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Why Use Greyscale?

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  • Why Use Greyscale?

    I am new at photo restoration but sincerely trying to learn the art and skills of photo manipulation.
    I notice a lot of individuals convert color and b&w images to greyscale before making adjustments. I am confused about this operation. What is the advantage and why do many individuals make this adjustment before applying enhancements?


  • #2
    I can't for the life of me think of one good reason to convert to greyscale.
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    • #3
      If I want to change a color photo to a black and white photo I make use of the grayscale. It gives me a much better black and white photo.

      I change the RGB Image to a LAB color photo. I then click on the LAB b channel and drag it to the trash, this allows photoshop to change the remaining two channels to Alpha 1 (lightness) and Alpha 2 (LAB a). Then click on the Alpha 2 channel and drag it to the trash leaving only the Alpha 1 (lightness) channel.

      The Alpha 1 (Lightness) channel describes the brightness of the pixels from dark to light, and will give you a perfect grayscale image.

      Select Image menu and choose Grayscale from the fly out and you now have a grayscale image containing the correct amount of highlights and shadows.

      Take a color image, convert it first to grayscale using image mode, save it, then open the original color image back up and convert it using the above process. Get both images opened on the monitor at the same time and I believe you will immediately see the difference in the two images.



      • #4
        There are quite a few methods for getting a good greyscale image from a color image, but I don't think that was the question. I believe he was asking when would be an appropriate situation where converting to greyscale (grayscale?) mode would be advisable.
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        • #5
          When converting a color image to a black and white.


          • #6
            I can't think of any reason to convert to greyscale either, unless you want a B&W photo, and then I'll usually use the channel mixer so I have more control.

            Sometimes, I'll make adjustments to only one channel (which show as greyscale onscreen....could that be what you mean, John?

            As far as converting to greyscale for any other reason? Can't think of any.


            • #7
              I guess I'm being too subtle:

              Converting over to Greyscale mode is a destructive, irreversible, and needlessly clumsy method of viewing your image as b/w. There are many preferable methods that will preserve the original data, and simultaneously provide greater control over the process.
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              • #8

                I'm definitely a newbie when it comes to photo restoration, so I'll ask the dumb question. (Actually, my fiancee does all the restoration, I just look throughout the net to try to find "tools" to help her along)

                Doug, you mentioned in your last post that simply taking a photo and converting it to greyscale is a "needlessly clumsy" method. I was wondering if you could elaborate on a more "preferred" method of obtaining the same result.
                Last edited by admin_fff; 03-20-2002, 04:41 PM.


                • #9
                  A couple of excellent methods were mentioned up above ^^^, including my personal favorite, channel mixer.

                  In many cases, the decision is taken out of our hands when scanning b/w originals. Usually one of the channels is so much better than the other two there's no real reason to keep them around.

                  My favorite short-term method is simply a hue/sat adjustment layer with saturation turned all the way down. This leaves the original untouched, and still lets you have your b/w image.

                  The most important things are to not discard data before you're positive it won't be needed, ever, and to engage brain instead of trusting any of the 'auto' controls.

                  Plus gs mode is only one 8-bit color channel, which will necessitate conversion right back to RGB for many operations.
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                  • #10

                    Thanks for the response. I should have read George's post a little more carefully. I'll have to give that method a try.


                    • #11
                      The method in a previous post probably gives more control than you really want to have. Here's the link:



                      • #12
                        With the B& W conv. from color. You have to think of brightness(luminosity). Than Hue or saturation. Your better to color correct the image first, for B&W conv. to grayscale. You have to look in your channels( do channel blending) for the best one(s) to use, for the channel mixer,apply image,calculations.
                        You have to remember one thing. During the conversion(with A.P.S.), the green is twice important as the red and six times important then the blue channel.That's why I like the "apply image command",you can blend rgb and/or cmyk channels. You can cross color spaces. Target thr green channel to mix into. Doing the Lab conv. and deleting the "a" and "b" channels is nothing more then,just using the "green" channel of rgb. But bottom line you have to look in your channels to see whats going on. And not the historgram.


                        • #13
                          Your color images, will look funky(doing the channel blending) before you convert them to b&w. But that does not matter. As long as you get a better b&w from it.

                          Let me correct this: I said:

                          <Your better to color correct the image first, for B&W conv. to grayscale. >

                          Your better to color correct the image first,using channel blending(targeting the best channels to use) then convert to b&w. The channel mixer, calculations,apply image command do the same thing in reference to channel blending. Depends on how you want to approach it.
                          Also, if your a Swashbuckling type. Take a stab at cmyk with the image and use the "black" channel for blending. Tooshay !!!

                          Last edited by john_opitz; 03-21-2002, 10:19 AM.


                          • #14

                            Thanks for the detailed replies. I will have to pass on the info to the little lady. I know just enough about Photoshop to be dangerous.

                            Thanks again



                            • #15
                              You're welcome David. I'm in the same category you are when it comes to Photoshop. I'm always in trouble.



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