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Sky on demand

The sky is often the backdrop for our landscape photographs. But sometimes its appearance leaves us disappointed. Since version 22, Photoshop has made it easier for us to replace it.

The sky is almost non-existent in the seaside image (Olympus OM-D EM1 MkII). The people and the parasol cut off the horizon. The photo of the sky was taken a few months earlier, at the end of the day (Nikon D850).

Automated Sky Replacement

Landscape is a matter of encounter between earth and sky. But how often are we enchanted by the light that shapes the earth’s landscape, only to regret that the sky isn’t in harmony? The software Luminar has made a name for itself as an expert in this field. Photoshop introduced a similar feature in version 22, in 2020. In both cases, a library of skies is offered, but you can also upload your own images.

By clicking on Edit > Replace sky… a window opens with a predefined sky. Its definition is displayed by hovering the mouse over it. Click on the drop-down menu to access a gallery organized by folder: Blue Skies, Spectacular, Sunsets.

Sky Selection Criteria

Whatever software is used, there are four key criteria for a credible result. The sky must blend in with the rest of the image without looking artificial. The resolution of the two images, earth and sky, must be close enough to avoid differences in sharpness. The noise level should be the same. Objects or people crossing the horizon can cause halos due to poor sky blending.

Check Files

The first three cases are a matter of common sense. Harmonization can be quickly checked by copying and pasting an image of the sky onto the photo you want to change. If the angles and focal lengths used for the two views are very different, the scale and perspective will be distorted. The resolution of the sky image is perfect if the same camera is used for the sky and the foreground, and the ISO sensitivity of the two is close enough to avoid a difference in noise. If one of the two images is cropped, a difference in the number of pixels between the two files of less than 30% will avoid a discontinuity in sharpness between the two parts of the composite.

Merge Tolerance

However, the sky is not a sharp object, so the resolution tolerance is pragmatic. Our first image was taken with an Olympus OM-D EM1 MkII at a focal length of 15 mm (equivalent to 30 mm full frame) and a width of 5184 pixels. The sky was taken with a Nikon D850 at a focal length of 24 mm (8256 pixels). Theoretically, it should have been cropped to 6604 pixels in length (and 4953 pixels in height to match the 4:3 ratio) to maintain the same angle of view. However, the bright area of the sun in the sky image would not be aligned with the reflection of the sun in the water. So the image is cropped so that the bright spot in the sky corresponding to the veiled sun is above the reflection of the sun in the sea, on the right-hand side of the image. This file could be resized to have the same resolution as the foreground (5184 x 3888 pixels), but the difference in size is automatically adjusted as the sky changes.

Custom Sky

You can import images from your computer’s hard drive into the Standard Skies Gallery (Get More Skies > Import Images…). Download Free Skies… takes you to the Adobe Creative Cloud.

Blend Sky

Shift Edge controls the depth of the sky overlay in the image. Fade Edge, a type of feathering, adjusts the transition between the two images. The default settings give a balanced result. Work on the image at 100% or 200% magnification to fine-tune the effects.

Sky Adjustment

The sky blend is further adjusted for brightness and colour temperature. This ensures that the colour of the sky matches the rest of the image, giving a realistic overall impression. The size of the sky is automatically adjusted to fit the image when the scale is set to 100. Flip reverses the orientation of the sky.

Foreground Adjustment

The lighting mode has two blending modes: Multiply and Screen. Multiply darkens the transition zone of the foreground in contact with the sky, while Screen lightens it. The color control adjusts the color temperature of the foreground.

Output to New Layers

There are two types of output: layer duplication and layer output. The latter shows the combination of several layers and blend masks. So you can work on each layer separately to achieve a pleasing blend with the sky.

Keeping Layers

The power of Photoshop lies in the automatic precision of the masks, which render the new sky in a natural way. And the collage can be exported as layers to adjust the fusion masks and the colour balance of the sky in relation to the ground.

Discover the photography courses at Spéos

Spéos offers various training courses ranging from simple one-week photography courses (initiation and advanced level) to 3-year courses. The long courses to become professional photographers allow you not only to master all the photographic techniques and its vocabulary (blurs, hyperfocus, sharpness zone, depth of field, backlighting, focal length, shutter release, autofocus, wide-angle, rule of thirds, etc.), but also all the stages of shooting and image processing.

Visiting the school allows you to discover the premises, the studios and the equipment, and is undoubtedly the best way to familiarize yourself with your future way of working. This is why, in addition to the open days, Spéos offers throughout the year personalized visits by appointment to come and discover the school with a member of the team.

Text and photos: Philippe Bachelier, teacher of Printing techniques at Spéos

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