Combining images yet retaining each level of "brightness"...

[Clutch Cargo]

I would like to combine two images into one yet retain each image's original brightness (for lack of the proper term), when the are combined. For now the only way I see of combining layers is decreasing the opacity of one so the other shows through. But now I have reduced one images visual appearance of say 50% (opacity).

If I merge the two images the one on top just covers the image layer below it. Am I not using a proper tool? What should I read up on regarding this/ Hope I am making sense here.

Thx,

Clutch

 

[ibclare]

Hi Clutch, welcome to the forum. I am not sure I follow you exactly.

Would you post, first, the two images you are combining, then a sample of the result? Upload the psd if you like so we can get a better understanding of what you're doing and why it is working or not working. Thanks a bunch.

 

[Clutch Cargo]

Hey, thanks for the quick reply. Let me show you with a very basic example and I do mean basic.

So I have a layer called horizontal, and a 2nd layer called vertical. They are nice an bright colors on their own. But if I want these to on the same image I lose there original brightness. I have to reduce the opacity and I get the following results. Now, I suppose there is a way, some sort of cutting/pasting the two colors on one layer and literally moving them onto the other layer. But the images I will be "mixing" are a lot more intricate and will have many more layers.

So I am looking at ideas/suggestions on how to preserve the "originality" as best as possible when combining.

 

[Tom Mann]

The problem you describe is well known. In the real world, intensities of light are, with few exceptions (eg, lasers), completely additive. So, if you have a red circular source of light at a given intensity shining on a piece of white paper, and a green source of light at the same intensity doing the same, what you will see is a yellow area with double the individual intensities. The same is true of non-primary colors, as well.

The problem you observed arises when one tries to represent light intensities by numbers that only run over a limited range of values, eg, 0-255.

If you "add" (using the "color dodge" layer blend mode) pure bright red (255,0,0) to pure bright green (0, 255, 0), everything works out fine and you'll get a pure bright yellow (255, 255, 0).



However, if you try to add non-primary colors like (255, 100, 100) to (100, 255, 100), the limitations of the numerical representation prevent you from getting (355, 355, 200), which is what you would get in the real world. Instead, the best it can do is (255, 255, 100), and that's a very different color from what you expect.

This applies to the example you posted. Your red and green brush strokes are nearly pure primaries. In other words, they are nearly zero in two of the channels. OTOH, your yellow stroke is close to (255,255,0), and your orangish stroke is around (255, 242, 57), so even if you use the correct layer blend mode (ie, "linear dodge (add)") instead of the "normal" mode (at 50% opacity) that you used, you still won't get the correct colors at all the intersections.

About the best one can do is reduce the overall intensity of each of your two layers to half of its original value so that none of the channels exceed 127. Then, when they are added together (ie, in linear dodge mode), all the colors (including the intersections) come out correctly because no channel can possibly exceed 255. The result is shown below. It's very similar to what you got using "normal" mode with the top layer at half-opacity.



Unfortunately, it's dim, and there's no way around this if you need the hues and saturation values to be correct.

Of course, for many applications, this is unacceptable, so people "cheat" and use a different layer blending mode (eg, "screen") with the full intensity starting brush strokes, and get something that is brighter, but the hues and saturation values at the intersections are off from what would happen in the real world. This result is shown immediately below.



HTH,

Tom

 

[dv8_fx]

What needs to be done may depend on the images you are combining in term of color and detail.

Perhaps you can upload at least a small cropped section of the psd file with the layered images in question so we can experiment a mix you're looking for.

 

[Clutch Cargo]

I can't upload a portion of the work as it would be too large to upload. But here is what we are doing. We are taking daytime aerial imagery and creating nighttime imagery from it. A large multi-year project as we will be doing this for the entire United States. The nighttime example is the result of some 13 layers and several of those need to have their brightness adjusted for the right balance between highways/freeways and residential streets.

So I was looking at perhaps some tools or methods I was not aware of that might help. Right now, when I blend layers I have to go back and increase the brightness to make up for the loss when using opacity sliders. This is where the "art" comes into play but whatever the method it will have to be automated for 100,000's of images (whew!). So anything to set up the template easier is what I seek. Right now I need to check up on how to create layers I can edit without having to always make a copy of it to save the original. Forget what that is called...

Tom, how did you create that last image as both have the same intensity as the original? I am not so concerned where the colors overlap. It's the other areas I would like to preserve like your example.

 

[Tom Mann]

OP: "...Tom, how did you create that last image as both have the same intensity as the original? I am not so concerned where the colors overlap. It's the other areas I would like to preserve like your example...."

I used the "screen" layer blend mode.

(TJM: "...Of course, for many applications, this is unacceptable, so people "cheat" and use a different layer blending mode (eg, "screen") with the full intensity starting brush strokes, and get something that is brighter, but the hues and saturation values at the intersections are off from what would happen in the real world. This result is shown immediately below....")


HTH,

Tom

 

[ibclare]

Is there an inversion of the original image applied here? A sepai toning to turn the highlights brown? Curves adjustment?

Is this the exact kind of thing you want to mimic Clutch, with all the details completely blacked out?

 

[Clutch Cargo]

Yes, there is lot's of color adjustments, curves, saturation, masking, etc. Testing many different methods for the results we are looking for. Regarding the details being blacked out, no in fact we plan to adjust that layer (the base) to create additional type lights and forms of the buildings and the like. This example shows one of my concerns, with so many layers and opacity settings the background eventually gets washed away sort of speak.

 

[dv8_fx]

So what you want is to overlay the color lines and whatever planned in future on the satellite image without affecting the original? But at a night view?

 

[ibclare]

I came up with this. I think it would need adjustments beyond my skill. But do you think it might be a start?

I inverted the original to bring up the darks and make the roads whiter. I sued a cureves adjustment to darken the blacks and brighten the highlites. Then I added a photo filter with sepia at 100%. I duplicated this. (though it didn't add a lot) SO this is what I came up with:



This would easily become an action. Any selections beyond that would probably be manual - I would think.

 

[ibclare]

This one adds a couple brownish layers,set to multiply and opacity decreased.



I think dv8's example is a good one; I didn't see it before I experiemented. Let us know what you think.

 

[Clutch Cargo]

Interesting ibclare, the issue revolves more around if you took the image you worked on above as several layers how would you maintain each levels' intensity (what I have been calling brightness), after making adjustments then combining the layers? That's my issue.

Let me ask a question here, is there a tool or process to edit a layer and then if I don't like it it reverts back to its original state? Right now, I am having to duplicate the layers, try all my edits, then if I don't like it I have to EDIT/STEP BACKWARD which many steps and is very laborious. I am sure there is an easier way? Or a term for this I am unaware of?

 

[MrToM]

I am sure there is an easier way? Or a term for this I am unaware of?

There is!

Use 'Snapshot' in the 'history' palette.

Create a 'snapshot' before you start your edit, edit away, click the saved 'snapshot' in the history palette and you'll be right back to where you started.

I think the other members have pretty much covered your original question so I'll just add the above.

Regards.
MrTom.

 

[Clutch Cargo]

Thx for all your help on this matter...

 

[dv8_fx]

To add to what MrTom mentioned.... you can use the History brush or Eraser set to Erase to History....

Using the History brush tool setting, select the snapshot state taken earlier or state in the history and brush on the areas you want to restore. The History brush will restore attributes from an earlier point in an images history...




You can also use the Eraser tool set to Erase to History.




You can use these tools and settings provided you did not delete the layer you want to restore or saved the work at some point and want to restore a point in the history state prior to saving it.