Ned writes ...
> >From: Todd Flashner <[EMAIL PROTECTED]>
>
> >However, for a neutral gray they (RGB) SHOULD all be
> > the same number.
>
> no, total rubbish ... the profile defines the relationship
> between the value and the actual colour output
Quite right, but we're talking about typical
- Original Message -
From: "Ned Nurk" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Sunday, November 11, 2001 11:36 PM
Subject: Re: filmscanners: creating correction curves from scanned
calibration chart?
>
>
>
> >From: John Brownlow <[EMA
> RGB values mean diddly squat.
> They are just a measurement of the amount of current in a scanner
> ccd
Only if it is a raw scan. A typical scan has the data setpointed and
tonally adjusted. That means that 0 IS the darkest value in the resultant
file, and 255 IS the lightest value in the fi
I've come of retirement for this one :-)
>From: Todd Flashner <[EMAIL PROTECTED]>
>However, for a neutral gray
>they (RGB) SHOULD all be the same number.
no, total rubbish. the profile defines the relationship between the value
and the actual colour output. Profiles do NOT attempt to balance
shAf called me, lol)
>From: "Austin Franklin" <[EMAIL PROTECTED]>
>Reply-To: [EMAIL PROTECTED]
>To: <[EMAIL PROTECTED]>
>Subject: RE: filmscanners: creating correction curves from scanned
>calibration chart?
>Date: Sun, 11 Nov 2001 14:54:01 -0500
>
>From: John Brownlow <[EMAIL PROTECTED]>
>this is nuts. loads of people, me included, edit by the numbers. The whole
>point of an ICM profile is so that the same RGB values display the same on
>different profiled devices.
Sorry to tell you, but you are *so* wrong. RGB values mean diddly squat.
>> If you're using PS, click on each the points in the image that
>> I think if you control-shift-click on each point it will set
>> those points on the individual channel curve line.
>> ...
>
> Control-clikking a region in the image allows me to manually set the curve
>... for each RGB channel .
Maris writes ...
> If you're using PS, click on each the points in the image that
> you want to set, check the read numbers, then click, ...
Bob writes ...
> I think if you control-shift-click on each point it will set
> those points on the individual channel curve line.
> ...
Control-clikki
Ned writes ...
> >From: "michael shaffer" <[EMAIL PROTECTED]>
> > Because my system is calibrated, I am not assuming. If
> >my monitor is truely gamma calibrated, and I use a gamma=2.2
> >working color space, then a 18% gray card's RGB value should
> >be R=G=B=117aren't mine). ...
>
> your as
> your assumption being that 0,0,0 is totally black and 255,255,255
> is totally
> white in that 2.2 gamma colour space. Would be a pretty daft
> colour space as
> you can't get either on a monitor or printer and so you end up wasting a
> whole bunch of values that could never be properly exp
>If you're using PS, click on each the points in the image that you want to set, check
>the read numbers, then click, in the separate channels, on the curve at or about that
>point, they type in the read number in the input box and your desired output number
>in the output box. Do this for eac
>From: "michael shaffer" <[EMAIL PROTECTED]>
> Because my system is calibrated, I am not assuming. If my monitor is
>truely gamma calibrated, and I use a gamma=2.2 working color space, then a
>18% gray card's RGB value should be R=G=B=117 (see formulas below, they
>aren't mine). I ask you ...
MAIL PROTECTED]>
Sent: Sunday, November 11, 2001 7:59 AM
Subject: RE: filmscanners: creating correction curves from scanned calibration chart?
[snippped]
| However, I'll probably satisfy myself having gray balanced (as Bruce
| Fraser implies ... "you're 95% there if the grays
Ned writes ...
> There is a problem here, and that is your assumption
> that the 18% grey would be at RGB 117/117/117.
> ... The correct value for mid grey would be... whatever the RGB
> value you have measured off your monitor that matches mid grey. ...
> ...
> Basically - the only way to do th
head.
Regards
Ned
>From: "michael shaffer" <[EMAIL PROTECTED]>
>Reply-To: [EMAIL PROTECTED]
>To: "film scanner list" <[EMAIL PROTECTED]>
>Subject: filmscanners: creating correction curves from scanned calibration
>chart?
>Date: Fri, 9 Nov 2001
I have a scan of a photographed color chart, and I also have the logD
reflectance values for the patchs. I want to create Photoshop curves for
correcting the scan ... for example, assuming gamma=2.2 working space, I
calculate a value of 117 for 18% reflectance:
gray_value == (0.18^(1/2.2))*255 =
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