Mixed light in a single frame, say a warm tungsten lamp next to a cool daylight window, creates color casts that no single white balance setting can resolve. Raw Smart Objects in Photoshop let you process one exposure at two different white balance values and blend them precisely, without ever destructively baking in a conversion.
Setting Up the Raw Smart Object Workflow
Open your Raw file in Photoshop via Camera Raw, but instead of clicking Open Image, hold Shift so the button reads “Open Object.” This places the Raw file as a Smart Object layer. In the Layers panel, duplicate that layer by pressing Ctrl+J (Cmd+J on Mac). You now have two stacked Smart Objects, both pointing to the same Raw data. Double-click the bottom layer thumbnail to reopen Camera Raw, set the white balance to match your tungsten light source, around 2900K to 3200K, and click OK. Double-click the top layer, switch white balance to match daylight, typically 5500K to 6500K, and click OK. Each layer now carries a different color interpretation of the identical pixel data, which is the core advantage of this technique over white balance adjustments on flattened files.
Masking to Isolate Each Light Source
With your daylight-corrected layer on top, add a black layer mask by Alt-clicking (Option-click on Mac) the Add Layer Mask button. This hides the top layer entirely, revealing the tungsten-corrected version below. Paint white onto the mask with a soft brush at 60 to 80 percent opacity wherever the daylight is falling, such as near a window or open doorway. The transition between light sources is rarely a hard edge, so use a low-flow brush and build up gradually. For a portrait with window light on one side and a practical lamp on the other, you may find you only need to mask a vertical strip running down the center third of the frame. For scenes where the mix is more diffuse, like an interior where ceiling lights and skylights overlap, the masking work is more labor intensive but the principle is identical.
Pay close attention to skin tones in portrait work. Use the Color Sampler tool to check that neutral grays on shirts or walls read close to equal RGB values before calling a blend finished. If the transition shows a visible seam, reduce the mask edge hardness further by applying a 3 to 5 pixel Gaussian Blur directly to the mask layer via Filter > Blur > Gaussian Blur.
Adjusting Exposure and Tone Independently Per Light Zone
Because each layer is still a live Smart Object, you can return to Camera Raw at any time and adjust not just white balance but also exposure, shadows, highlights, and tone curve for each zone independently. A window lit area is often brighter than a lamp-lit interior, so you may need to bring highlights down 0.5 to 1 stop on the daylight layer to keep the blend looking natural. The lamp-lit zone may need a shadows lift of plus 20 to 30 in Camera Raw to open up the darker corners without affecting the exterior exposure. This multi-pass approach is far cleaner than trying to resolve color cast with targeted hue corrections after flattening, because you are working with the full tonal latitude of the Raw file at each step.
For event work, where you may have fluorescent overhead lights mixing with flash, open the tungsten-corrected layer in Camera Raw and drag the Tint slider green to negative 8 to minus 15 to cancel the green cast from fluorescents, since tint and color temperature together define the full white balance correction needed.
Common mistakes to avoid
- Converting the Smart Object to a regular layer before finishing. Once flattened, you lose the ability to reopen Camera Raw and you are stuck with a rasterized result. Always keep Smart Objects live until you are certain the blend is final.
- Setting both layers to the same white balance. The whole technique depends on each layer carrying a different color temperature. Double-check that your duplicated layer was actually edited independently by looking at the thumbnail previews in the Layers panel.
- Using a hard-edged brush for the blend mask. Mixed light transitions are gradual in real scenes. A hard mask edge looks artificial and draws attention to the correction.
- Ignoring the histogram while masking. Watch the histogram as you paint. If your blend causes highlight clipping in the masked region, the layer below is leaking through incorrectly.
- Applying additional white balance adjustments via an adjustment layer on top. Extra corrections compound on an already blended composite and make it nearly impossible to diagnose color problems later. Keep all white balance work inside Camera Raw.
FAQ
Does this technique work with JPEG files? No. Smart Objects opened from JPEG files do not reopen in Camera Raw with full Raw latitude. You need an original Raw file in a format Camera Raw supports, such as CR3, ARW, NEF, or DNG. If you only have a JPEG, your best alternative is to use selective color or targeted color grading adjustments instead.
Can I use this method in Lightroom instead? Lightroom does not support layer-based blending or Smart Objects natively, so this specific workflow requires Photoshop. However, you can set up multiple virtual copies in Lightroom with different white balance settings, export them, and blend the resulting TIFFs manually in Photoshop if you prefer to start in Lightroom.
How do I know which areas of the image belong to which light source? Shoot a gray card or a blank white wall under each light source separately if possible, and note the resulting Kelvin values shown in Camera Raw. In the scene itself, look for colored shadows: a tungsten-lit area casts orange shadows, a daylight area casts blue shadows. Areas where both light sources contribute equally are the hardest to correct and benefit most from a very soft, gradually built-up mask.