Blend Modes

The same old story…

Paperjs provides a number of blend modes for controlling how an effect (raster or text) is rendered onto the film sequence. The point of VOLPE is not to pre-render a film sequence, but to give as good an emulation as possible of the opening scene, so that position, size, and blending mode can be adjusted for the desired effect.

Once, however, the blend modes are produced by Paperjs, they need to be implemented as closely as possible in Imagick. And this is where the problems lay. Some Paperjs blend modes were quite easy to find in Imagick; others were completely orthogonal. Imagick has more blend modes than Paperjs, so that the formulae had to be discovered and implemented in a special version of Paperjs, VOLPaper, which is provided with this distribution .

Agreement: Paperjs blendmodes that could be implemented almost directly in Imagick

Normal

Imagick constant default.

VOLPaper	Imagick

Add

Imagick constant plus.

VOLPaper	Imagick

Color-burn

Paperjs code here was simplified by using Math.max() instead of a comparison. Imagick constant colorburn.

VOLPaper	Imagick

Color-dodge

Paperjs code here was simplified by using Math.min() instead of a comparison. Imagick constant colordodge.

VOLPaper	Imagick

Darken

Paperjs code here was simplified by using Math.min() instead of a comparison.

VOLPaper	Imagick

Difference

Paperjs code here was simplified by using Math.abs() instead of a subtraction, comparison, and multiplication.

VOLPaper	Imagick

Exclusion

Paperjs code here was simplified by using a multiplication instead of a repeated substraction.

VOLPaper	Imagick

Hard-light

Imagick constant hardlight.

VOLPaper	Imagick

Lighten

Paperjs code here was simplified by using Math.max() instead of a comparison.

VOLPaper	Imagick

Multiply

VOLPaper	Imagick

Minus

VOLPaper	Imagick

Overlay

VOLPaper	Imagick

Screen

VOLPaper	Imagick

Soft-light

Imagick constant softlight.

VOLPaper	Imagick

Where Imagick fails: Copying opacity

In a number of cases, Imagick produces very strange results where the overlaid image spills over into the translucent space. This could be remedied by copying the opacity channel onto the final image.

Colorize	Hue	Luminize	Saturate

Color

Imagick constant colorize.

VOLPaper	Imagick

Hue

VOLPaper	Imagick

Luminosity

Imagick constant luminize.

VOLPaper	Imagick

Saturation

Imagick constant saturate.

VOLPaper	Imagick

Imagick blend modes that were added to VOLPaper

Divide

VOLPaper	Imagick

Divide-src

This required copying opacity. Imagick constant dividesrc.

VOLPaper	Imagick	w/o opacity copying

Linear-burn

Imagick constant linearburn.

VOLPaper	Imagick

Linear-light

Imagick constant linearlight.

VOLPaper	Imagick

Pegtop-light

Imagick constant pegtoplight.

VOLPaper	Imagick

Pin-light

Imagick constant pinlight.

VOLPaper	Imagick

Vivid-light

This required copying opacity. Imagick constant vividlight.

VOLPaper	Imagick	w/o opacity copying

Darken-intensity

This required copying opacity. Imagick constant darkenintensity.

VOLPaper	Imagick	w/o opacity copying

Lighten-intensity

Imagick constant lightenintensity.

VOLPaper	Imagick

Blend modes added to both Imagick and VOLPaper

Grain-extract

Imagick constant mathematics with corresponding formula.

VOLPaper	Imagick

Grain-extract-src

Imagick constant mathematics with corresponding formula.

VOLPaper	Imagick

Grain-merge

Imagick constant mathematics with corresponding formula.

VOLPaper	Imagick

Divide-intensity

This required copying opacity.

VOLPaper	Imagick	w/o opacity copying

Multiply-intensity

VOLPaper	Imagick

Negation-src

VOLPaper	Imagick

Negation-sum

VOLPaper	Imagick

Overlay-intensity

VOLPaper	Imagick

Overlay-intensity-src

VOLPaper	Imagick

Screen-intensity

VOLPaper	Imagick

Screen-intensity-src

VOLPaper	Imagick

Blend mode that failed to produce anything reasonable in Paperjs

Negate

PaperJS original	VOLPaper	Imagick

Blend mode that failed to produce anything reasonable in Imagick

Subtract

The use of the subtract constant resulted in an unusable image which was identical to the result produced by modulussubtract, but minussrc worked as intended.

VOLPaper	Imagick	Imagick original

Blend mode that produced insufficient agreement between Imagick and Paperjs and was not implemented

Hard-mix

VOLPaper	Imagick

Notes

1. While results are not 100% identical, care has been taken to achieve an effect that is as near as dammit. Images can be overlaid with grain extract to determine any deviations, but keep in mind that Paperjs's pixel positions are rarely integers, and minor differences will be found. Also, as I have complained to the makers of Paperjs, Paperjs applies an undetermined gamma to all images, brightening them in the mid ranges by about 5%.
2. "Intensity" modes are based on a gray-scaling according to the rec601luma formula (0.299/0.587/0.114 for RGB).
3. "Src" modes are analogous to Imagick's "SRC" modes in defining source and destination images.
4. All Imagick constants require a leading string "imagick::COMPOSITE_".
5. Blend modes that were not used are all the Duff-Porter modes (destination_*, source_*) and average (since this can be emulated by "normal" and setting the opacity to 0.50).