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Forum: Flashes, Lighting, and Studio
02-20-2019, 04:22 AM
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Absolute accuracy has never been my own aim with camera profiles either, but of course I completely accept that for many people as much objective accuracy as possible will be the goal. I'm just interested in getting results that I personally like, although thanks to this thread I've now discovered that I've been creating profiles that I like with a test card that isn't actually accurate.:o
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Forum: Flashes, Lighting, and Studio
02-20-2019, 02:15 AM
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Thanks for the link to the other thread. Could I perhaps clarify a couple of things about the two different threads, just to avoid confusion for anyone who happens along here and doesn't read through the whole discussion?
My understanding is that your other thread is about your wish to be absolutely sure that your monitor is perfectly calibrated, beyond the level of calibration that most of us do with things like Spyder (in my case). So, to be sure of that, you've wanted a completely accurate image of a ColorCheck card that you can look at on your screen. And the ColorCheck image that you're referring to above is one that you've downloaded from x-rite to use as a neutral reference on your monitor, rather than one that you've shot with your own camera and lens.
That's a completely legitimate thing to do if you want to be absolutely sure about your monitor's calibration, but it's not really what this particular thread is about. And I'm sure you're already aware that the downloaded test card image from x-rite would be of no use in creating a custom camera profile.
This thread (at least as I've personally interpreted the OP) is about how to shoot test cards with our own cameras and lenses to create custom camera profiles, which has nothing at all to with monitor calibration. We've been talking about things like which illuminants to use, whether we can be sure if the colours in our test cards are still stable after a few years, how the colour characteristics of different lenses affect things -- all the many variables that we have to consider when creating our own custom camera profiles.
This is absolutely not a criticism of your other thread or your valuable contributions to this one. I've personally found the other thread fascinating and informative, but I do want to keep things clear about the different aims underlying the two discussions. Camera profiles and monitor profiles are completely different things, and I think it's important that we avoid any confusion between them, just to help out any newcomers to the concept of profiling who might come along.:)
Edit: I should also mention that I've discovered that I get different white balance values from the white and mid-grey patches on my own test card, when of course they should be the same. I've concluded that the inks are no longer accurate on my own card, so I'll be getting another one. Any pink cast that anyone sees in the examples I posted above is down to the card used no longer being accurate, so apologies for causing confusion with that.
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Forum: Flashes, Lighting, and Studio
02-16-2019, 01:50 PM
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The pinkish cast that you both mention might well be real. It could be that the inks have shifted slightly in the test card (it's five years old), or it could be a characteristic of the lens used (the choice of lens has a significant impact on custom profiles), or it could be an ambient light intrusion because I shot the flash and LED cards in my living room this morning without setting up my light tent (I was a bit hungover after a great night with good friends). The bottom line is that there are so many variables when it comes to creating custom profiles that you can drive yourself nuts trying to iron them all out. My aim was simply to show how small the differences actually are between different illuminants, and I don't feel that a slight pink cast undermines that point even if it does exist.
The daylight LED is a SAD light box that I use when too many days of Dartmoor winter gloom start getting me down. It claims to be full spectrum, but I think the test card example shows that the spectrum is actually far from flat.
As for the averaged profile: when you use the "chart" tool in Adobe Profile Editor it shows you the values that it has used for the 16 colour patches out of the total 24 on a standard Macbeth/ColorCheck card (the monochrome values are implicit in the 16 colour values). I just averaged out the values for the three different light sources used in this very basic example. If 16 values doesn't sound like enough to create a profile, remember that the software then twists the entire colour space around those coordinates.
Folks, you are never going to be able to cancel out all the variables and create an absolutely objectively correct profile on your own. You just can't. But even with the most basic work you'll end up with something much more accurate than the manufacturer's embedded profile, because accuracy isn't the embedded profile's aim. The embedded profile just wants to make you say, "Wow, look at those amazingly bright and punchy colours!" Custom profiles are for when you're after something a bit more subtle than that.
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Forum: Flashes, Lighting, and Studio
02-16-2019, 06:26 AM
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It's been a cold wet morning, so I've played around with some profiles. This first set is three profiles created using Adobe Profile Editor from the same test card shot under different lighting. The top one is mid-day summer daylight from last year, the middle is flash, and the bottom is a daylight balanced LED light (I accidentally put LCD on the comparison, but it's actually LED).
 Combined by David Holland, on Flickr
As you can see, there are some differences presumably caused by the different spectra of the different light sources (and perhaps slight exposure differences, although I tried to match them as close as possible). I usually shoot in daylight using the same daylight profile shown here. I never personally use flash, but if you are a regular flash shooter I think it would be best to create a separate profile purely for your flash shots, as the differences between the daylight and flash examples above seem to justify it.
Now here's the test card that was originally shot in daylight, with the daylight profile applied at the top and an averaged profile at the bottom. The averaged profile was created by averaging the values for each colour patch in the daylight, flash and LED profiles. (When you're creating custom .dcp profiles using APE, you only need to worry about the 24 patches on a standard Macbeth/ColorCheck card. The software then twists the colour space around those values automatically, and also extrapolates the tungsten profile from your 6500K original.)
 Combined 2 by David Holland, on Flickr
It seems to me that just these three profiles combined averages out to something very close to the straight daylight profile on its own. I'd suggest that the more different artificial light sources you average out, the closer you'll get to something that's indistinguishable from daylight. In which case, if you want one general purpose profile, you might as well just shoot the test card in daylight.
And how does any of this apply in the real world? Here's a random shot converted from raw to jpeg using my normal daylight profile on top, and the averaged profile at the bottom. Even just averaging out three different light sources seems to me to result in a difference that's negligible in real-world photography. I'd expect it to be impossible to detect any difference at all if you averaged out enough different illuminants.
 Combined 3 by David Holland, on Flickr
Ah well, that kept me happy for a couple of hours on a wet Saturday morning. The methodology was definitely more rough-and-ready than lab-grade, but I hope it gets the basic idea across.:)
(Note: all test cards were shot using the Pentax K-S1 and SMC Takumar 24mm/3.5, so the equipment used is the same in all examples.)
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Forum: Flashes, Lighting, and Studio
02-15-2019, 01:59 AM
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This thread is making me wonder about the possibility of shooting the same test card under multiple light sources that all have a nominal 6500K but not flat spectrums, then averaging the results. Since Adobe Profile Editor shows you the values it's using for each colour patch and allows you to edit them, creating an averaged profile wouldn't be too hard.
I might give it a try over the weekend.
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Forum: Flashes, Lighting, and Studio
02-10-2019, 02:14 PM
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Thank you, that looks like it's definitely worth trying. The main reason I'm still using Camera Raw/Photoshop is my need to use .dcp profiles, so a user-friendly way of creating ICC profiles could finally liberate me from the clutches of Adobe. And that would get rid of the last reason why I'm still using Windows, so I could go full Linux.:)
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Forum: Flashes, Lighting, and Studio
02-10-2019, 02:55 AM
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I just use direct mid-day sunlight, then use the eyedropper to correct the white balance to the white patch on the test card and save the raw file with that WB. It's not a laboratory grade approach, but for creating dual-illuminant .dcp profiles using Adobe Profile Editor it works well enough for me. I actually base my profiles on test cards shot at noon on June 21st, because the variation in the ambient light from pure daylight in my part of the world is what I'm interested in capturing in my photos.
Creating ICC profiles is more difficult and I've never done it. Custom profiles are so crucial to my own approach to digital photography that I'd only ever use a raw converter that could handle .dcp.
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