Competing Contrast controls in Camera Raw (and Lightroom)

[tonybrown]

There's an oddity in Camera Raw: Under "Basic" you can adjust Contrast, for example to zero. Under "Tone Curve",

select Point, and you can preselect Linear, Medium, Strong and Custom Contrast. Both the Basic and Tone Curve

controls operate independently, simultaneously. So for example under Tone Curve you can select 'Linear" and under

Basic you can adjust for High Contrast, setting the contrast control to 100. What you get is the combination, neither

linear nor high contrast. So if I want to go really linear (using all 14 bits available in Canon's 1Ds mk III) I set Basic

Contrast to zero and Tone Curve to linear.

Surprise: its the same in Lightroom 2.

So, wouldn't it make sense to give the Basic and Tone Curve controls exclusive control of contrast - either one or the

other? Am I missing something here?

[colin_mattson1]

They're meant to be independent, because they're not both "contrast" tools. (Bear with me here.)

 

The contrast slider is the overall contrast tool; it acts on the entire image in a fairly uniform manner, giving you more or

less overall contrast. Simple, easy, bang boom done.

 

The tone curve, while it can be used to alter contrast, isn't a contrast tool per se -- it changes, as the name implies, the

tonal curve. If you think back to film (assuming you used film), the tone curve adjustment lets you set your

characteristic curves. Yes, those curves will to some degree affect the contrast, but that's not their only purpose.

Shoulder, toe, control over gradations, shadow, and highlights... That's what the tone curve adjustment is for.

[tonybrown]

Colin, I appreciate your explanation. It does line up with some of the articles on the Adobe web site. The fact is though, the 'Tone Curve' does have a preset (forget the curves) which permits adjustment to linear, medium, strong and custom contrasts and these modify the contrast that you set with the contrast slider in the basic mode. Probably no contest there? So what combination of the two contrast controls is equivalent to the native contrast of the physical optical sensor? Is it zero on the basic slider and linear on the tone curve preset?

 

Further, Adobe suggest that the tone curve is a fine adjustment tool. That would be ok, but the tone curve preset works all the way from linear to strong contrast. In that way it competes with the basic slider adjustment. I've worked with this for a while, and it still puzzles me. In practice I do have two methods of strongly controlling the contrast and they are not independent.

 

Granted that you can use the basic slider control to get the contrast that "looks" right to you and as you said - simple, easy, bang boom done. But I would really like to know how to get the native contrast set by my camera before making adjustments. This has implications for noise etc.

 

Tony

[tonybrown]

Here's an example of how this in practice affects my work. The Canon 1Ds mk III has 14 bits of resolution as oppopsed to the usual 12 bits. The extra 2 bits are used in the highlight range so that wedding photographers can extract fine detail from wedding dresses etc. Under normal photography these 2 bits are under-utilised. So in photographing a rose, I deliberately overexposed by 2 stops, giving me extra dynamic range. (There are some articles on this). Importing into camera Raw indicates the rose is grossly overexposed, but adjusting exposure in Raw brings the highlights into visible range and at the same time pushes the noise down two stops. In order to preserve some of the detail in the low lights I need to reduce the contrast - a linear contrast becomes my target. So I set the contrast to zero on the basic slider and to linear on the tone curve preset. And I end up with a beautiful rose with some really nice delicate lighting of the petals. Clearly I don't think that high contrast is advantageous in this case. http://www.photo.net/photo/7539538

[jeff_schewe]

Tony,

 

The primary reason why there's 2 controls (with 2 flavors of the second tone curve editor) is for complete backwards compatibility. When the point curve editor was added, they could have taken the basic panel contrast adjustment out,

but that would have caused perviously set images to either ignore the old contrast only settings or try to force fit the old

settings into a curve setting. It was easier in many way to simply add the point curve editor while keeping the contrast

slider as a separate adjustment. Yes, it might be simpler to just bad the old stuff and add new stuff, but first and

foremost, the engineers want to preserve the work people HAVE already done on their images so versioning is a very

complicated issue. One they will have to solve in the future (and are working on).

 

So, at the moment you in effect have 3 different approaches to adjusting the tone curve; the Basic Contrast slider, the

Point Curve Editor and the Parametric Curve Editor...and truth be told I really think you should re-think trying to process

out of Camera Raw with a linear or flat tome curve and try to fix the image in post work in Photoshop. That's not

optimal...

[tonybrown]

Jeff,

 

Thanks for the insightful explanation. I had wondered if there was some historical lagacy effects that influenced the current situation.

 

On the camera Raw editing question, versus editing in Photoshop, I think the choice depends on the image. I can achieve a larger dynamic range in Raw, and if I don't do that in Raw it's too late to do it in Photoshop. Anyhow, Christmas is coming and there's a copy of Lightroom 2 under the tree - which I understand does everything in Raw and does it well. Maybe I'll have more to add next year.