In this solution, we talked about the Multiply, Screen, and Overlay blend modes. They sound great, but what exactly do they do?
The Multiply blend mode takes the non-white pixels from a grayscale layer—the layer we set to Multiply—and darkens the pixels of the layers underneath. If the blend layer has white pixels, those areas are not affected. So, in this example, setting your scanline layer to Multiply allowed the photo underneath to "show through" the white stripes. By lowering the opacity of the scanline layer, we made the darkening effect more subtle. The resulting image with the scanlines is a little bit darker than the original because of the Multiply effect.
The Screen blend mode could be considered the opposite of the Multiply blend mode. In this mode, black areas in the grayscale layer—the scanline layer—allow the layers underneath to show through. Anything lighter than black will lighten the image; white areas will be displayed as white. The opacity of the Screen layer in the example at the bottom of the previous page was lowered so that the photo underneath could still show through, and, as a result, the overall image looks lighter than the original.
The Overlay blend mode is a combination of the Multiply and Screen blend modes. Areas that are less than 50% gray will give a screen effect; areas that are greater than 50% gray will give a multiply effect. Images that use the Overlay blend mode show greater contrast for this reason.
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