can tell, the success of white balance measurement from the camera position in many cases relies on one or both of these:

In some cases, the average reflective color of the entire scene regarded by the diffuser is nearly "neutral"; thus the average chromaticity of the light from the scene nearly mimics the chromaticity of the incident light.

In reality, the diffuser-equipped camera really regards the chromaticity of the incident illumination on the camera. (It's not ideal for that, owing to its non-cosine acceptance pattern, but that is not a biggie in most cases where this is workable anyway.) In many situations (many outdoor settings, a ballroom illuminated by an array of identical chandeliers, etc.) the illumination on the camera is very similar to that on the subject.

So, like the drunk looking for his dropped keys under the streetlight, rather than in the alley, where he dropped them ("It's too hard to see back there"), we measure what is handy, and hope it is about the same as what we need to know.

In any case, Drew is to be congratulated for bringing his approach to white balance measurement to the world of the iPhone camera.

Best regards,

Doug
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are Off
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
White balance color correction Doug Kerr CM Theory and Practice 3 September 14th, 2010 02:42 PM
White balance and exposure determination Doug Kerr CM Theory and Practice 34 May 5th, 2009 09:39 AM
Camera Dojo reviews the Colorright white balance disc Doug Kerr CM Theory and Practice 0 June 18th, 2008 06:00 AM
In camera white balance (Canon) for flash shots Doug Kerr CM Theory and Practice 0 May 14th, 2008 09:13 AM
Some thoughts on white balance measurement diffusers Doug Kerr CM Theory and Practice 7 February 14th, 2008 03:52 PM


All times are GMT -7. The time now is 03:42 AM.


Posting images or text grants license to OPF, yet of such remain with its creator. Still, all assembled discussion 2006-2017 Asher Kelman (all rights reserved) Posts with new theme or unusual image might be moved/copied to a new thread!