Blend modes
Encyclopedia
Blend modes in digital image editing
are used to determine how two Layers
are blended into each other. The default blend mode in most applications is simply to hide the lower layer with whatever is present in the top layer. However, as each pixel has a numerical representation, a large number of ways to blend two layers is possible.
Note that the top layer is not necessarily called a "layer" in the application. It may be applied with a painting or editing tool.
The currently most common numerical representation of colors is the one used in RGB
(red, green, blue) images, where three numbers (r, g, b) can take values between 0 and 255, each of them indicating how much red, green and blue the pixel contains. This means for example that (255, 0, 0) is intense red and (0, 0, 255) is pure blue. There are other color models, which have other number representations. For the purpose of blend modes, the principles are very similar for different color models, even though not all blend modes can be applied with all color models.
Most applications
, like Adobe Photoshop
and the GIMP
, allow the user to modify the basic blend modes - for example by applying different levels of opacity to the top picture.
has several examples of this.
is used with this blend mode, so the pictures may look grainy and harsh.
The result is a darker picture.
Formula: Result Color = (Top Color) * (Bottom Color) /255
If the two layers contain the same picture, multiply blend mode is equivalent to an exponential curve
.
If one layer contains a homogeneous colour, for example the gray color (200, 200, 200), multiply blend mode is equivalent to a curve which simply is a straight line.
For image editing it is sometimes more convenient to simply go to the curves dialog of the software, as it gives more flexibility in the shape of the curves.
The result is a brighter picture.
Formula: Result Color = 255 - [((255 - Top Color)*(255 - Bottom Color))/255]
Just like for multiply blend mode, using the curves dialog in the software sometimes is easier to use, as it increases the flexibility and control for the user.
Light parts of the picture become lighter and dark parts become darker.
An overlay with the same picture looks like an S-curve.
is also increased.
One of the main utilities for this is during the editing process, when it can be used to verify alignment of pictures with similar content.
Exclusion is a very similar blend mode with lower contrast.
Peacock will supply boolean arithmetic blend modes. These combine the binary expansion of the hexadecimal color at each pixel of two layers using boolean logic gates. The top layer's alpha controls interpolation between the lower layer's image and the combined image.
Unlike all of the previous blend modes described, which operate on each image channel independently, in each of these modes, some dimensions are taken from the bottom layer, while the remainder are taken from the top layer. Colors which end up out of gamut are brought inside by mapping along lines of constant hue and luma. This makes the operations uninvertible
– after a top layer has been applied in one of these blend modes, it is in some cases impossible to restore the appearance of the original (bottom) layer, even by applying a copy of the bottom layer in the same blend mode above both.
Because these blend modes are based on a color space which is much closer than RGB to perceptually relevant dimensions, it can be used to correct the color
of an image without altering perceived lightness
, and to manipulate lightness contrast without changing the hue or chroma. The Luminosity mode is commonly used for image sharpening
, because human vision is much more sensitive to fine-scale lightness contrast than color contrast. See Contrast (vision)
.
Few editors other than Photoshop implement this same color space for their analogs of these blend modes. Instead, they typically base their blend modes on HSV (aka HSB) or HSL. Blend modes based on HSV are typically labeled hue, saturation, and brightness. Using HSL or HSV has the advantage that most operations become invertible (at least in theory), but the disadvantage that the dimensions of HSL and HSV are not as perceptually relevant as the dimensions of the space Photoshop uses.
Image editing
Image editing encompasses the processes of altering images, whether they be digital photographs, traditional analog photographs, or illustrations. Traditional analog image editing is known as photo retouching, using tools such as an airbrush to modify photographs, or editing illustrations with any...
are used to determine how two Layers
Layers (digital image editing)
Layers are used in digital image editing to separate different elements of an image. A layer can be compared to a transparency on which imaging effects or images are applied and placed over or under an image...
are blended into each other. The default blend mode in most applications is simply to hide the lower layer with whatever is present in the top layer. However, as each pixel has a numerical representation, a large number of ways to blend two layers is possible.
Note that the top layer is not necessarily called a "layer" in the application. It may be applied with a painting or editing tool.
The currently most common numerical representation of colors is the one used in RGB
RGB color model
The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...
(red, green, blue) images, where three numbers (r, g, b) can take values between 0 and 255, each of them indicating how much red, green and blue the pixel contains. This means for example that (255, 0, 0) is intense red and (0, 0, 255) is pure blue. There are other color models, which have other number representations. For the purpose of blend modes, the principles are very similar for different color models, even though not all blend modes can be applied with all color models.
Most applications
Graphics software
In computer graphics, graphics software or image editing software is a program or collection of programs that enable a person to manipulate visual images on a computer....
, like Adobe Photoshop
Adobe Photoshop
Adobe Photoshop is a graphics editing program developed and published by Adobe Systems Incorporated.Adobe's 2003 "Creative Suite" rebranding led to Adobe Photoshop 8's renaming to Adobe Photoshop CS. Thus, Adobe Photoshop CS5 is the 12th major release of Adobe Photoshop...
and the GIMP
GIMP
GIMP is a free software raster graphics editor. It is primarily employed as an image retouching and editing tool and is freely available in versions tailored for most popular operating systems including Microsoft Windows, Apple Mac OS X, and Linux.In addition to detailed image retouching and...
, allow the user to modify the basic blend modes - for example by applying different levels of opacity to the top picture.
Normal blend mode
This is the standard blend mode which simply takes each pixel from the top layer if present. Otherwise the bottom layer is used. The article about layersLayers (digital image editing)
Layers are used in digital image editing to separate different elements of an image. A layer can be compared to a transparency on which imaging effects or images are applied and placed over or under an image...
has several examples of this.
Dissolve
The dissolve mode takes random pixels from both layers. With high opacity, most pixels are taken from the top layer. With low opacity most pixels are taken from the bottom layer. No anti-aliasingAnti-aliasing
In digital signal processing, spatial anti-aliasing is the technique of minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution...
is used with this blend mode, so the pictures may look grainy and harsh.
Multiply and Screen
Multiply and Screen blend modes are basic blend modes for darkening and lightening images respectively. There are several different combinations of them like Overlay or Soft Light (mentioned further down) and Vivid Light, Linear Light and Pin Light.Multiply
Multiply blend mode multiplies the numbers for each pixel of the top layer with the corresponding pixel for the bottom layer. As a simple multiplication for 8-bit/channel can get values as high as 65025 (255*255), which is far higher than the maximum allowed value, 255, the result is divided by 255.The result is a darker picture.
Formula: Result Color = (Top Color) * (Bottom Color) /255
If the two layers contain the same picture, multiply blend mode is equivalent to an exponential curve
Curve (tonality)
In image editing, a curve is a remapping of image tonality, specified as a function from input level to output level, used as a way to emphasize colours or other elements in a picture....
.
If one layer contains a homogeneous colour, for example the gray color (200, 200, 200), multiply blend mode is equivalent to a curve which simply is a straight line.
For image editing it is sometimes more convenient to simply go to the curves dialog of the software, as it gives more flexibility in the shape of the curves.
Screen
With Screen blend mode the values of the pixels in the two layers are negated, multiplied, and then negated again. This is in some way the opposite of multiply.The result is a brighter picture.
Formula: Result Color = 255 - [((255 - Top Color)*(255 - Bottom Color))/255]
Just like for multiply blend mode, using the curves dialog in the software sometimes is easier to use, as it increases the flexibility and control for the user.
Overlay
Overlay combines Multiply and Screen blend modes.Light parts of the picture become lighter and dark parts become darker.
An overlay with the same picture looks like an S-curve.
Soft Light
This is a softer version of Overlay. Applying pure black or white does not result in pure black or white.Hard Light
Hard Light combines Multiply and Screen blend modes. As opposed to Overlay, the contrastContrast (vision)
Contrast is the difference in visual properties that makes an object distinguishable from other objects and the background. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view...
is also increased.
Dodge and burn
Dodge and burn change the lightness of the pictures, inspired by the dodging and burning performed in a darkroom. Dodging lightens an image, while burning darkens it.- Dodge modes:
- The Screen blend mode inverts both layers, multiplies them, and then inverts that result.
- The Color Dodge blend mode divides the bottom layer by the inverted top layer. This decreases the contrast to make the bottom layer reflect the top layer: the brighter the top layer, the more its colour affects the bottom layer. Blending with white gives white. Blending with black does not change the image. This effect is similar to changing the white pointColor balanceIn photography and image processing, color balance is the global adjustment of the intensities of the colors . An important goal of this adjustment is to render specific colors – particularly neutral colors – correctly; hence, the general method is sometimes called gray balance, neutral balance,...
. The operation is not invertible. - The Linear Dodge blend mode simply sums the values in the two layers. Blending with white gives white. Blending with black does not change the image.
- Burn modes:
- The Multiply mode simply multiplies each component in the two layers.
- The Color Burn mode divides the inverted bottom layer by the top layer, and then inverts the result. This darkens the top layer increasing the contrast to reflect the colour of the bottom layer. The darker the bottom layer, the more its colour is used. Blending with white produces no difference.
- The Linear Burn mode sums the value in the two layers and subtracts 255. This is the same as inverting each layer, adding them together (as in Linear Dodge), and then inverting the result. Blending with white leaves the image unchanged.
- Hard Mix: this blend mode combines Color Dodge and Color Burn. Dodge applies to values lighter greater than middle gray, and burn to darker values.
Addition
This blend mode simply adds pixel values of one layer with the other. In case of values above 255 (in the case of RGB), white is displayed.Subtract
This blend mode simply subtracts pixel values of one layer with the other. In case of negative values, black is displayed.Difference
Difference subtracts the top layer from the bottom layer or the other way round, to always get a positive value. Blending with black produces no change, as values for all colours are 0. (The RGB value for black is 0,0,0). Blending with white inverts the picture.One of the main utilities for this is during the editing process, when it can be used to verify alignment of pictures with similar content.
Exclusion is a very similar blend mode with lower contrast.
Boolean arithmetic blend modes
Rarely, applications such as Aviary'sAviary (application suite)
Aviary is a proprietary web-based multi-media application suite that is free to use and currently under development by Worth1000. They are using the Adobe Flex platform for most of their tools...
Peacock will supply boolean arithmetic blend modes. These combine the binary expansion of the hexadecimal color at each pixel of two layers using boolean logic gates. The top layer's alpha controls interpolation between the lower layer's image and the combined image.
Hue, saturation and luminosity
Photoshop’s hue, saturation, color, and luminosity blend modes are based on a color space with dimensions that the article HSL and HSV calls hue, chroma, and luma. Note that this space is different from both HSL and HSV, and only the hue dimension is shared between the three; see that article for details.Unlike all of the previous blend modes described, which operate on each image channel independently, in each of these modes, some dimensions are taken from the bottom layer, while the remainder are taken from the top layer. Colors which end up out of gamut are brought inside by mapping along lines of constant hue and luma. This makes the operations uninvertible
Inverse function
In mathematics, an inverse function is a function that undoes another function: If an input x into the function ƒ produces an output y, then putting y into the inverse function g produces the output x, and vice versa. i.e., ƒ=y, and g=x...
– after a top layer has been applied in one of these blend modes, it is in some cases impossible to restore the appearance of the original (bottom) layer, even by applying a copy of the bottom layer in the same blend mode above both.
- The Hue blend mode preserves the luma and chroma of the bottom layer, while adopting the hue of the top layer.
- The Saturation blend mode preserves the luma and hue of the bottom layer, while adopting the chroma of the top layer.
- The Color blend mode preserves the luma of the bottom layer, while adopting the hue and chroma of the top layer.
- The Luminosity blend mode preserves the hue and chroma of the bottom layer, while adopting the luma of the top layer.
Because these blend modes are based on a color space which is much closer than RGB to perceptually relevant dimensions, it can be used to correct the color
Color balance
In photography and image processing, color balance is the global adjustment of the intensities of the colors . An important goal of this adjustment is to render specific colors – particularly neutral colors – correctly; hence, the general method is sometimes called gray balance, neutral balance,...
of an image without altering perceived lightness
Lightness (color)
Lightness is a property of a color, or a dimension of a color space, that is defined in a way to reflect the subjective brightness perception of a color for humans along a lightness–darkness axis. A color's lightness also corresponds to its amplitude.Various color models have an explicit term for...
, and to manipulate lightness contrast without changing the hue or chroma. The Luminosity mode is commonly used for image sharpening
Unsharp masking
Unsharp masking is an image manipulation technique, often available in digital image processing software.The "unsharp" of the name derives from the fact that the technique uses a blurred, or "unsharp," positive to create a "mask" of the original image...
, because human vision is much more sensitive to fine-scale lightness contrast than color contrast. See Contrast (vision)
Contrast (vision)
Contrast is the difference in visual properties that makes an object distinguishable from other objects and the background. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view...
.
Few editors other than Photoshop implement this same color space for their analogs of these blend modes. Instead, they typically base their blend modes on HSV (aka HSB) or HSL. Blend modes based on HSV are typically labeled hue, saturation, and brightness. Using HSL or HSV has the advantage that most operations become invertible (at least in theory), but the disadvantage that the dimensions of HSL and HSV are not as perceptually relevant as the dimensions of the space Photoshop uses.
See also
- Alpha compositingAlpha compositingIn computer graphics, alpha compositing is the process of combining an image with a background to create the appearance of partial or full transparency. It is often useful to render image elements in separate passes, and then combine the resulting multiple 2D images into a single, final image in a...
- Comparison of raster graphics editorsComparison of raster graphics editors- List :- General information :Basic general information about the editors: creator/company, license etc.- Operating system support :The operating systems on which the editors can run natively , meaning which operating systems have which editors specifically coded for them - List :- General...
- Digital image editing
- Raster graphicsRaster graphicsIn computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...
- Image processingImage processingIn electrical engineering and computer science, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame; the output of image processing may be either an image or, a set of characteristics or parameters related to the image...