http://imagej.273.s1.nabble.com/Grayscale-values-for-RGB-images-tp3700260p3700265.html
> Dear Jacqui,
>
> in the book "Digital Imageprocessing" ("Digitale Bildverarbeitung")
> by Wilhelm Burger and Mark James Burge I read:
> "Because the subjective birghtness of red and green are much higher
> than that of blue the result would be too dark in the regions with
> a high green and red ratio if you would just use the formula (R+G
> +B)/3.
> This is why usually a weighted sum, the so called luminosity
> (freely translated from the German word "Luminanz") is used.
> In most cases (also in ImageJ) the weights used in coding the
> analog TV-color-signals are used."
>
> I also don't know how these weights were calculated, but I hope I
> could lead you into the right direction.
>
> Cheers,
> Daniel
>> Dear Karsten, Tony and Wayne,
>>
>> Thanks very much for your replies. Thanks also to Wayne for adding
>> more
>> information to the documentation.
>>
>> I'm a bit embarrassed to ask but where does the ratio for the RGB
>> conversion come from (V=0.30R+0.59G+0.11B)?
>>
>> I know that with a Bayer mask, you get twice as many "green"
>> pixels as
>> blue and red but I'm not sure how this weighting of V=0.30R+0.59G
>> +0.11B
>> has been arrived at. I did have a bit of a look around but
>> couldn't find
>> the answer.
>>
>> My images are FITC fluorescence images (mainly green) which are
>> captured
>> using an RGB camera. There is some data also in the red channel
>> because
>> of the spectrum of FITC and the use of a longpass barrier filter.
>> It is
>> a series of treated and untreated samples so they will be relative to
>> one another.
>>
>> Therefore, is it appropriate to convert them to grayscale using the
>> V=(R+G+B)/ 3 giving each channel equal weight? This is what I would
>> normally do except that now I don't actually have to include this
>> step
>> since the Measure command does it anyway.
>>
>> Or should I be using RGB weighting? If so, how should this be
>> determined
>> experimentally for the camera?
>>
>> If someone can clarify when weighting should be applied, that
>> would be
>> helpful.
>>
>> Cheers,
>>
>> Jacqui
>>
>> Jacqueline Ross
>> Biomedical Imaging Research Unit
>> School of Medical Sciences
>> Faculty of Medical & Health Sciences
>> The University of Auckland
>> Private Bag 92019
>> Auckland, NEW ZEALAND
>>
>> Tel: 64 9 373 7599 Ext 87438
>> Fax: 64 9 373 7484
>>
>>
http://www.health.auckland.ac.nz/biru/>>
>> -----Original Message-----
>> From: Rasband Wayne [mailto:
[hidden email]]
>> Sent: 15 February 2007 06:09
>> To: Jacqui Ross
>> Subject: Re: "Grayscale" values for RGB images
>>
>>> I think I must have missed an update somewhere. Usually, if I
>>> want to
>>> measure intensity of RGB images, I have to change them to grayscale
>>> first (8bit) but it seems that I don't need to include this extra
>>> step
>>
>>> now. I seem to get the same results whether I change my green
>>> image to
>>
>>> grey or not. Is this correct?
>>
>> Jacque,
>>
>> I added this paragraph to the Measure command documentation to
>> make it
>> clearer how it handles RGB images.
>>
>> "With RGB images, results are calculated using brightness values. RGB
>> pixels are converted to brightness values using the formula V=(R+G
>> +B)/
>> 3, or V=0.30R+0.59G+0.11B if "Weighted RGB Conversions" is checked in
>> Edit>Option>Conversions. The three weighting factors can be changed
>> using the setRGBWeights() macro function."
>>
>> -wayne
>
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