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using gray cards
- Thread starter Pog
- Start date
Joe Calabrese
Well-known member
Its basically another way to white balance. You place the grey card somewhere in your image, and that way the software know what the value should be, like R178 G178 B178, and corrects the grey in your card to what the know value should be. It adjust all the colors in the same way (adding more red or green, for example) to make all the colors as accurate as the grey was compared to the captured image.
Its easy, I probably just didn't word it right.
Its easy, I probably just didn't word it right.
j1clark@ucsd.edu
Veteran
Hi,
Have any of you folk heard of filming a grey card and using it as a colour / exposure reference in post? Is this necessary? I read something about this but not sure if what i read was correct
A 'grey' card is not particularlly for 'color correction', a 'neutral white' card/screen would be for white balancing...
A grey card, the 18% grey card, should be used to set your '50%' value. If you have a video waveform, modern cameras are including that feature, the grey card should yield a wave form that is in the 50% IRE (or approximately 50%).
This of course may not set the camera for the scene lighting...
Light meters are set up, at least with 'film', for a given ISO value, to yield an exposure which will result in a 18% grey card being approximately a middle grey value in the resulting print.
Hence, an exposure meter's reading needs to be 'contextualized' to what is being metered... if the object being metered is a 'very white dress', then the meter reading designed to yield a middle grey, needs to be adjusted for the 'white dress', that is the reading openned up 2-3 stops. Caucasian skin, is about 2x reflective as an 18% grey card, so, a meter reading off of such skin, needs to be adjusted by +1 stop. Dark complexion persons, vary between 18% reflective, that is 'middle grey', and one stop below middle greay, that is the meter reading closed down by one stop.
I've not gone through the exercise of matching up IRE % readings, grey card, and various reflectivities, in detail. I have Adobe "On Location" which has wave form monitors, and so I'll probably look at this more with various objects, and reference them to the grey card, and the IRE % readings on the wave forms.
So when filming folk with darker skin ya can set your auto-iris using a gray card.
Are any of ya familiar with using a 'Colour Reference Card'? Do many of ya use them? This i heard will usually have squares of different colours on it and can be used (amoung other things) to match one shot to another in post.
Are any of ya familiar with using a 'Colour Reference Card'? Do many of ya use them? This i heard will usually have squares of different colours on it and can be used (amoung other things) to match one shot to another in post.
Last edited:
j1clark@ucsd.edu
Veteran
So when filming folk with darker skin ya can set your auto-iris using a gray card.
Are any of ya familiar with using a 'Colour Reference Card'? Do many of ya use them? This i heard will usually have squares of different colours on it and can be used (amoung other things) to match one shot to another in post.
Since I'm coming from a still photography background, I don't know what film/video people may use for on set color calibration. The only time I would use a calibrated color card, is if I was documenting something like art work. The books print art reproductions 'all over the place' in terms of color casts, or outright color whackness.
Some galleries are now supplying 'publication' digital images, and some have a color card in the shot so people can better match the actual color of the art work in their reproductions.
In some cases the color shifts are not just because of the limited print color gamut, but outright 'shifts' because perhaps the printer had no clue about what the original was, but made changes to make, say skin tones more 'natural'... when in reality, the artist used a green/blue twinged color...
But I digress...
If there are a large number of significant 'colors' in a shot, I would imagine some DoP's take at least a test shot during setup with a color card in it for calibration at the lab. That way any shifts, due to process, film stocks, etc. can be 'dialed out'. With the use of digital intermediaries these days, this would give one a 'neutral' transfer mapping.