Red is my nemesis

[purplehaze]

I never seem to be able to reproduce the original colour, even on the rare occasions when I remember to include a grey card. Tips on shooting red welcome, as well as any other observations you might like to make.

[Colin Southern]

Hi Janis,

You need to be very careful not to over-expose shots with dominant red in them. The red maxes out the "R" channel on the sensor, but because it's only 1 channel, doesn't trigger a highlight alert ("blinkies").

If your camera has an RGB histogram, now is the time to turn it on!

[Colin Southern]

[purplehaze]

That looks great, Colin! Did you just drop the exposure or what? Back to the virtual darkroom I go!

[Inkanyezi]

The virtual darkroom is actually not the place to correct for over-saturated colour, but in the jpeg you supplied, there does not seem to be over-saturation (over-exposure) of the red. However, it shows obvious signs of having been edited in software already, and from the jpeg it might be difficult to get very good balance. This kind of corrections should preferably be done from RAW, where there is more data, and no colour correction is done yet.

So if you have the RAW file, the virtual darkroom might be the place to manage colours and tonality, as most likely, there can be sufficient data in the RAW file to render good tonality over the whole image.

And although the dark/bright control of the software maybe is marked "exposure", it is not exposure that you manipulate, as it is done when you press the shutter release. Any later editing does not alter exposure, and that is why, if the red is clipping, a lower exposure must be chosen when shooting the image.

The histograms - individual three colour histograms - are a good help to evaluate whether exposure is too much to the right so that information is lost, or if there can be data for all tones in each colour. However, camera histograms are evaluating the in-camera jpeg image, also when you shoot RAW, so sometimes, the RAW image may contain data that is not evident from the histogram. If however, you do not shoot RAW, but save your images as jpegs, the histograms tell the truth of the image you captured.

There is a consideration regarding your "grey" card. All of them aren't. I have tried several grey cards on the market, and found none to be grey; they all produced colour casts when used for white balancing. As far as I know, there is but one that is declared spectrally neutral, i.e. reflecting all spectral colours equally. It is the WhiBal card, which is in fact not a grey card intended for measuring light, but a white balancing card only intended to white balance correctly. It is designed for white balancing and can facilitate your virtual darkroom work significantly. But it is not intended for exposure reading, and there is to my knowledge no light meter that is predictable enough when it comes to saturated colours. The safest bet sometimes would be bracketing exposures, which is a reasonable technique when working with still subjects.

[purplehaze]

Thanks for your reply, Urban.

The virtual darkroom is actually not the place to correct for over-saturated colour, but in the jpeg you supplied, there does not seem to be over-saturation (over-exposure) of the red.

I am in fact shooting RAW on a Nikon D90 and editing in Aperture 3. When I went back and checked, I found that if I zero "Boost" and "Hue Boost" in Aperture, there is next-to-no clipping of the red, and the bit that there is is easily recovered using the Recovery slider.

However, it shows obvious signs of having been edited in software already

I am curious to know what those signs are.

So if you have the RAW file, the virtual darkroom might be the place to manage colours and tonality, as most likely, there can be sufficient data in the RAW file to render good tonality over the whole image.

I have been trying, since Colin's and your posts, but the colour of the darker tones goes quite muddy. I don't quite know what to do about that, but I will keep experimenting.

And although the dark/bright control of the software maybe is marked "exposure", it is not exposure that you manipulate, as it is done when you press the shutter release. Any later editing does not alter exposure, and that is why, if the red is clipping, a lower exposure must be chosen when shooting the image.

So are you saying that the control marked Exposure is really just a Brightness control that affects all tones, as opposed to the Brightness control, which controls mid-tones only? Are clipped tones never truly recoverable?

However, camera histograms are evaluating the in-camera jpeg image

Good point; I will try to keep that in mind.

There is a consideration regarding your "grey" card. All of them aren't.

I have a Digital Gray Kard. Do you have any knowledge of experience of that brand?

Thanks again, Urban. Between you and Colin, I have done some learning here.

Btw, in my fiddling last night, to resolve the muddy colour issue, I did this b&w conversion. Better tonality, no?

[Inkanyezi]

The obvious sign of editing is a jagged histogram.

And yes, the "Exposure" control in software controls brightness. It is called exposure, because it simulates exposure, but the actual exposure is when you open the shutter to let the sensor receive light. In some RAW converters, clipped mix colour may be simulated, by adding data to the clipped channel after making the clipped portion a bit darker, but in fact, clipped can never be truly recovered. It does not apply to one clipped saturated primary colour. When one colour channel is clipped in a saturated primary colour as red, there is no data to fetch from the other two channels that can be used for simulation of recovery, hence no recovery can be done.

I have no experience with your grey card brand, but from the few that I tried, among them my old Kodak grey cards, I did not find any that works for white balancing. In fact, I tried out a few substitutes and found one plastic food container that is reasonably spectrally neutral, and the other substitute, that I recommend using when other means are missing, is household or toilet paper, that is bleached, but not treated with optical whitener, usually the cheapest kind as sold here in Europe. It is very close to spectrally neutral.

However, the WhiBal catd is measured and complies to strict specifications. I haven't found any other grey card producer that uses such strict measuring methods or specifies each card to be within narrow limits of spectrally neutral. So my best guess is that if you did not get a measurement protocol with your card, it might be insufficiently neutral for white balancing. I'd suggest that you look through the videos that Michael Tapes made and pay particular attention to the sixth one, that reveals a lot about "gray cards" that you may find in the market. The videos can be found here:
http://www.whibalhost.com/_Tutorials.../01/index.html

As you white balance, it helps to have much data in the reference area, and therefore a brighter tone than the standard 18% is better, as your software or the camera may evaluate it better. That is the reason why the WhiBal card is not 18% grey, but a much brighter tone. It shall not be too close to clipping, but the best is if your white reference falls above Zone VI, for example in Zone VII or VIII. Measuring light directly from the balancing card and exposing one stop brighter does the trick, provided the card is really neutral, reflecting all colours of the spectrum equally.

You also might do a quick check with the toilet or household roll of paper as I suggest, taking a photo of the rose with your cards and the paper (without optical white "brightener") included in the photo and white balance in your RAW software. If there is a difference in colour or tonality, we could argue over which "grey" is more neutral. Either way, the WhiBal card is certified to be spectrally neutral within close limits.

The rose below is processed to jpeg by the camera, a Panasonic Lumix G1, exposing two steps below what the meter suggested, in order to retain tonality in the red petals. The green leaves suffered a bit from the low exposure and got murky, as the sensor does not have as large dynamic range as yours. The D90 has a very good sensor with large dynamic range and should do better.

[purplehaze]

Thanks for your very thorough reply, Urban; I would have replied sooner, but was without a reliable connection for the last couple of days. I definitely will take a look at those white balance tutorials and go look for some red to practise on. Given the heat wave we are in, I may need look no further than me!