Layer Blending Modes in Gimp

October 29, 2009

In a lot of the tutorials I’ve done so far, I’ve had you change the blend mode of layers – we’ve used overlay quite a bit, for instance.

There’s a number of different layer blend modes and I’m going to do my best to explain them all here. I do not consider myself an expert. I’m just showing you examples, and telling you my intepretation of them. I may not always be 100% accurate with what is actually happening behind the scenes.

First, here’s the image that I will use as my bottom layer:

Katie

Say hello and Thank You to my beautiful oldest niece for helping us demonstrate layer blend modes.

The top layer I’ll be using looks like this:

In all the examples shown below, hover over the image in order to see the effect. Also, all these layer modes actually have a mathematical formula that’s used to create the effect. Personally, I don’t care about the formula, I just want to know what it looks like. If you do care about the formulas, please read about the Gimp Layer Modes here.

Normal: The first, and default, layer mode is Normal. Normal means that whatever layer is on top is what you’re going to see. So, in our case, if we set the layer mode to normal, and opacity at 100% we’re going to see the above striped image.

Dissolve: Dissolve is going to pick a percentage of random pixels from the top layer and replace them with pixels from the bottom layer. The percentage is determined by your opacity. If your opacity is 100%, no pixes will be replaced. If your opacity is 90%, 10% of the pixels will be replaced, all the way down to a 0% opacity meaning you can see the entire bottom image. To see the results of this layer mode, hover over the image below (be patient, it might not load right away) to see the same image with my top striped layer set to Dissolve and 50% opacity:

Multiply: Think of every color in your image having three mathematical values associated with it: one that represents how much red is in it, one that represents the green, and one that represents the blue. And every color can be made up of some combination of these numbers, and the highest each can go is 255. So (255, 0, 0) means it’s pure red. (0, 0, 0) is pure black and (255, 255, 255) is pure white.

What Multiply does is take the values of your top layer and multiply them by the values in the lower layer, and divide the resulting number by 255. Because black is (0, 0, 0) and multiplying by 0 always gives you 0, using Multiply with pure black is going to keep the image at pure black. Because white is all 255 and multiplying by 255 and then dividing by 255 gives you the same number you started off with – using Multiply with a white layer does nothing.

So, the short version is: Multiply makes everything darker, except when multiplying with white, which basically turns transparent. Hover over the image to see the effect of the top layer being set to Multiply (at 100% opacity):

Divide: I’m sure you’re shocked to here that, mathematically, this is basically the opposite of Multiply. What you really need to know is that white will still be transparent, and black will turn to white instead of staying black … and colors will have the opposite effect as they did in multiply. In multiply, the red patch made my nieces face redder, and in divide, it’s going to make it bluer. Hover to see what the layer looks like set to Divide:

Screen: I do not understand the mathemetics behind Screen. All I know is that black becomes transparent, white becomes pure white, and everything else just gets lighter. So, basically, the lighter the color in the layer, the lighter the final image will be:

Overlay: This is the blend mode I probably use most often. Overlay is basically a combination of Multiply and Screen, but not as extreme – overlay the photo with something dark and it makes it darker (but even pure black won’t turn it to pure black), overlay with something light and it makes it lighter:

Dodge: While this (obviously) isn’t technically accurate, I’ve always thought of Dodge as a “Screen on Acid” mode. It results in a really intense, brighter image:

Burn: And Burn is like Multiply on acid – the image gets darker and has more contrast:

Hard Light: Usually this reminds me of Overlay, but with my extreme colors here (pure black and white) it looks completely different. Remember, with Overlay, pure black and pure white just darkened a lot and lightened a lot. With Hard Light, pure black will turn the image pure black, and pure white will turn it pure white. Hard Light actually uses a different formula for darker colors than the lighter colors, so, it kinda makes it like Overlay on acid – very extreme results for the extreme ends of the spectrum (like pure black remaining pure black):

Soft Light: Soft Light and Overlay always look exactly the same to me. I guess in some versions of Gimp it actually is the same:

Grain Extract: I don’t understand Grain Extract, what it does, or what it’s for. It seems to be like divide in that it does the whole “opposite” thing – but really to an extreme. I’ll just show you the example and move on:

Grain Merge: The only thing I can say about Grain Merge is that it seems to be the opposite of Grain Extract:

Difference: Difference is cool. Remember how all colors have a mathematical value? Difference just shows you the difference between the value of the two layers. Since black is all 0s, using difference with pure black shows no difference at all. The rest just looks odd:

Addition: I bet you can guess both the math behind this one AND what using pure black will do – we’re adding the two layers together – this means, since pure black is all zeros, it has no effect. Since white is the highest value, if you add anything to it, it can’t get any higher, so using addition with a white layer will turn the image all white. Anything else just makes it lighter:

Subtract: I know this sounds like it’s the same as difference – but difference was the absolute value of the difference between the two layers, and you’d get the same result no matter which layer was on top. with Subtract, it’s subtracting the top layer from the bottom layer. Anything that goes into a negative number will just be set to 0 – which is going to result in a lot more darker spots on your photo (no change when subtracting pure black, since it’s still all 0s, and subtracting pure white – the highest value – is going to result in pure black):

Darken Only: Looks at the values for each pixel in each layer and determines which one is darker and uses the darker value – Darkening with pure white will have no affect, darkening with pure black will always turn the image black:

Lighten Only: Opposite of Darken Only:

Hue: This changes the hue of the lower layer to that of the upper layer. Since Black, white and pure shades of gray have no hue, those have no affect on the image:

Saturation: This changes the saturation of the lower layer to that of the upper layer. For blacks, whites and grays, this desaturates the image:

Color:This changes the hue and saturation of the lower layer to that of the top layer. When using a solid color (black, red, blue, whatever) I think of it as making a monotone image, with whatever color you used:

Value: Value is just… crazy, man. According to the gimp site (linked to way up there) “Value mode uses the value of the upper layer and the saturation and hue of the lower layer to form the resulting image. You can use this mode to reveal details in dark and light areas of an image without changing the saturation.” I don’t know WHAT that means. But this is what it looks like:

If any of you can provide more insight on some of the blend modes (especially the two grain ones!), feel free to do so in the comments!

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Filed under: Photo Editing
  • Belle

    Great tutorial! Thanks very much.

  • Name

    Really enjoying your blog, and this was a very informative post. Thanks!

  • Snaphappy

    I'm Learning...keep it up iffles...I like your work.

  • Meginsanity

    That was fascinating! Thanks for the overview. Now I have a better idea of what I'm doing.

  • Thin Smek

    Lovely work, but I find the hover thing is terrible. I have to wait like a minute with my mouse over your niece each time before I can get any results. I think just placing the before and after images would work better. I had to give up before I was halfway through! (I am using Google Chrome to view)
    Thanks for all the hard work you've done though.

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