More Support with C*I*E LAB Color Space in version 4.1.5 (and the deal with LAB Color Space in the first place)

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The recent release of Sagelight 4.1.5 supports even more C*I*E LAB color space functionality.  The Unsharp Mask, Gaussian Blur, Tone Blender, High Pass Filter, Power Curves, Pro Quick Edit Mode, and other modes openly support C*I*E LAB channels as separate options over RGB color space, and much more is done with C*I*E LAB mode behind the scenes.

If you’ve read much of the blog or release notes, you’ll see that I mention LAB mode a lot lately.  Not just LAB mode, but C*I*E LAB mode.  I think now is a good time to write about it because Sagelight is making it more and more visible in the menu items.  The reason is because LAB mode is not always the most desirable mode, but is a mode that hobbyists, enthusiasts, and professionals want to use a lot.

As I’ve mentioned here and there Sagelight really wants to work on dual planes: to do powerful things behind the scenes so you don’t have to know what’s going on to get great results, but also to give you the power to do advanced things, if that’s what you want to do.

Sagelight has always used LAB mode behind the scenes, both C*I*E LAB mode and Hunter LAB mode (Hunter LAB is very close to C*I*E LAB mode, and has some advantages).

C*I*E LAB Color Space and Sagelight

Ok, so what’s so good about LAB Color Space, and what is LAB Coloor Space in the first place?

In a nutshell, C*I*E LAB space allows you to work with just the light in an image without affecting the color, and vice-versa. There are other modes that let you do this, but typically not with the quality and control of C*I*E LAB color space.

For example, the most common method of removing color noise is to just blur the colors without changing the light.  But, not all spaces the separate the color from the light are equal.  If you blur the colors in a non-C*I*E space, the colors can become muted very quickly.  C*I*E LAB modes keeps the colors and light as pure as possible.

Basically, C*I*E LAB Color Space is a way that you can deal with the luminance component of your image without changing the color.

Another example is to sharpen just the light without affecting the color; this allows you to avoid color edges and sparkling that can occur with sharpening.

Why don’t all editors support C*I*E LAB space?

The C*I*E LAB space calculation is very intensive, and to use it real-time and integrate it into an editor is not that easy.   A lot of editors don’t support it, or use different modes (such as YCrCb or YUV) to do calculations which do not deliver the same quality level.

C*I*E LAB vs. Other Color Spaces

The reason the term “C*I*E” is used a lot is to differentiate between C*I*E LAB color space and other color spaces such as YUV and YCrCb.

The C*I*E L channel calculation is designed to approximate the human perception of the light as closely as possible.  So, when you convert your image to black-and-white with the C*I*E color space, you’re getting the image you’d see if you didn’t see color.

I personally don’t think that a C*I*E-based grayscale image looks as perceptually as nice as just averaging the RGB image, but it does mean that Sagelight can work with the luminance and color separately and at a level that makes perceptual sense and has a very high degree of accuracy.

Each color space has a great use, but substituting YUV and YCrCB inappropriately when C*I*E LAB space should be used typically reduces the quality in your image.

Where and When to use C*I*E LAB Space in Sagelight

Sagelight supports C*I*E LAB space in many places, and there are many places where C*I*E LAB mode is used by functions within Sagelight and called another name – typically, when you see a term such as “Keep Luminance”, this means Sagelight is using C*I*E LAB Space.

Here are some good places to use C*I*E LAB mode in Sagelight

Kayak/Pro Quick Edit Mode

You can just press the labicon icon on the Kayak/Pro Quick Edit Mode and that will put Sagelight into C*I*E LAB mode.  Any function you use while in the Kayak/Pro Quick Edit Mode will be executed in C*I*E LAB mode.

Now, when you use the toning controls for color or light, these will operate on those channels individually.  If you pop up the Curves Box, the channels will now be L, A, and B, meaning you can adjust these channels by themselves.

While you’re at it, also try the hslicon icon – this will put you into HSL mode, which also has advantages.

Power Box

The Power Box can be used in the Pro Quick Edit mode and the Quick Edit Mode.

When you’re in the Power Box, try moving over to the Kayak/Pro Quick Edit Mode and using it there.  You might notice that a couple things disappear.  The Vibrance and Color Toning options disappear because they are not compatible with the C*I*E LAB mode.

The LightBlender, Definition Sliders (i.e. local contrast), and all other functions will now only operate on the C*I*E L channel. This can provide great effects and keep your image cleaner by not touching the color.

Also try this in the HSL Color Space (described above) for interesting effects.

Unsharp Mask

The Unsharp Mask in Sagelight offers three C*I*E LAB color space options.  You can sharpen all three channels in the C*I*E color space, just as you would in RGB.  This can be cleaner, but can also cause color drift.

You can sharpen just the L channel, which is a way to sharpen your image and keep color noise (i.e. sparkling) from occurring. This is generally a function used by hobbyists, enthusiasts, and professionals to keep the image quality higher.

You can also sharpen just the A & B channels. The only real reason to do that is for effect, as it doesn’t have any serious image-enhancement effect.

Gaussian Blur

The Gaussian Blur can blur on all C*I*E channels or just the L or A & B channels. The main usefulness here is to blur on the A&B channels, as this has the effect of just blurring the colors.

Blurring the A&B channels is how color noise reduction is done in most editors such as Adobe Photoshop & Lightroom.

High Pass Filter

The High Pass Filter has some interesting options for C*I*E LAB Mode.

The High Pass filter is generally used on an image prior to image blending.  It allows you flexibility in creating local contrast effects for your image.

You can perform a high pass on the RGB channels and then blend it back in for a great local contrast or sharpening effect.  Sometimes, though, you want to just use the C*I*E LAB channel.

You can do this in the High Pass Filter to keep the image cleaner and to provide different local contrast effects (through the blending).

You can also create an L-channel-only image (i.e. just black-and-white).  This has the advantage of creating an L-channel-only image that can then be used to blend just on the L-channel later, keeping the entire process only on the L channel.

Blend Undo Image

In the Blend Undo Image, you can blend two image layers together in various blend modes such as Soft Light, Hard Light, Vivid, Difference, etc.

When you select the Luminance channel, this uses only the C*I*E L channel for the blend. Similarly, if you choose the Color channels, this blends only on the C*I*E color channels (A&B).

Power Curves

The Power Curves, by far, has the most flexibility with working with different color spaces.  The Power Curves was built specifically to work with different color spaces.  It can work with XYZ, YXY, RGB, and other color spaces.

It can also work with the C*I*E LAB mode on each channel, as well as an extra Chroma channel to make the curves more useful.

C*I*E LCH space

Probably more useful than just C*I*E LAB color space, the Power Curves can also work on C*I*E LCH space, which converts the color channels into two components: Chroma (i.e. saturation) and Hue.

Try using these curves.  You can adjust the saturation, color, and light independently for some very powerful results.  In fact, this mode is so useful, this mode will either be added or replace the C*I*E LAB color space in the Pro Quick Edit Mode.

Vibrance Curves

Similar to the Power Curves, the Vibrance Curves also support C*I*E LAB color space (in the form of C*I*E LCH color space).

This creates a very stark and controllable set of vibrance functions.

Sagelight Saturation

The Sagelight Saturation modes (known as “Pro Saturation” in the menu list) provide an array of very high-quality saturation functions.

Among those is Hunter LAB, C*I*E LAB, XYZ, Sagelight Saturation, and True Color (another Sagelight algorithm).  All of these modes use C*I*E space (i.e. C*I*E XYZ, which must be converted to prior to C*I*E LAB mode) for great color control and minimum noise.

Tone Blender

The Tone Blender offers the “Keep Luminance” function that uses the Sagelight Luminance Protect feature.  This uses Sagelight RGB/C*I*E space that was developed just for Sagelight, which in turn uses C*I*E LAB as part of that space to control the light value.  This basically provides a much truer luminance than C*I*E LAB can by itself by correcting problems that can occur in C*I*E LAB space.

When Not to use C*I*E LAB Space

C*I*E LAB space is not always the best color space to use for every function.  It is an extremely useful tool to have in any editor, including Sagelight, but it is not the best at everything – otherwise it would be the only mode supported!

Here are some places where C*I*E LAB space is not always the best

Color Toning

In general, color toning is best performed in RGB space.  C*I*E LAB is not very perceptual to work with, and getting the right color and tone is just often not very possible.

C*I*E LAB is great for subtle changes here and there, but not always for overall toning.  C*I*E LAB, in this sense, is more of a “go to” set of tools, where its always worth trying, especially if you’re having some trouble getting what you want.  Sometimes it works very well and even better than RGB.

But, for general toning, it’s better to stay in the RGB space

Saturation (sometimes)

C*I*E LAB, and moreover, Hunter LAB (which is C*I*E-based) is often used for Saturation in image editors, including Sagelight (in some places).

This issue is a bit of a double-edged sword, so the following is really more of a guideline and something to think about.

C*I*E LAB is great for splitting the light and color and doing certain operations.  However, it can change the color of an image. This is because the light and colors run through two successive non-linear transformations in each direction (to C*I*E LAB and back to RGB space).  This can cause color drift.

When saturating, this typically shows as a yellowish-to-warm tone on an image.  Sometimes, this ‘warming’ effect can be nice, and since many pictures involve landscapes or are outdoors, this can be a nice extra tonal additive to your picture. 

For skin tones, though, this is sometimes not the best.

This is why Sagelight Saturation and True Color Saturation was developed for Sagelight.  In the Pro Quick Edit Mode, try switching between LAB/Perceptual mode (same thing for saturation) and True Color mode. 

Also try the Pro Saturation Mode, where you have 13 different methods to get what you’re looking for.  When it comes to adding color, its worth trying different modes, because each color space and method looks at your picture differently, and even though some methods will change the color of your image, the fact is that sometimes it just makes it look nicer because its toning your image in an aesthetic direction as it saturates, even if it isn’t technically a nice thing to do.

General Toning (most of the time)

General toning (i.e. when you’re adjusting the light properties, such as shadows, midtones, and highlights).

C*I*E LAB mode is useful for this, but only in certain circumstances.  Overall, general toning in C*I*E mode will start to make your image look artificial.

RGB mode is usually better for this, because it brings the color with it in a more natural manner, where in C*I*E LAB mode, you need to adjust the color yourself. For example, when you bring the light down in an image, you want to bring down the saturation too, and vice-versa when adding light. RGB color space does this naturally, but C*I*E LAB color space L-channel toning does not change the color, so you must deal with this yourself.

C*I*E LAB general toning (i.e. on the L channel) is useful for specific circumstances when you know this is what you want – it’s also very useful to work with bringing up shadows (it avoids noise, and generally doesn’t have the same color issues as described above).   It’s a good tool to try when you’re looking for something specific that you’re note able to get from the tools in the default RGB color space.

Conclusion

The C*I*E LAB color space is supported by Sagelight in many modes, some of which are clearly marked as choices, where other modes are behind the scenes to keep the quality of your image as high as possible.

C*I*E LAB color space is known as a way to make changes in your image that keeps the image very clean, keeping color noise from occurring by working just on the luminance channel, without changing the color.  This also lets you make color changes without affecting the light. Both have great advantages over just using RGB space.

There are some very powerful things you can do with C*I*E LAB mode, such as using the Power Curves in C*I*E LCH space (a derivative of C*I*E LAB space) or sharpening with the Unsharp Mask or the Power Box.

Always worth looking into and experimenting, it should also be considered secondary to RGB space – a “go to” color space to perform specific functions where it has specific strengths, but not really to be used as a primary editing space.

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