I always thought white balance should be done off of a white card not that I understand how (why might be a better term) selecting an area of a color (or even multiple colors) adjusts all colors or how it does it. I would think if you should select a 18% gray/ x brightness white card area the computer should adjust that area to be that gray/white and adjust the RGB colors around it to match. That is what I meant originally.
In any case..... how do you use the gray card to set exposure. (also.... please cc the list because the only reason I got this message from Lorenzo is because it was in someones inline) > 2017-02-22 8:36 GMT+01:00 Lorenzo Bolzani <l.bolz...@gmail.com>: >> >>> Printing a gray card is a bad idea: you need a very good an perfectly >>> calibrated printer for this and good non-glossy paper. Otherwise you do not >>> get perfect gray and you get a random shade of color in all your shots >>> where you use it. Just buy one. >>> >>> For white balance, as Ivanov said, any gray is good, actually you >>> typically use a white card. So *just take a white sheet from the >>> printer a use that.* I did this in several occasions and works really >>> fine. The minor problem is that paper is not "perfectly neutral white" but >>> can vary slightly so if you are looking for ultimate perfection buy a WB >>> card (X-Rite, Opteka, etc.). >>> >>> The gray 18% thing is about setting the exposure, not the white balance. >>> Of course you can use the gray card for white balance too but it's not its >>> main purpose. Typically gray 18 targets are white on the other side for WB. >>> >>> Often white balance cards came in set of three pieces: white, gray and >>> black. Almost always the gray here is not gray 18 so it is not good for >>> exposure reference only for WB. >>> >>> >>> Bye >>> >>> Lorenzo >>> >>> >>> 2017-02-22 5:57 GMT+01:00 I. Ivanov <iv3...@gmail.com>: >>> >>>> For the purpose of white balance - I don't think it really matters if >>>> it is 18% or less or more. It is just pure gray. As long as you use a card >>>> and then use it to measure white balance you should be fine. >>>> >>>> On 2017-02-21 08:21 PM, Michael wrote: >>>> >>>> Well, I guess I can try to print a gray card! >>>> Anyone know what the code is for 18% gray? If 18% is right in the >>>> middle of the shades of gray I found one page ( >>>> http://www.computerhope.com/cgi-bin/htmlcolor.pl?c=808080) that says >>>> the code is: >>>> 808080 >>>> and according to the same page it is made up of equal part RGB >>>> *W3C Color Name:* Grey >>>> *RGB:* 128, 128, 128 >>>> *HSL:* 0.00, 0.00, 0.50 >>>> so what is the authoritative answer? >>>> >>>> On Tue, Feb 21, 2017 at 7:53 PM, Marcus Sundman <sund...@iki.fi> wrote: >>>> >>>>> On 21/02/17 23:16, Michael wrote: >>>>> >>>>> is there something where we can take a picture of a gray card and then >>>>>> we click on it and then dt will adjust all of the colors so that the gray >>>>>> card is >>>>>> 33-33-33%? >>>>>> >>>>> Usually you use "18% gray" meaning a card that reflects 18% of the >>>>> light in the visible spectrum and equal amounts of red, green and blue. >>>>> >>>>> It might actually be nice if the whitebalance module would support >>>>> exposure adjustment as well, to make a selected area a specific >>>>> brightness, >>>>> or what do others think? >>>>> >>>>> by the way: what is the color of the remaining 1% >>>>>> >>>>> That "33-33-33%" is your invention, so nobody but you can know what >>>>> "remaining 1%" you are talking about. If you were talking about the >>>>> reflected % of the individual color channels then there is no "remaining >>>>> 1%", but the "remaining" (absorbed) amounts of light are 67%, 67% and 67%, >>>>> respectively. >>>>> >>>>> >>>>> - Marcus >>>>> >>>>> >>>> >>>> >>>> -- >>>> :-)~MIKE~(-: >>>> >>>> ____________________________________________________________________________ >>>> darktable user mailing list to unsubscribe send a mail to >>>> darktable-user+unsubscr...@lists.darktable.org >>>> >>>> >>>> >>>> ____________________________________________________________________________ >>>> darktable user mailing list to unsubscribe send a mail to >>>> darktable-user+unsubscr...@lists.darktable.org >>>> >>> >>> >>> ____________________________________________________________________________ >>> darktable user mailing list to unsubscribe send a mail to >>> darktable-user+unsubscr...@lists.darktable.org >>> >> >> >> ____________________________________________________________________________ >> darktable user mailing list to unsubscribe send a mail to >> darktable-user+unsubscr...@lists.darktable.org >> > > > ____________________________________________________________________________ > darktable user mailing list to unsubscribe send a mail to > darktable-user+unsubscr...@lists.darktable.org > -- :-)~MIKE~(-: ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to darktable-user+unsubscr...@lists.darktable.org
