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greyscale/RGB convert V.S. Color Channels (monochrome)


C

cjogo

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Have been taking extra time to use the channel mixer (checking-monochrome)and select each band's percentage ...to acheive a neutral B&W. Recently I have been skipping the procedure and a the end of all performances simply converting to greyscale and then direclty back to RGb....any loss of quality using this procedure? My lab only accepts RGB TIff files ( we are scanning B&W film and transferring them to our lab for analog printing)


http://fp2k.redshift.com/cjogo/gallery_fine_art.htm
 
I took the liberty to move this thread to the photography forum. Hope you don't mind...

The most correct greyscale you can get is by switching to lab mode, and then selecting the Lightness channel.

When you use Desaturate or Greyscale, PS itself calculates mean values based on the data from your three channels R,G and B. As the algorithm used is set to specific probable relationships of hues, this can be ok, but often is not as good as using Lab lightness.

The method you used previously, using the ChannelMixer is the one I like most as it offers ways of tweaking, yet there's also a danger: when the total sum does not add up to 300%, the file can become either lighter or darker.

A good procedure is to use the ChannelMixer but as an adjustment layer.

You can even, to enhance some colour hues for example add a ChannelMixer adjustment layer and still tweak the original image with, say, ColorBalance. For some effects, this can be great as you can get effects that come close to using red, yellow, blue etc filters on your lens.
 
Yeah... that's what I said...

Someone should merge these threads. heh

Good thought about using adjustment layers Erik... I totally zoned on that. You could just move the layer into each document you needed changed.
 
I wanted to merge both threads, but unfortunately the option to do so seems to have disappeared.

As for the AdjLayers: I've been doing quite some work switching to greyscale, so it's fresh in my memory.
Good idea to move the doc. And also good idea to create an action (I usually forget this great option!)
 
"The most correct greyscale you can get is by switching to lab mode, and then selecting the Lightness channel."
After Lab mode is the file still in RGB? We already spend 5 hours/4 days a week-- scanning for the last 5 years..maybe we should create an action. A image takes an average 1/2 hour min to create (4800 dpi about 20+min for the scan alone) ..SO naturally we are trying to find ways to save time. :} The galleries keep selling so we have to continue producing.
 
Cie LAB is the largest mode. All other modes can only display/contain a subset of data from LAB.
So changing from RGB to LAB is no problem as LAB can easily keep all information, and swithcing back is ok also.
(for example switching from RGB to CMYK and then back would in most cases mean a loss of data).

But RGB isn't RGB as there are several RGB's. Adobe RGB is best for print as in includes more hues than a monitor can display.
My monitor can display sRGB which is about the maximum a monitor can nowadays, but Adobe RGB contains more data.

For future scans, I suggest you may want to scan directly in LAB mode, 16bit (more hues) and then apply the action I add here.
PLEASE test it out before you use it on vital data!!!!!


It changes a LAB 16bit file to 8bit, deletes the a and b channel (once a is gone, b is called alpha2), then changes the lightness channel to greyscale, and then to RGB mode. The greyscale step is necessary and can do no harm asthere is only one channel left.

It is inside a folder called "photo" that you may rename, but in which you can keep similar actions. Should you already have one, or some, you can simply drag them into another folder in the actions palette. Don't forget to click on the arrow at the upper right-hand side of the pallette and then save your action(s).

enjoy!

and...good to hear you're doing business!
 
Great tip guys!

Erik,

I downloaded and tried your photo action. Worked like a charm. I love it. Thanks.

As always - you impress me with your knowledge on the subject of photography!
 
I downloaded and was unable to perform the action--or locate--is just shows a ATN file and nothing activates??
 
Did you unzip it to the correct folder? On win XP: Program Files>Adobe>Photoshop 7.0>Presets>Photoshop Actions

and then, on the Actions Palette, did you open the menu with the small arrow up right and chose to load this atn(actions) file?

It should work...
 
Sure helps with instructions!!!

thanks for that WIN tutorial~~~~~~~~~ :righton:
 
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