Channel Question 1

[mscallisto]

When I convert from color to grayscale I like to change to lab color then strip the color channels, but I do have one question.

Instead of Image / Mode / GrayScale

I prefer:

Image / Mode / Lab Color
Drag the "a" channel (red-green) to the trash
Drag the Alpha2 channel to trash



Notice that after the "a" channel is trashed, the "b" channel (blue-yellow) changes to "Alpha 2"
and the Lab and Lightness channels change to "Alpha 1".

What is PhotoShop telling me, why the name change?
The Alpha 2 channel certainly seems to be the (blue yellow) channel.

 

[blueark]

You'll also notice that the color mode changes from LAB color to Multichannel. LAB color mode needs 3 channels, so if you trash one, it becomes something else.

Channels A & B contain all the color information, while L (Lightness) contains tonal values. It's quite valid to just use this channel to create grayscale.

Another way is to use the channel mixer (Image > Adjustments > Channel Mixer...) Click the 'Monochrome' box and alter the amount of information used from each existing channel. In RGB mode, you'll probably need more from the red channel than the blue, for example. Even without using monochrome, it's recommended that you increase the red channel before converting to grayscale.

 

[mscallisto]

Thanks blueark

I didn't know about the channel mixer and I'll certainly give it a try.

I do think the lab color channel strip gives better results than Image / Mode / GrayScale, at least to my eye.
Is this really true?

Could your channel mixer method be even better or is there no easy answer for these questions?

My general rule is to self evaluate the results and make a pick, but I would like to know if one method is preferred by the masters.

Thanks again

 

[blueark]

Different color modes translate to grayscale in different ways. Lab color probably gives the best results, especially if you're in a hurry, but each image is different. Channel mixing is more time consuming, especially if you're not used to it, but the advantage is that you can fine-tune the conversion process to each image.

For example, photos with a lot of red in them sometimes give disappointing results when they're just converted to grayscale. Channel mixer allows you boost weak areas and tone down areas that are too strong.

 

[mscallisto]

Thanks again blueark that helps a lot.