Today’s Question: I remember a long time ago seeing you demonstrate a technique where you could combine two images based on brightness values, so that you could reveal only the brightest areas of one image in another. In your example you were combining bright clouds into another image. Can you remind me how that is done?
Tim’s Quick Answer: The technique you’re referring to involves the use of the “Blend If” sliders in Photoshop to blend two layers based on brightness values for each layer.
More Detail: While the “Blend If” sliders technique only works well under relatively specific conditions for combining two images into a composite, when it does work it can seem quite magical. The key is to use the “Blend If” sliders when there is a very clear separate in tonal values among the areas of an image you want to hide versus reveal in the composite image. Note that at the end of this answer I’ll reference a video tutorial that is available on this subject.
For example, let’s assume you want to create a composite image where a subject photographed against a bright sky is combined with a better sky in another image. You would first open these images as layers in Photoshop. From Adobe Bridge you can select the two images and then from the menu choose Tools > Photoshop > Load Files into Photoshop Layers. From Lightroom Classic you can select the images and from the menu choose Photo > Edit In > Open as Layers in Photoshop.
As you’d like, you can rearrange the order of the layers by dragging the thumbnails into a different order on the Layers panel. In this case we’ll assume the image of a subject against a bright sky is the upper layer and the replacement sky is the lower layer.
At this point you can select the upper image layer and then click the “Add new Layer Style” button (the “fx” icon) at the bottom of the layers panel and choose “Blending Options” from the popup menu.
In the Blending Options tab of the Layer Style dialog go to the Blend If section and make sure the popup next to the “Blend If” label is set to Gray so you’re blending images based on brightness values. Since at this point we want to hide portions of the current layer, we’ll drag the black slider if we want to hide dark areas and the white slider if we want to hide bright areas. In this example we want to hide the bright sky in this layer to reveal the better sky below, so we would drag the white slider toward the left.
After finding the optimal position for the slider in terms of hiding and revealing pixels to create a good composite image, some feathering or blending will be needed to improve the quality of the result. To enable this feature, hold the Alt key on Windows or the Option key on Macintosh while dragging one side of the white slider outward. This will split the slider into two smaller handles, and the gap between those handles represents feathering for the composite image. Adjust the position of both halves of the slider to optimize the composite and blending of the images.
If you want to reveal additional areas from the image below you can use the “Underlying Layer” sliders. For example, if there are bright clouds in the image of the sky for the lower layer, you might want to have some of those clouds appear over the relatively dark subject, to make it appear the subject is partially hidden among the clouds. To reveal pixels from the underlying image you drag the black slider to reveal dark areas or the white slider to reveal bright areas. So, in this example you would drag the white slider for Underlying Layer to reveal some of the bright clouds below, splitting the slider into two halves as outlined above so you get a blended result.
If you’re a GreyLearning Ultimate Bundle subscriber, you can watch the recording of my presentation on “Creating Composite Images” in my Photoshop Ultimate Live Learning series. After signing in to the GreyLearning website (https://www.greylearning.com/users/sign_in) you can follow this link to view the recording (the Blend If topic starts at about 34:22 in the recording):
If you’re not already a GreyLearning Ultimate Bundle subscriber, you can sign up for just $99 per year by using the link below to get started. You’ll then have full access to all content in the GreyLearning library, including all recordings from the Ultimate Live Learning series. Here’s the link:
https://www.greylearning.com/bundles/greylearning-bundle?coupon=golive
