How does Photoshop Blend Two Images?

Photoshop blends two images by performing pixel-by-pixel operations that combine the corresponding pixels from each image based on a specified blend mode. Blend modes determine how the colors and channels of the two images are combined to create the resulting pixel.

RGB Channel Blending

For RGB images, Photoshop uses the following macros to blend channels:

• ChannelBlend_Normal: Blends pixels using the standard blending algorithm.
• ChannelBlend_Lighten: Blends pixels to create a brighter result.
• ChannelBlend_Darken: Blends pixels to create a darker result.
• ChannelBlend_Multiply: Multiplies the channels of the two pixels, often darkening the result.
• ChannelBlend_Average: Averages the channels of the two pixels.
• Other blend modes include Add, Subtract, Difference, Negation, Screen, Exclusion, Overlay, SoftLight, HardLight, ColorDodge, ColorBurn, LinearDodge, LinearBurn, LinearLight, VividLight, PinLight, HardMix, Reflect, Glow, Phoenix, and Alpha.

Buffer-Based Blending

To simplify blending, Photoshop uses buffer-based macros for RGB color blending:

• ColorBlend_Normal: Performs normal blending.
• Other blend modes include Lighten, Darken, Multiply, Average, Add, Subtract, Difference, Negation, Screen, Exclusion, Overlay, SoftLight, HardLight, ColorDodge, ColorBurn, LinearDodge, LinearBurn, LinearLight, VividLight, PinLight, HardMix, Reflect, Glow, Phoenix.

HLS-Based Blending

некоторых blend modes in Photoshop involve converting the RGB channels to Hue, Saturation, and Luminance (HLS) and back again. These macros facilitate HLS blending:

• ColorBlend_Hue: Blends based on hue.
• ColorBlend_Saturation: Blends based on saturation.
• ColorBlend_Color: Blends based on color.
• ColorBlend_Luminosity: Blends based on luminosity.

Example

To blend two RGB images, you can use the following code:

ColorBlend_Glow(TargetPtr, ImageAPtr, ImageBPtr);

Resources

For further information, refer to the following resources:

• PegTop blend modes
• Forensic Photoshop
• Insight into Photoshop 7.0 Blend Modes
• SF - Basics - Blending Modes
• finish the blend modes
• Romz blog
• ReactOS RGB-HLS conversion functions