Mathematical description of layer blend modes

J
Posted By
jeffc
Jan 18, 2005
Views
541
Replies
6
Status
Closed
OK, I have to admit. I don’t understand exactly what each layer blend mode in PhotoShop is doing. Simply looking at some sample pictures of blend modes with some cryptic explanation is not working for me :-). Even when a blend mode has mathematical name it doesn’t make sense. For example what "multiply" mode means? Does it mean if value of a pixel in a layer’s channel is 10 and in another layer is 5 then the resulting pixel’s value will be 50? OK, fine! Then what if these values are 100 and 100 respectively? Apparently the result should be clipped at 255? If we make this assumption then the resulting image will be all white with most of pixels clipped at 255. Whereas, the "multiply" mode makes the image darker suggesting there should be a scaling operation rather than a clipping operation.

Is there a book, or a link that explains complete mathematical operations of each blend mode on pixels? Thanks in advance.

How to Improve Photoshop Performance

Learn how to optimize Photoshop for maximum speed, troubleshoot common issues, and keep your projects organized so that you can work faster than ever before!

NE
no_email
Jan 18, 2005
On Mon, 17 Jan 2005 21:52:05 -0800, "Dr. J"
wrote:

OK, I have to admit. I don’t understand exactly what each layer blend mode in PhotoShop is doing. Simply looking at some sample pictures of blend modes with some cryptic explanation is not working for me :-). Even when a blend mode has mathematical name it doesn’t make sense. For example what "multiply" mode means? Does it mean if value of a pixel in a layer’s channel is 10 and in another layer is 5 then the resulting pixel’s value will be 50? OK, fine! Then what if these values are 100 and 100 respectively? Apparently the result should be clipped at 255? If we make this assumption then the resulting image will be all white with most of pixels clipped at 255. Whereas, the "multiply" mode makes the image darker suggesting there should be a scaling operation rather than a clipping operation.

Is there a book, or a link that explains complete mathematical operations of each blend mode on pixels? Thanks in advance.
This link may help
http://www.pegtop.net/delphi/blendmodes/
IB
Ina Bechhoefer
Jan 18, 2005
Fascinating explanations.
Thanks,
Ina

"ZONED!" wrote in message
On Mon, 17 Jan 2005 21:52:05 -0800, "Dr. J"
wrote:

OK, I have to admit. I don’t understand exactly what each layer blend
mode
in PhotoShop is doing. Simply looking at some sample pictures of blend
modes
with some cryptic explanation is not working for me :-). Even when a
blend
mode has mathematical name it doesn’t make sense. For example what "multiply" mode means? Does it mean if value of a pixel in a layer’s channel is 10 and in another layer is 5 then the resulting pixel’s value will be 50? OK, fine! Then what if these values are 100 and 100 respectively? Apparently the result should be clipped at 255? If we
make
this assumption then the resulting image will be all white with most of pixels clipped at 255. Whereas, the "multiply" mode makes the image
darker
suggesting there should be a scaling operation rather than a clipping operation.

Is there a book, or a link that explains complete mathematical operations
of
each blend mode on pixels? Thanks in advance.
This link may help
http://www.pegtop.net/delphi/blendmodes/
O
Odysseus
Jan 18, 2005
In article ,
"Dr. J" wrote:

OK, I have to admit. I don’t understand exactly what each layer blend mode in PhotoShop is doing. Simply looking at some sample pictures of blend modes with some cryptic explanation is not working for me :-). Even when a blend mode has mathematical name it doesn’t make sense. For example what "multiply" mode means? Does it mean if value of a pixel in a layer’s channel is 10 and in another layer is 5 then the resulting pixel’s value will be 50? OK, fine! Then what if these values are 100 and 100 respectively? Apparently the result should be clipped at 255? If we make this assumption then the resulting image will be all white with most of pixels clipped at 255. Whereas, the "multiply" mode makes the image darker suggesting there should be a scaling operation rather than a clipping operation.
I believe the levels from 0 to 255 are treated as fractions, so that they range from 0 to 1. (That’s also the way PostScript describes colours and greys.) So multiplying pixels with levels of 10 & 5, the calculation would go 10/256 * 5/256 = 50/65536 ~= 0.2/256, close enough to zero, while if both have values of 100 they’ll multiply to 10000/65536 ~= 39/256 or, in approximate percentages, 40% * 40% = 16%.


Odysseus
J
jeffc
Jan 19, 2005
"ZONED!" wrote in message
On Mon, 17 Jan 2005 21:52:05 -0800, "Dr. J"
wrote:

< some lines of original question snipped>

Is there a book, or a link that explains complete mathematical operations of
each blend mode on pixels? Thanks in advance.
This link may help
http://www.pegtop.net/delphi/blendmodes/

Thank you for this link. This is so far the most comprehensive explanation I have seen.
NE
no_email
Jan 19, 2005
On Tue, 18 Jan 2005 22:21:20 -0800, "Dr. J"
wrote:

Thank you for this link. This is so far the most comprehensive explanation I have seen.
No problem… was an easy search.
J
JeanK524
Jan 19, 2005
Outstanding reference. I apply blending to two channels of the same image instead of two different images. The site’s explanation should still apply. But it would be nice to find a tutorial on how to blend two channels.

"ZONED!" wrote:
On Mon, 17 Jan 2005 21:52:05 -0800, "Dr. J"
wrote:

OK, I have to admit. I don’t understand exactly what each layer blend mode in PhotoShop is doing. Simply looking at some sample pictures of blend modes with some cryptic explanation is not working for me :-). Even when a blend mode has mathematical name it doesn’t make sense. For example what "multiply" mode means? Does it mean if value of a pixel in a layer’s channel is 10 and in another layer is 5 then the resulting pixel’s value will be 50? OK, fine! Then what if these values are 100 and 100 respectively? Apparently the result should be clipped at 255? If we make this assumption then the resulting image will be all white with most of pixels clipped at 255. Whereas, the "multiply" mode makes the image darker suggesting there should be a scaling operation rather than a clipping operation.

Is there a book, or a link that explains complete mathematical operations of each blend mode on pixels? Thanks in advance.
This link may help
http://www.pegtop.net/delphi/blendmodes/

How to Master Sharpening in Photoshop

Give your photos a professional finish with sharpening in Photoshop. Learn to enhance details, create contrast, and prepare your images for print, web, and social media.

Related Discussion Topics

Nice and short text about related topics in discussion sections