WB & exposure with checkered card???

[myself62]

im not sure if this works,
i know that you can get white ballance and exposure acurate using a card which is divided into three tones, 18% gray in the middle, white on one side and black on the other, for example (white on right, grey in middle and black on left all on the same face of a card)

i have heard that a checkered card (like a chess board) will also act like a 18% gray card because it containes three tones (white, black and the mixture creating 18% gray)

so.. to the point.
can this checkered white and black card be used like the white/gray/black card mentioned above?

[myself62]

anyone??

[Mark_Cohran]

Never heard of that - or thought about it. For white balance the card has to be color neutral , i.e. no overall color cast in the pigmentation. I doubt game companies care much about how neutral the colors are on their boards. As far as exposure goes, I don't think it works that way for metering. 18% gray is considered the average tonal range for an average scene (more like 12.5% luminance according to some papers)- not the average difference between white and black, and even then, how pure is the white and pure is the black on a board. I'm sure there are other drawbacks to the "chess board" idea.

[Hermeto]

Well, I guess the OP could get 18% gray readout from the checkered card, but only if the lens is defocused all the way.
I’d rather use just the white piece of paper then the checkered one, though..

[vpnd]

what you are talking about I think is a exposure target card. They are used to dial in exposure. when you shoot it there should be 3 spikes on your histogram. If you expose correctly black should be at 20 (to barely show details in darkest area) one in middle (18 gray) and one spike at around 230-240 to get white properly exposed but not losing highlights. you I think are thinking of a white card. But imho about 3 or 4 pieces of white paper stacked together will get you about 1% away from a gnats tooth in a custom white balance. I hope it helped and didn't confuse more

[tzalman]

im not sure if this works,
i know that you can get white ballance and exposure acurate using a card which is divided into three tones, 18% gray in the middle, white on one side and black on the other, for example (white on right, grey in middle and black on left all on the same face of a card)

i have heard that a checkered card (like a chess board) will also act like a 18% gray card because it containes three tones (white, black and the mixture creating 18% gray)

so.. to the point.
can this checkered white and black card be used like the white/gray/black card mentioned above?

Are you asking about using this for exposure or for white balance, because they are two very different things. For exposure you need a target of known tonality and a grey card makes this easier because its medium tonality doesn't require you to make a compensation calculation. Color doesn't come into it. You could just as well use green grass or a brown envelope. OTOH, for white balance color is essential and tone is unimportant - the requirement is for a neutral white,gray or black. A gray card is preferred because it is the only medium that can play both roles conveniently.

As regards exposure: Canon's Evaluative metering weights the result toward the area around the active AF point. If there is none, the weighting defaults to the center point. I have also read that reference is made to a data-base of best exposures for similar distributions of tones around the frame, but I know no details about that. I have no idea how Evaluative would cope with a chekerboard. Not well, I expect. As for Partial and Spot, the reading would be very varible depending on the proportions of white and black in their viewing areas.

As regards WB: Custom white balance is done by the camera averaging separately the values of the three color channels within the central 9% circle of the trial photo and calculating the amount of digital multiplication needed to make the red and blue channels equal to the green. I'm not sure what the effect would be of the processor having to base its calculations on widely different levels of samples from within each channel, to say nothing of the fact that, other than luminousity, the white and black paint are likely to have very different color reflectivity spectrums, not only not neutral but also non-neutral in different ways. So again the answer is, unpredictable and therefore not dependable.

[Wilt]

so.. to the point.
can this checkered white and black card be used like the white/gray/black card mentioned above?


It depends...on the card. A gray card can be approximated with the right balance in the mix of areas of white vs. areas of black! There is no reason a gray card has to all consist of 18% density tone. It can consist of enough white vs. enough black that the mean is 18%. If anyone doubts this, simply pick up a newspaper (yeah, I know, a lot of the readers don't know what one of those is, including my own daughter!) and look at a photo. Those darker gray areas vs lighter gray areas are merely ink dots on the page, at different densities!

[myself62]

what you are talking about I think is a exposure target card. They are used to dial in exposure. when you shoot it there should be 3 spikes on your histogram. If you expose correctly black should be at 20 (to barely show details in darkest area) one in middle (18 gray) and one spike at around 230-240 to get white properly exposed but not losing highlights. you I think are thinking of a white card. But imho about 3 or 4 pieces of white paper stacked together will get you about 1% away from a gnats tooth in a custom white balance. I hope it helped and didn't confuse more

thanks for the responses. i wasnt sugesting that i was going to use a chess board, i was thinking of making one with a finer (smaller) grid of black and white, with that i would probably need to experiment to get enough white and black into the zone that the camera will use for the evaluation.
i also realise that the black and white needs to be the same shen level.

[Mark_Cohran]

I guess I just don't see the point. Why would you make one when gray/white cards are readily available from Kodak for just a few dollars?

[PhotosGuy]

You really don't need to make a card or buy a gray card. If you shoot white paper ON THE METER READING, it will photograph gray, just what the cam needs for Custom WB. It's pretty good for adjusting exposure too, when there are bright highlights that aren't important in the frame.
What’s best for exposure, Gray cards, white paper, expensive attachments for the lens?
Gray Card…White Paper. What’s best? (http://photography-on-the.net/forum/showthread.php?t=58677)

Don’t have a gray or white card for exposure, or hand held meter with you? “Film tricks” can help you out.
Need an exposure crutch? (http://photography-on-the.net/forum/showthread.php?t=89123)

[myself62]

I guess I just don't see the point. Why would you make one when gray/white cards are readily available from Kodak for just a few dollars?

i guess im just very curious to know if it would work, and thought that the three spikes in the histogram might give a better exposure reading, maybe i have had to much time on my hands this week (holidays)lol.

need to get back to work very soon :)

thanks for the comments.

[PhotosGuy]

and thought that the three spikes in the histogram might give a better exposure reading, It wouldn't hurt to have a white & black as reference. For me, it's simpler to have a calibrated monitor, get the whites "right", shoot RAW, & don't sweat the small stuff? ;)

[tonylong]

i guess im just very curious to know if it would work, and thought that the three spikes in the histogram might give a better exposure reading, maybe i have had to much time on my hands this week (holidays)lol.

need to get back to work very soon :)

thanks for the comments.

Your "three spikes" idea would be helpful if you are shooting jpeg or adjusting Picture Styles to make your LCD readout look like a good approximation to what an in-camera jpeg would look like. The gray spike should be in the center (some cameras are best being slightly right of the center, though). If your black and white points are too close to the center, you would up the contrast. If they are too far from the center you would lower the contrast.

The thing is, this only applies to a jpeg in-camera, or to the "starting point" picture style setting if you're shooting RAW and using a Canon-aware application such as DPP -- Adobe RAW/Lightroom apps don't adjust for Canon picture styles.

As has been noted, for White Balance, the equivalent of medium gray is what matters. However, the same note applies: in-camera white balance is applied to the jpeg and the Exif data. RAW converters take the Exif info and use it as a "starting point" that you can fine-tune as you will.