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# need help: linear lighting as an imaging effect

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If you run Photoshop, open two images and combine them by pasting one onto the other as a new layer and set the blending options of the added layer to Linear Light, you''ll get a certain kind of effect that I''m after. However, there isn''t much info on the web about this kind of blending. I presume it''s a form of convolution (see the below examples, note the zeroes at the edges of the destination image), but I really can''t tell what is convolved with what (or, I could very well be mistaken altogether). Here''s a 5x5 pixel outtake from two images (a square-shaped region in the upper left corner) and the resultant image when S2 is blended on top of S1 (incidentally, blending order doesn''t play much of a role here). I''m only posting the red channel here (as I presume blending is done per channel): S1:
28	28	28	28	28
30	30	30	30	30
32	32	32	32	32
32	32	32	32	32
30	30	30	30	30

S2:
74	103	110	85	75
101	104	159	214	172
132	128	123	214	172
133	130	128	127	126
135	131	125	121	125

D:
0	0	0	0	0
0	0	92	202	118
40	32	22	20	22
42	36	32	30	28
44	36	24	16	24

Can anyone link me to a website that explains the blending equation or perhaps explain the correlation between the three? Cheers, Crispy

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http://www.pegtop.net/delphi/blendmodes/#stamp

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quote:

From Photoshop 7.1 help

Linear Light

Burns or dodges the colors by decreasing or increasing the brightness, depending on the blend color. If the blend color (light source) is lighter than 50% gray, the image is lightened by increasing the brightness. If the blend color is darker than 50% gray, the image is darkened by decreasing the brightness.

It's a linear filter as it seems...

[edited by - Nik02 on October 7, 2003 10:44:17 AM]

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AP: that is one very useful clickerson! Thanks a million!

Nik: since it is expressed as (a + 2*b - 1), eg it contains a multiplication, it isn''t linear, but it''s definitely not a very difficult filter, that''s for sure.

PS - I was wrong - blending order is important, based on the equation.

Anyway - cheers to both of you.

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quote:
Original post by Crispy
since it is expressed as (a + 2*b - 1), eg it contains a multiplication, it isn''t linear

You''re right, i got the terms mixed up. I saw it in my mind as linear because it''s so simple

-Nik

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