If you've worked with PNG files under Photoshop, you may have noticed that a picture saved with exactly 72 dpi has 72.009 dpi when you close it and open it again. Using an integer multiple of 254 for the dpi prevents such a drift.
Some things are just better bought from a reputable manufacturer than bodging your own. Photographic reference charts may well be one of them.
I've been using this for my photo adventures; I try to keep it in my wallet at all times (I worry about it getting discolored by rubbing against other cards though) and whenever I notice that the white balance is gonna get fucky (esp when there are multiple light sources) I whip that out and take a picture of it in the same scene.
edit: Also people love to use grey cards for getting exposure right but it's complete bunk science; if you're using the raw workflow (if you're fine tuning white balance you almost definitely are) you should shoot as bright as practically possible and not too bright to prevent clipping and adjust exposure as you see fit in editing.
Some photographers seem to worship color correction in a weird way. Other error factors, like reflected light hitting your calibration target, are likely to supercede any minor color imprecision from those kinds of printers.
- there is no such thing as perfectly black ink
- color printers will mix color ink into greyscale printouts
I know that early pilots had a series of markers that they could use to keep themselves on track as they flew their long distance routes. These things were oriented concrete markers, some of which are still accessible.
We all need a reference, a way to cross-check or ground truth our results and conclusions.
Though I note that that one looks suspiciously like the contra-recommended laser printed output.
Baader-Meinhof phenomenon - or did reading that Beeb article inspire someone to find and post this one?
I’ve done some little experiments but having a standard-ish thing is better.
Would this integrate to give scale, in say, Meshroom? Or it’s manual calibration step someplace along the workflow?
I’m in it more for the reasonably accurate 2d/3d measurements, but approximately accurate color is nice as well.
The way it works, iirc, is you can choose the model of your lens and the software fixes things. Works for professional lenses, unsure about others.
For more advanced stuff, look up CAHVORE models and related models.
The theory behind modern light metering is that if you average the "brightness" of every pixel (or the average density of crystals in the case of film) is should "visually" be around 50% brightness or density, or neutral grey. Spot metering on something that's already neutral gray sort of short cuts that process
For artificial light (or mixed sources, e.g. from reflections), it is not correct. The light source is characterized by its whole distribution (which can be anything) rather than one temperature parameter (for the Planck distribution).
An easy example is a fluorescent lamp spectrum (https://commons.wikimedia.org/wiki/File:Fluorescent_lighting...).
Another issue is that even if you have the perfect photography + post-processing setup, when I see the result it might be on a non-calibrated monitor, or on paper but in a room with non-perfect lighting, and perhaps I was just looking at something else a second before and my brain's auto white-balance hasn't caught up yet. So I might still not perceive it as was intended. This is why that gold dress looks blue to some people.
The patch of grey on the reference scale + good lighting of the scene to begin with will get you 99% of the way, the remaining 1% is extremely hard to get right, if at all possible.
In practice you do 2 anyway (with exposure correction being used even more often than white balance). So I agree that more than that is usually not worth the effort.
From my amateour photography experince - with strange lighting you cannot do much anyway.
Even a scene where there is strong sunlight and a bright blue sky will make white balancing quite difficult, as the shadows are lit with sky blue skylight and the sunlit parts are lit with the sun.
I use darktable and it's possible to correct the blue tint in shadows, but like... it's annoying. And at some point I'd say fuck it and just accept that photography is not a science.
If you care about accurate color, you do use a card with "whole bunch of patches" of different colors. For example, these British Library guidelines on photographing and scanning archival material say:
"An industry-approved colour chart or greyscale reference card is essential in
order to check the accuracy of the colour captured in the photographs. This is
a physical card that is available to purchase on the internet. It cannot be
downloaded from the internet and printed, or inserted into your image using
software. Approved colour checkers that have been used in EAP projects
include: Gretag Macbeth ColorChecker, QP cards, Kodak Color Control Q13
card, Past Horizons Bookmark Photo Scale."
ColorChecker (“Macbeth”) Chart: https://poynton.ca/notes/color/GretagMacbeth-ColorChecker.ht...
QP cards: https://www.argraph.com/QP202.html
Kodak Q13: https://www.kodak.com/en/motion/page/color-separation-guides...
Bookmark photo scale: https://www.pasthorizonstools.com/Photo_scale_bookmark_p/boo...
As you quote they get used in archiving but those also tend to be done under well-characterized lighting and if not, it's something that's worth spending the time to tweak every little thing.
It's a long shot from being able to apply automatic perspective and grey-point corrections plus a little bit of tweaking so the colors look "right" (or as right as possible under the wonky spectral distributions of most lights these days).
I did manage to convince the company to buy the transparency so we could calibrate the film scanner's output.
My favorites are from Datacolor or X-Rite.
Is there a standard skin color or something? How do you deal with different skin colors?