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I have a New York skyline image that I want to use as a background texture image.

enter image description here

Here is the .blend:

I currently can not control the emission value for the individual "lights" in the picture, so is there a way that I can? Using an image for the emission factor would be optimal.

In rendered view with emission node setup for image:

enter image description here

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    $\begingroup$ What do you mean "individual" lights. Do you want to control separately light from sky and buildings or specific window? $\endgroup$ – vklidu Feb 15 at 13:43
  • $\begingroup$ That's what I want to do. $\endgroup$ – Nate_Sycro27 Feb 15 at 14:31
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    $\begingroup$ You would have to be more specific what do you expect from final result - what do you want to achive with that (some mockup image would be helpful). $\endgroup$ – vklidu Feb 15 at 16:01
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Here's one possible way to do what you want, if I understand your request properly.

enter image description here

The mix shader on the lower left is just the one that comes from the Images as Planes addon. That could just as easily be the direct Color out of the Image node. What I'm doing here is crushing the darker areas so that the image is mostly just the lights and the skyline. This goes into an Emission shader which, by use of the Is Camera Ray output as the Mix Shader factor, lights the scene but doesn't change the appearance of the image.

enter image description here

If this isn't what you're looking for, please update your question to give more information.

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There is many possibilities to do separation, but also with so many limits, that make it almost nonsense.

  • First limit is 8bit depth of your JPEG, should be 32bit like Open EXR. 32bit gives you much wider color range (especially to separate sky).
  • Second limit is bouncing light that make it totaly impossible to separate all indirect light for re-lightning make looks "normal".

Light (color) can be separated by intensity in material like with Power node or by color that is better to work in Compositor with all the Matte nodes or manually by masking some areas. But as I wrote one light contaminates other so there is no simple way in this kind of image.

It always depends what do you want to achieve.

enter image description here

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  • $\begingroup$ I decided upon using a color ramp to control the emission factor, and a RGB to BW node to the colorRamp from the image. Thank you though! $\endgroup$ – Nate_Sycro27 Feb 15 at 16:06
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Object Material

Simple control of emission without affecting source appearence. Quite surprised how light wrapped Sphere just from front direction. But object is not lighted from front (black faces in center), because there is not any light behinde camera.

enter image description here


World Matrial

You can also use the image as World material mapped for Camera window (Texture coordinates > Window).

enter image description here

Illusion of environmental light you can quite quickly fake by extending original image by mirroring and a bit of repainting to eliminate sun light from backside (to create like 360 panorama image). Since its just for envi light you don't have to care to much.

Camera Properties > Lens > Focal Lenght 17 brings envi texture into original image horizontal range view. Compensate vertical distortion you can in Texture Coordinates node Scale Z like 6, but lightning looked better without, so I left it.

enter image description here

Note: pay attention to node type - for Camera Window its Image texture for envi light Equirectangular texture

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