How do Photoshop blend modes work on a pixel level?

How Photoshop Blends Images

Photoshop employs blend operations on a pixel-by-pixel basis to seamlessly merge two images. Each pixel comprises multiple channels, typically red, green, and blue (RGB). The channels of corresponding pixels in the two images are blended together.

Photoshop offers a comprehensive range of blend modes, each defined by a specific blending operation. These operations can be categorized into the following families:

Normal Blending Operations

• Normal: Pixels from the first image replace the corresponding pixels in the second image.
• Lighten: Pixels from the first image brighten the corresponding pixels in the second image.
• Darken: Pixels from the first image darken the corresponding pixels in the second image.
• Multiply: Pixels from the first image are multiplied by the corresponding pixels in the second image, resulting in darker values.
• Average: Pixels from the first and second images are averaged to produce the blended pixel.
• Add: Pixels from the first and second images are added together, with values capped at 255 for each channel.
• Subtract: Pixels from the first image are subtracted from the corresponding pixels in the second image, with values floored at 0 for each channel.
• Difference: The absolute difference between pixels from the first and second images is computed for each channel.
• Negation: Pixels from the first and second images are subtracted from 255 to create a negative effect.
• Screen: Pixels from the first and second images are inverted and multiplied, resulting in brighter values.

Color Blending Operations

• Exclusion: Pixels from the first and second images are subtracted from each other, resulting in values towards the mid-range.
• Overlay: Pixels from the first and second images are layered on top of each other, with brighter or darker outcomes depending on the base pixel intensity.
• Soft Light: Pixels from the first image affect the color and contrast of pixels from the second image, producing a soft-focus effect.
• Hard Light: Pixels from the first image affect the color and contrast of pixels from the second image, producing a harder-edged effect.
• Color Dodge: Pixels from the first image brighten the corresponding pixels in the second image, enhancing contrast.
• Color Burn: Pixels from the first image darken the corresponding pixels in the second image, lowering contrast.
• Linear Dodge: Equivalent to the Add operation, but with unlimited values for each channel.
• Linear Burn: Equivalent to the Subtract operation, but with unlimited values for each channel.
• Linear Light: Combines the effects of Linear Dodge and Linear Burn, producing a more contrasted image.
• Vivid Light: Enhances the color saturation and contrast of the pixels.
• Pin Light: Makes the darker pixels darker and the brighter pixels brighter, creating a two-tone effect.
• Hard Mix: Similar to Overlay, but produces a more contrasted result.

Hue, Saturation, and Color Blending Operations

• Hue: Blends only the hue of pixels from the first image with the pixels from the second image.
• Saturation: Blends only the saturation of pixels from the first image with the pixels from the second image.
• Color (Luminosity): Blends only the color (luminance) of pixels from the first image with the pixels from the second image.

By understanding and leveraging these different blending modes, you can effectively reproduce the image blending effects seen in Photoshop in your own applications.

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