Convert Color to Grayscale

[sanking]

Most people appear to find that the convert to grayscale feature in Photoshop CS3 gives better results than the desaturate command. A short article in the current issue of Photo Techniques provides some interesting information about why this is so.

However, if one knew in advance that they wanted a grayscale file from a color negative or transparency, why not just scan the color material in grayscale? Has anyone actually compared results using the two methodologies and discussed pros and cons?

Sandy King

[Ed Richards]

You lose the ability to apply controls during the coversion - think of it this way: messing with the CS3 black and white conversion is like applying colored filters when shooting black and white film. Why give that up by scanning directly to grayscale?

[David Luttmann]

However, if one knew in advance that they wanted a grayscale file from a color negative or transparency, why not just scan the color material in grayscale? Has anyone actually compared results using the two methodologies and discussed pros and cons?

Sandy King

Sandy,

You have an immense amount of control over how the greyscale image will appear if you scan in RGB and then make your adjustments after the fact. There are numerous methods of finding the desired spectral response by using the channel mixer on the RBG file and then selecting monochrome at the bottom.

A perfect example of this is using color film and then creating what B&W film effect you’d like using the channel mixer and curves in RBG and the monochrome. I’ve made actions that can mimic Tri-X, HP5, FP4, Pan F and Fortepan 400 from color film or digital files that have been calibrated.

Once you scan in greyscale, you’re done. There is nothing you can do to change your spectral response curve.

[Martin Miksch]

The most controll you get using channel mixer in PS.
Regards
Martin

edit

[Ken Lee]

In CS 3, there is a tool called Black & White. which has more sliders than the Channel Mixer. It gives greater specificity and control. It was designed for this purpose.

When used as a Luminosity correction, it allows you to control color intensity in a remarkable way.

Don't take my word for it: You really have to watch one of the online tutorials to see how effective this tool can be.

[sanking]

In CS 3, there is a tool called Black & White. which has more sliders than the Channel Mixer. It gives greater specificity and control. It was designed for this purpose.

When used as a Luminosity correction, it allows you to control color intensity in a remarkable way.

Don't take my word for it: You really have to watch one of the online tutorials to see how effective this tool can be.

I actually was using the Black and White tool this afternoon and it is quite remarkable. In fact, it was using that tool that led me to post the question. Everything that has been said suggests that it is better to scan in color and then convert to grayscale, by whatever method, in Photoshop. But is this a 100% slam dunk, or is there anything that might favor a direct grayscale scan?

Sandy King

[Ed Richards]

> is there anything that might favor a direct grayscale scan?

Lack of memory to handle the much larger RGB file.

[David Luttmann]

File size...that's about it.

[Ken Lee]

"Once you scan in greyscale, you’re done. There is nothing you can do to change your spectral response curve."

Perfect !

"is there anything that might favor a direct grayscale scan?"

It depends on your scanner. Some RGB sensors have their best resolution in the Green channel. On the other hand, if we toss out the other channels, this amounts to shooting through a green filter: not always the desired effect.

Perhaps there is no hard-and-fast rule. It depends on what you are trying to accomplish. Resolution being only one of several factors.

If memory were no consideration, I would (and do) scan and save in 48-bit RGB, keeping the image that way until print time. I would perform desaturation as a layer, or layers (since more than one B&W layer in PS can be applied, to taste).

There is really no need to convert to Greyscale, but if you want to send a smaller file over the wire to the printer, then you can convert before printing.

I really don't know whose logic is best to convert to 8-bit Greyscale (Photoshop or the printer driver). If I had to guess, it would be Photoshop.

[Ted Harris]

For portraits and figure work use of the CS3 B&W tool also gives you tremendous flexibility in adjusting skin tones, blemishes, etc.