Use creative editing techniques
Take your images further by correcting inconsistencies and adding artistic effects in editing software
The conditions we experience in the field when shooting low-light and astro images push our cameras to the extremes of their designed capabilities. The absence of significant levels of ambient light presents issues relating to digital data gathering and therefore the signal-to-noise ratio, calling on the advanced image processing algorithms found in the latest cameras to reduce chroma and luminance patterning. Furthermore, the extreme contrasts of exposure found in urban areas, as highoutput artificial light sources are mixed with deep shadows, test the dynamic range of the camera’s sensor. So while today’s DSLRs and advanced CSCs are precision tools, the photographer’s technique must be perfected, since there is a fine margin for error. Post-processing is therefore a useful buffer for correcting minor imperfections and assisting the camera in rendering sufficient detail and tone.
However, when working with files containing less information, conflicts of necessity become apparent, such as the need for greater exposure but at the risk of enhanced grain, or the requirement for noise reduction at the expense of fine detail. These aspects are more easily masked in daylight shots, so a considered process is essential. Many photographers begin their low-light processing workflow with adjustments to exposure, since the high contrasts often produce the impression of saturated colour – necessitating hue and saturation adjustments after work has been conducted on brightness. An increase in exposure can reduce apparent saturation and darkening an area of the frame can have the inverse effect. Visit the HSL (Hue Saturation Luminance) panel in Camera Raw or Lightroom to apply appropriate compensating adjustments, after making changes to global or local brightness.
The next area of focus is correction of image rendering defects, from both the lens and camera body. Lens distortion correction, vignetting removal and noise reduction will address the most prominent deficiencies of images shot in poor or highcontrast lighting. Finally cropping can aid composition, which can be compromised by unsightly fall-off in exposure. Areas of deep shadow can be overlooked in-camera, adding unwanted empty space to the frame, but these can later be removed using the Crop Tool.
1 USE LOCAL ADJUSTMENTS
When working with scenes containing areas of deep shadow and extreme brightness, it is unlikely that all areas of the frame will require identical processing. Therefore applying local adjustments using the Adjustment Brush in Camera Raw and Lightroom, or using layer masks in Photoshop, will give a more customisable editing style. Lift shadows, modify colours and enhance micro contrast.
2 BLEND WHITE BALANCES
As discussed, mixed light sources make it challenging to avoid unwanted colour casts. Blending files of varying white balance settings creates a finished image with the best of all colour ranges. WB can be bracketed in-camera, although the following process saves card space by using a single base RAW file.
2 . 1 CHOOSE A PRESET
Open your RAW file in a compatible editor and select a white balance preset from the drop-down menu. Choose one that enhances the cool tones in the image, such as those from blue neon lights or natural light reflections.
2 . 2 ADJUST GENERAL SETTINGS
Move the Exposure and colour control sliders to improve the overall tonality. While these settings can remain constant for all WB frames, experiment with minor differences to complement the cool or warm colours.
2 . 3 OPEN MULTIPLE COPIES
Rather than opening an image as usual, hold down Alt/Opt and click on Open Copy. This will allow you to re-enter your RAW editor, select another WB preset or Colour Temperature and open these varied files in Photoshop.
2 .4 MERGE LAYERS
With all of your duplicate files open, stack them as layers in a single document and use layer masks to reveal areas of each copy. This will allow both warm and cool tones to be maintained in a single image, for better colour depth.
“Use Define to target specific noise types”
3 CONSIDER MONOCHROME
While not a genre that immediately suggests itself for monochrome conversion, with the right scene a black and white image can better focus attention on light and shadow. Converting night street scenes gives a classic and timeless feel to well-known locations. Consider using a plugin such as Silver Efex Pro from the DXO Nik Collection.
4 CREATE 32-BIT FILES
As an alternative to tone-mapping for extended dynamic range, merge multiple exposures into a 32-bit TIFF file in Photoshop’s Merge to HDR Pro feature. Just select 32 Bit and use the default settings. Then open the file in Lightroom or ACR to adjust shadows and highlights. The file contains more information so there is more scope for retrieving detail.
5 REMOVE VIGNETTING
With strong light sources and minimal ambient light, exposure diminishes rapidly, moving away from the source. This often results in edge vignetting in low-light shots, exacerbating native optical darkening. Use the Lens Correction filter to subtly lighten the frame periphery, remaining mindful of noise. Alternatively, use the Adjustment Brush with Noise Reduction loaded for simultaneous brightening and smoothing.
6 LUMINOSITY SHARPENING
Long-exposure images may often need some sharpening, due to micro shifts in camera position across the exposure time. Sharpening on a new layer in Photoshop and changing the Blend Mode to Luminosity will restrict sharpening to detail, reducing accentuation of colour noise and minimising halo effects in high-frequency areas. This allows more aggressive sharpening should it be needed.
7 NOISE REDUCTION OPTIONS
NR is always going to play a major role in finalising a low-light image. While Lightroom features advanced reduction tools, an external application like Define, from the DxO Nik Collection, can provide precise targeting of specific noise types and effective smoothing of grain, with minimal damage to detail integrity.
7. 1 OPEN THE IMAGE
You can choose to either open your file directly in Define, or from within Lightroom or Photoshop as a plug-in. In Photoshop all of the DxO Nik filters can be found in the Filter menu.
7. 2 REDUCE LUMINANCE NOISE
Minimise the grain content of the image using the Contrast Noise slider. This will add a blur to the image, reducing the texture. Use this with care to reduce sharpness loss.
7. 3 WORK WITH COLOUR NOISE
Select Colour Ranges as the Method in the Reduce tab. Then select colours in the image that require more work. This provides a more sophisticated style of NR to maintain quality.
7. 4 USE MASKING
Click the Brush button to open in Photoshop with a Layer Mask. This allows you to apply localised NR, to remove patterns from the most negatively affected areas while limiting destructive impact detail.