What's new

How to use opacity settings to create a composite imgage?


ktrichards

New Member
Messages
2
Likes
0
Hi! I'm new! I'm creating a composite image of 7 faces. They are each on a different 'Normal' layer. I want them to all be represented equally but the top layers are more prominent than the bottom. How much do I have to adjust the opacity levels to change this?

I know I can use 'multiply' to achieve this effect but I have to do it using 'normal'.

Any Advice?

Thanks :)
 

ALB68

Dear Departed Guru and PSG Staff Member
Messages
3,020
Likes
1,332
Hi ktrichards
Welcome to the forum. Hopefully you will find it informative and fun. I would say it would probably be difficult to give you a definite answer to your question without some images or a file to work with. However, our membership has some really experienced users and may have an answer for you. As a new member you can post images but not links until you have 5 posts.
 

Tom Mann

Guru
Messages
7,223
Likes
4,343
The standard formula to do this is to make the opacity of each layer equal to one divided by the number of the layer. In other words, the bottom layer has an opacity of one, the next layer up (ie, layer #2) has opacity 1/2, layer 3 is 1/3rd, layer 4 is 1/4, etc. When you are done, the contribution of each layer to the final result will be exactly equal. This can be proven mathematically.

The problem is that if you do it this way, none of the faces will ever be truly opaque -- they will always look ghostly, and you'll always be seeing background through them. The more layers you have, the more transparent each face will become. A composite like this is never done this way.

Instead, I strongly suspect that you haven't considered other options. For example, I just shot a night time shot of two huge trucks for an advertising poster. It would have been impossible to light them all uniformly, especially, without glints from the highly polished surfaces. Believe it or not, this is analogous to your "faces" project. The way I solved the problem for the truck shoot was to take around 30 exposures, each with a small light in a different position. I then put each exposure on a separate layer, and put each layer into "lighten" blending mode. Doing it using the "lighten" blending mode, the background stayed black, but only the brightest area in each exposure contributed to the final image. The result was stunning. I'll post some pix later today.

I suggest you strongly consider either cutting out each face, or using the "lighten" blending mode if they were photographed against a dark background. There are many other choices available for other situations.

If you post some example images, we will be able to help you better.

Cheers,

Tom M
 
Last edited:

ktrichards

New Member
Messages
2
Likes
0
The standard formula to do this is to make the opacity of each layer equal to one divided by the number of the layer. In other words, the bottom layer has an opacity of one, the next layer up (ie, layer #2) has opacity 1/2, layer 3 is 1/3rd, layer 4 is 1/4, etc. When you are done, the contribution of each layer to the final result will be exactly equal. This can be proven mathematically.

The problem is that if you do it this way, none of the faces will ever be truly opaque -- they will always look ghostly, and you'll always be seeing background through them. The more layers you have, the more transparent each face will become. A composite like this is never done this way.

Instead, I strongly suspect that you haven't considered other options. For example, I just shot a night time shot of two huge trucks for an advertising poster. It would have been impossible to light them all uniformly, especially, without glints from the highly polished surfaces. Believe it or not, this is analogous to your "faces" project. The way I solved the problem for the truck shoot was to take around 30 exposures, each with a small light in a different position. I then put each exposure on a separate layer, and put each layer into "lighten" blending mode. Doing it using the "lighten" blending mode, the background stayed black, but only the brightest area in each exposure contributed to the final image. The result was stunning. I'll post some pix later today.

I suggest you strongly consider either cutting out each face, or using the "lighten" blending mode if they were photographed against a dark background. There are many other choices available for other situations.

If you post some example images, we will be able to help you better.

Cheers,

Tom M
Thanks so much for your post, the formula you posted worked perfectly! I would be interested to see your truck advertising poster pix!

ktrichards
 

Tom Mann

Guru
Messages
7,223
Likes
4,343
Here's a quick animation (just for educational purposes) that I put together to show you how I composited over a dozen individual shots into a single, evenly illuminated shot. The trick was to use the "lighten" (or similar) blending mode. In your case, the individual shots would not be parts of a larger whole, as they were in this case, but completely separate images, hopefully with black or some dark region around each of the subject(s). I'll go into it in more detail later.

Also, I should mention that a side benefit of this technique is that I didn't have to do anything special to remove my assistant from the final product. Because she was always in silhouette, the area of the truck that she blocked in any particular shot was always filled in by the other shots.

Regards,

Tom

PS - The final frame in this animation is just the result of this 1st step of the process. This was followed by glint removal, further evening out of the light, the inclusion of about twice as many component images, including more at each end, wrapping around the fronts of both trucks, other shots with the lights aimed upwards, the inclusion of a few shots with the lights on the trucks turned on, plus quite a few final tweaks. Obviously, the camera was mounted on a really substantial tripod during all of these exposures to prevent any camera movement, whatsoever.
 

Attachments

Last edited:

Top