LAB colourmode is a good choice when converting a photograph to black and white, as it seperates the light values from the colours an image. The colours are split into 2 channels, a & b. Using LAB to sharpen means working in the LAB colour space, but with the L-channel selected, which is along side the a & b. This only sharpens the black and white information, leaving the colour pixels untouched.

In the above diagram it shows the different colour channels.




To convert an image from the RGB color mode to the Lab colour mode, we simply follow the same basic steps we used when we converted the image to Grayscale. Go up to the Image menu at the top of the screen and choose Mode (short for Colour Mode). A sub menu will appear listing all the colour modes we have to choose from in Photoshop. The mode that's currently being used will have a small checkmark beside it. To convert the image to Lab, select Lab Colour from the list:

Image > Mode > Lab Colour
You'll know that its changed to LAB when the histogram has changed from; the image on the left side to the image on the right hand side.

Nothing will seem to have happened to the image in the document window. To see the change that's taken place, we need to look in the Channels palette, which you'll find grouped in beside the Layers palette. Click on the name tabs at the top of the palettes to switch between them.

Here's what the three different channels - a Lightness channel which contains the brightness information for the image, and the two color channels "a" and "b"


By separating the lightness values from the colour in the image, the Lab colour mode has essentially created our black and white version for us. All we need to do is select it, and we can do that simply by clicking on the Lightness channel in the Channels palette. By selecting just the Lightness channel, we deselect both the "a" and "b" colour channels, hiding the colour, and leaving us with a black and white version of the photo in the document window.

Click on the Lightness channel to select it, which will deselect the two colour channels.


The Lab colour mode made it easy to select only the lightness values in the image, but all we've really done here is turned off the colour information. We need to make sure the colour is removed completely. We also need to convert the image into a more practical colour mode, one that printers and other electronic devices understand, since most won't know what to do with an image that's using Lab colour. We can solve both of these problems at once by converting the image to the Grayscale colour mode. To convert the image from Lab to Grayscale, simply go back up to the Image menu, select Mode once again, and then select Grayscale:

Convert the image to Grayscale to remove the two unwanted color channels.

Photoshop will pop open a warning box asking if you're sure you want to discard the other channels. Click OK:

Photoshop wants to make sure you don't need the colour channels before it throws them away.

Again, nothing will seem to have happened to the image in the document window, but if we look at our Channels palette, we can see that our image is now made up of a single Gray channel, just as we saw in the Grayscale tutorial, and all of the color information has been completely removed:

In Grayscale mode, images contain only a single "Gray" channel with no additional color information.


If you want to have the original colour copy of the photo, if you save the image at the point it is at, and overwrite the original saved on your computer, the colour information will be lost forever. If you want to save your black and white version without losing the original color version, be sure to select Save As from under the File menu at the top of the screen and save the black and white version under a different name.


Sharpening is something that almost any image can benefit from. Like saturation, it can easily be ignored or overdone if you’re not careful. When done right, it’s a subtle change that results in a big improvement.

It seems that there are many ways to sharpen a photo, and the most common is Photoshop’s Unsharp Mask. It’s a fine tool for most cases, but it can produce terrible results when used incorrectly or without caution.


The RGB color mode is the most common to work with, so I’ll assume that most of us use this as our default. We can still work in RGB even though we’re doing adjustments in LAB color mode, it’s just a little extra work. So open up your image as you normally would and basically process the entire image until you’re happy with it.

Sharpening should occur as the very last step in your workflow for two main reasons: 1) It’s a very localized adjustment of brightness and any further processing will exaggerate it beyond your original intent, and 2) It’s a destructive process, so we’ll be using a copy layer for the sharpening — and if you stack adjustments on top of those layers, it makes life very difficult if you choose to go back and rework the sharpening. Make a copy of the visible image by doing a “Stamp Visible” command, press Shift+Ctrl+Alt+E (Windows) or Shift+Command+Option+E (Mac OS). This gives us a single layer that contains all of the underlying adjustments we’ve applied. Now take this layer and duplicate it to a new document. Once in that new document, change the colour mode to “LAB”.

press Shift+Ctrl+Alt+E (Windows) or Shift+Command+Option+E (Mac OS)
This message will appear asking you if you want to merge and flatten the background and Layer 1. Click Flatten.


The lightness channel contains all of the light and dark tones in the image while avoiding any noise caused by the color channels. Sharpening works by darkening the darks and lightening the lights at their boundaries. Any color noise will cause noisy sharpening. In this example, I’ll show the Unsharp Mask to sharpen the image. You could use whatever method you prefer in place of that.

Switch to the channels palette and select “Lightness”. The “A” and “B” channels should be deselected and your image should look like a black and white photo. Now, apply your sharpening directly to that channel. For the Unsharp Mask, you can find it under; Filter > Sharpen > Unsharp Mask. Every image requires different settings, so don’t just assume that those numbers when you first select are the best for your image. Once you get the sharpness where you like it, apply the filter and reselect the “LAB” channel in your palette.


Created with images by moritz320 - "sharpened crayons colorful"

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