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View Full Version : So, how does the "Multiply" blend mode work, anyway?



Captain Obvious
06-11-2007, 07:47 AM
In the classic texture editor, that is. If you have a texture, and then add another one on top and set it to "Multiply," it doesn't actually multiply the colour values. If you set it to "PShop Multiply," it works as you'd expect it to. What's the logic behind the normal "Multiply" mode?

ingo
06-11-2007, 09:10 AM
Yes, Photoshops multiply is a bit odd. As far as i remember PSs multiply multiplies all channels (h,s,b) while LW multiplies only the hue and the saturation, which is the more natural thing. Otherwise you mostly end up with an image with colors from light black to dark black.

Captain Obvious
06-11-2007, 09:44 AM
Then why does multiplying something by white (255/255/255 in RGB) actually INCREASE the brightness of it? At any rate, the most logical thing would be to multiply the RGB values separately. Blue multiplied with gray equals darker blue. White multiplied by white equals white. And so on.

Mike_RB
06-11-2007, 10:34 AM
its a compositing multiply. Its just math. It's actually multiplys the values, which means the result generally gets bigger.

Captain Obvious
06-11-2007, 10:43 AM
Values in what space? Surely it can't multiply the raw integer values (0-255), and if it used 0-1, multiplying by 1 wouldn't make things brighter.

Weetos
06-11-2007, 11:06 AM
Values in what space? Surely it can't multiply the raw integer values (0-255), and if it used 0-1, multiplying by 1 wouldn't make things brighter.

Ha. That's what I always wondered. A 0-1 range would allow to use a multiply function without over exposing, as you suggest, which would be imho much easier to use. That would make much more sense

gerry_g
06-11-2007, 12:56 PM
In Photoshop at least, Multiply takes the values of the layer that sits directly below the one you are applying it to and uses the values of that layer to multiply the current layer, so where the lower layer is darker the top layer gets darker by a multiple and where it is lighter the reverse, Photoshop only uses 'value' in the lower layer and yes it works on 0-255, meaning it blows out the whites and bogs in the blacks.

toonafish
06-11-2007, 03:38 PM
daja vu....

http://www.newtek.com/forums/showthread.php?t=36585&highlight=multiply

:D

Captain Obvious
06-11-2007, 06:19 PM
No answer back then, either? Arrrrgh.

toonafish
06-12-2007, 01:51 AM
I reported this as a bug then, and with the next (9.0) update we got the new Pshop modes. So I suppose these were the fixes for the old layer modes, and the old ones were kept to be backwards compatible.

Captain Obvious
06-12-2007, 03:43 AM
Weren't the PShop modes a feature introduced with 8.5?

anieves
06-12-2007, 09:33 PM
yes the Photoshop blending modes were introduced in v9; they appear in the list as "PShop Multiply"

RedBull
06-13-2007, 12:33 AM
Weren't the PShop modes a feature introduced with 8.5?

Yes if not earlier... (7.5 or 8.1?)
Unfortunately with Nodes, they totally abandoned them again. (Sigh)

Captain Obvious
06-13-2007, 04:35 AM
Well, with the nodes, you have the Math multiply node. It should, logically, just multiply each of the RGB channel individually.

(So 25%,100%,50% * 100%,50%,25% = 25%,50%,12.5%)

Weepul
06-13-2007, 05:45 AM
This site (http://www.altyna.com/lw/specrefl.htm) sheds a little light:


UPDATE 04/26/03: As most LightWavers know, most of the mathematical layer blending modes, including Multiply which is used here, do not actually work the way they should. Multiply, for example, yielded rather washed out results in this hack versus actual radiosity. Fortunately, the inaccuracy turns out to be a gamma applied in the multiply operation. It has no business being there any more than the "slide" belongs in the Texture Channel... but it's there, and we have to work around it by adding a counter-gamma in Image Editor of 0.52 (noted in Step 4).
ALSO: set the gamma for your three channels to 0.52. This corrects the error encoded into the Multiply operation. (Thanks to Joth at Wet Cement for showing me the Image Viewer blending modes for doing comparisons of images right inside LightWave.)



Unfortunately with Nodes, they totally abandoned them again. (Sigh)
Not quite true. The Multiply mode in Nodes (not including the layer nodes) is the same as a Photoshop multiply, as are Additive (equivalent to Linear Dodge), Screen, Darken, Lighten, Difference, Color Dodge, and Color Burn. Missing as compared to the classic texture editor are Overlay, Soft Light, Hard Light, and Exclusion.