Re: Understanding color balancing
Re: Understanding color balancing
- Subject: Re: Understanding color balancing
- From: Jim Rich <email@hidden>
- Date: Mon, 19 Dec 2005 20:28:53 -0500
- Thread-topic: Understanding color balancing
Lars,
I think Gramme is on the right track.
And....
My experience with software development goes back to the EFI program Cashe,
Photoshop and Color Studio. And based on those three experiences my guess is
that it will take one or two people a great deal of time to develop the
tools you are suggesting.
So two questions to consider are:
How much time are you planning to invest in this endevor?
How much money are you willing to risk?
If your answers are in the range of time and money is no problem then you
might consider going for it.
But if you come up with a different set of answers, such as I don't have too
much time and money, then you might find that your time is better spent
learning the set of mature color tools in Photoshop and taking pictures.
My .02.
Jim Rich
On 12/19/05 6:52 PM, "Graeme Gill" <email@hidden> wrote:
> Lars Vinberg wrote:
>> A short intro about myself since I am new to posting on this list: I am a
>> landscape photographer, work with film up to 8x10 as well as digital. I am
>> also a software engineer.
>>
>> I am trying to figure out how to make a color balancing tool for correcting
>> color balance in photographs. Ideally the user should be able to use a
>> dropper tool to click in neutral hightlights, midtones, and shadows,
>> possibly even more points. The tool should then make a correction of color
>> balance for the luminance where clicked. Possibly a UI similar to Photoshop
>> or Aperture.
>>
>> My question is: What is the proper way to do this, mathematically? The
>> working color space is an RGB space. My guts tell me that adjustments should
>> be made in chrominance only, keeping luminance fixed. Adjusting RGB curves
>> directly is of course a no-no. I could do corrections in Lab space but
>> calculations get a bit expensive. Is there a better way?
>
> Well, I'm no expert in this particular aspect (ie. I haven't had
> sufficient experience in actually making things that do this), but
> your guts are probably wrong. It seems to be generally accepted that
> black point adjustment (for instance), is best performed in a linear
> light space (ie. XYZ, or RGB without the gamma etc.), because this
> mimics the actual physical processes that create different black points
> (haze etc.) The accepted means of adjusting white points is to use a
> Chromatic Adaptation transform. If you are not familiar with this,
> it involves starting in XYZ space, converting to a cone sharpened
> space via a 3x3 matrix, adjusting the white point (a simple linear
> process, known as the "Von Kries" method), and then transforming
> back to XYZ space. Typically the sharpened cone space uses the
> "Bradford" matrix. This all mimics the processes that occur
> in our eyes, where our individual color sensors adjust their
> "gain", independently of each other. (Googling for some of these
> terms should return more information. There are a number of books
> that introduce basic color science out there too).
>
> As for mid tones, I'm not too sure. One could justify either a process
> in a linear light space, or in a L*a*b* type color space (that will
> preserve the neutral axis), depending on what underlying process you
> think is being corrected for. (Perhaps all three adjustments
> can be done in the Bradford space ?) Or try a number of these
> approaches, and see what works best. [That's actually what makes
> developing new stuff hard - exploring all the dead ends,
> until you end up with what works.]
>
> Graeme Gill.
>
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