black & white


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jywong

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Jul 27, 2005
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#1
which way of colour image convert to black and white?
1.desaturation
2.grayscale
3.channel mix
4.lab
5.????
 

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Phildate

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#2
Personally I either use Channel Mixer or I desaturate in Adobe Raw. Using Greyscale is the worst way as it reduces each picture to 8 shades of white/grey/black, compared to 256 if you use Desaturate or Channel Mixer.
 

ortega

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Nov 2, 2004
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#4
Phildate said:
Personally I either use Channel Mixer or I desaturate in Adobe Raw. Using Greyscale is the worst way as it reduces each picture to 8 shades of white/grey/black, compared to 256 if you use Desaturate or Channel Mixer.
correct me if i am wrong but greyscale reduces the image to 100 levels of black from 0% to 100%
 

Jan 23, 2005
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#5
ortega said:
correct me if i am wrong but greyscale reduces the image to 100 levels of black from 0% to 100%
There is no reason why "grayscale" shouldn't give the full bit depth. From a 24 bpp image, this could actually be more than 8bpp/256 levels of gray, although most software rounds it off to 8 bpp.

The problem with the "different" methods is that they may not be different at all. "Grayscale" is a very unspecific function, and in some software, "grayscale" and "desaturate" are actually the same. Desaturation in turn is also not a well defined method as long as the colour model/colour space isn't given. The "LAB" method is nothing else but desaturation, except that it occurs in a defined colour space - LAB.

"Channel mixing" is a very generic procedure with multiple free parameters. As such it is more of a "filter effect" tool than a specific method for converting to grayscale.

For plain vanilla JPEG images, the most effective method is to simply remove the chrominance components from the file (common JPEG stores images in a YCrCb colour model), without the need for image processing software. Since the luminance (Y) in the YCC colour space is close to the apparent brightness of different colours, the resulting grayscale image usually looks very natural.
 

jywong

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#6
your got detect if use diierent w.balance at raw to convert b&w is diffrent?.
let say you use around 6500k(warm),you can found red channel is more bright,but also most blur,blue is most dark,but it is more sharp... if u use around 2350k(cold),is totally reverse with 6500k..so if use channel mix,i use diffrent way to convert it...normally is red +,green+,blue-,but it not suit for all w.balance....
 

ptwong

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Nov 10, 2003
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#7
desaturation is worse but easiest.
channel mixer is great but more tedious.
I think standardising the wb would help during the process instead of AWB.
I use an PS action that i downloaded which just requires me to change the inputs.
 

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