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How to merge bracketed exposures into an HDR photo

Advanced8 minutesUpdated

Quick answer

In Lil Cactus, choose File then HDR Merge…, click Add photographs… and pick your brackets, for example shots at −2, 0 and +2 EV. Lil Cactus reads each photo’s exposure from its camera data; keep Align photographs on, set Deghosting to Off for a perfectly still scene such as the sample, tick the box confirming a static scene, and click Merge HDR. Then choose Image then Tone Map to SDR…, leave White point at its starting value, the brightest value in the photo, adjust Exposure (0.5 EV for the sample) and click Create SDR copy to get a normal 16-bit photo.

A road through a red-rock canyon at sunset: in the single normal exposure the sky around the sun burns out to white and the canyon walls are dark; in the merged and tone-mapped HDR the clouds around the sun and the glow show, and the walls are lighter
Drag the handle to compare the original with the result made in this tutorial.
Time
8 minutes
Level
Advanced
You need
2 to 32 photos of the same scene at different exposures, ideally from a tripod
Works with
JPEG, PNG or TIFF brackets, 8 or 16 bits, sRGB
Open Lil Cactus

Sample files:−2 EV0 EV+2 EV

Free, no sign-up. Your photos stay on your computer.

A camera captures a limited range of brightness in one shot. Point it at a sunset and either the sky burns out or the ground goes dark. Bracketing means taking the same scene several times at different exposures: one dark enough to keep the bright sky, one normal, one bright enough to open the shadows.

HDR merge combines them into a single image that holds the whole range, stored as 32-bit floating-point values with far more brightness range than any screen can show. Tone mapping then squeezes that range back into a normal photo, compressing the highlights gently instead of cutting them off.

Merge HDR in six steps

  1. Shoot or collect your brackets

    Use a tripod if you can, and keep the aperture, ISO, zoom, white balance and focus fixed; change only the shutter speed. Two stops (EV) apart is typical: −2, 0, +2. Many cameras do this automatically with auto exposure bracketing (AEB). Save JPEG, PNG or TIFF files. HDR Merge doesn’t read RAW files directly: open each RAW in Lil Cactus with identical Camera RAW settings and export it with File then Export then TIFF…, which keeps 16 bits and the camera data, including the shutter speed.

    To follow along, download the three sample brackets from the top of this page. They are rendered from a constructed scene whose sky and sun are far brighter than a single photo can hold, and tagged with shutter speeds 1/500, 1/125 and 1/30 s, so they behave like brackets from a tripod: the −2 EV frame keeps the clouds around the sun that the others burn out, and the +2 EV frame opens the shadows, with less noise there than the darker frames.

    Three exposures of the same canyon road at sunset side by side: dark at −2 EV with clouds and the sun’s glow in the sky, normal at 0 EV with a burnt-out sky around the sun, and bright at +2 EV with light canyon walls and a white sky
    The sample brackets: −2, 0 and +2 EV.

  2. Choose File › HDR Merge…

    You don’t need to open a document first: HDR Merge… is in the File menu, just below Open…, and creates a new document.

    The File menu with HDR Merge highlighted, below New and Open
    File then HDR Merge…

  3. Add the photographs

    Click Add photographs… and select all the brackets at once. Each appears in a row with its size and color profile. Relative EV is filled in from the shutter speed in the camera data, labeled Shutter metadata: −2, 0 and 2.058894 for the sample (about 2.06), because 1/30 s, like the shutter speeds cameras record, is a little more than two stops from 1/125 s. If a photo has no camera data, type its EV yourself; positive means brighter.

    Reference marks the photo everything is aligned to; by default the middle exposure. If something moved, such as a person or a branch, choose the photo where it looks best.

    The HDR Merge bracket list: three rows for the −2, 0 and +2 EV photos, each with its name, size, Embedded sRGB and its Relative EV, with Add photographs… ringed
    The three brackets, with EV read from their shutter speeds. Add photographs… is ringed.
    1. Relative EV, from the camera data

  4. Check the options and click Merge HDR

    • Align photographs (on by default) corrects small camera movement between shots, so handheld brackets work too. Leave it on.
    • Deghosting (default Medium) uses the reference photo wherever something moved, so you don’t get see-through people or doubled leaves. Off is for a perfectly still scene: set it to Off for the sample, because with Low, Medium or High the merge refuses it as not having enough clear overlapping detail. High looks for finer movement. Changing it clears the confirmation box below.
    • Tick the confirmation box (its wording follows the Deghosting choice): it tells Lil Cactus the scene is static and the photos share settings, which the merge relies on.

    Click Merge HDR. The status line at the bottom of the dialog names each stage and shows its percentage; the three 1.6-megapixel sample brackets take about a minute. When it finishes, a message reads 32-bit float · SDR preview. It may add that some clipped channels could not be recovered; File then File Info lists the merge’s notes.

  5. Choose Image › Tone Map to SDR…

    The merged document is 32-bit floating point; the status bar reads 32-bit float · SDR preview. What you see is only a preview: to edit and export it as a normal photo, choose Image then Tone Map to SDR…

    • Exposure (−5 to 5 EV, default 0) sets the overall brightness.
    • White point (EV) sets how bright a scene value must be to become pure white. It starts at the brightest value in the photo (2.07 for the sample), so the brightest areas just reach white; a strongly colored highlight, such as the red glow around the sample’s sun, can still reach full strength in one channel. Raising it compresses the highlights more; lowering it lets bright areas burn out for punchier contrast.

    The sample keeps the starting White point and raises Exposure to 0.5. Click 100% above the preview to judge detail, then Create SDR copy.

    The Image menu open below the menubar, with Tone Map to SDR highlighted at the top above Mode and Adjustments
    Image then Tone Map to SDR…, available for 32-bit documents.
    The Tone Map to SDR controls: Exposure 0.5 EV, ringed, and White point 2.07 EV
    Exposure raised to 0.5 (ringed), with White point left at its starting 2.07.

  6. Edit and export the SDR copy

    Create SDR copy opens a new 16-bit sRGB document, named HDR Merge – SDR, and straight away the Export as PNG dialog: export from there, or click Cancel to edit first. The HDR document stays open. Edit the copy like any photo, with Curves or Photographic Development for contrast and color, then export it with File then Export then JPEG…

    To keep the full HDR values for later, save the HDR document with File then Save As then Lil Cactus Project… (Ctrl+Shift+S or ⇧⌘S).

    An enlarged patch of sky to the right of the sun: bands of pure white between the clouds in the single 0 EV exposure, and cloud texture throughout in the merged HDR
    Sky to the right of the sun, enlarged: the single 0 EV exposure (left) and the HDR result (right).
    An enlarged patch of the shaded canyon wall: dark and murky in the single exposure, lighter with clearer rock texture in the HDR result
    The shaded canyon wall, enlarged: the single exposure (left) and the HDR result (right).

Only have one photo?

A single photo can’t become a true HDR image: what the sensor clipped is gone. But a RAW file often holds two or three stops more range than a JPEG. Lower Highlights and raise Shadows in Photographic Development, or use Shadows/Highlights on a JPEG, for a similar look within that photo’s limits.

Why merging recovers more than one exposure

Each bracket records a different slice of the scene well: the dark one the sky, the bright one the shadows. The merge estimates how each photo’s pixel values relate to real scene brightness (the camera’s response), aligns the shots, and for every pixel weights each photo by how well it recorded that pixel, trusting clipped values least. It doesn’t remove noise: where a darker frame contributes, its noise comes along. The result is one set of scene values, from the shaded canyon walls to the sun’s glow. Tone mapping first sets an overall brightness from the photo’s average (shifted by Exposure), then applies a smooth curve that rolls bright tones off gradually toward the white point instead of clipping them.

Fix common problems

Ghosts: see-through people or doubled leaves

Something moved between shots. Try a stronger Deghosting setting, tick the confirmation box again, and pick as Reference the photo where the moving part looks best. If the merge then refuses the photos, see the next entry.

“These photos do not contain enough clear overlapping detail to combine”

With Deghosting on, the merge needs detail that is clear in neighboring exposures. For a still scene, set Deghosting to Off; otherwise add exposures in between, for example every stop instead of every two.

Merge HDR stays grayed out

Tick the static-scene box (and Assign sRGB to all untagged inputs if it appears), and check the message under the options: every photo needs a Relative EV, and photos with camera data must share aperture, ISO and focal length.

“This photograph has a non-sRGB profile”

HDR Merge works in sRGB. Convert each bracket to sRGB first, for example with Edit then Convert to Profile… and Export, or export them as sRGB from your RAW developer.

Blurry or doubled edges everywhere

The camera moved too much for alignment. Shoot from a tripod, or use fewer, closer brackets.

What to do next

Coming from another editor

Photoshop
File › Automate › Merge to HDR Pro… In Lil Cactus the same job is File › HDR Merge… followed by Image › Tone Map to SDR…

HDR merging: questions and answers

How many exposures do I need for HDR?

Three exposures two stops apart (−2, 0, +2 EV) cover most scenes. Lil Cactus accepts 2 to 32 brackets; very high-contrast scenes such as a window interior may need five.

Can I merge RAW files to HDR in Lil Cactus?

Not directly. In Lil Cactus, open each RAW bracket with identical Camera RAW settings, export it with File › Export › TIFF…, then add the TIFFs to File › HDR Merge… The TIFFs keep the camera data, so the Relative EV is read from the shutter speeds.

Can I export a 32-bit HDR file from Lil Cactus?

No. On a 32-bit document, File › Export › JPEG…, PNG… and the other image formats open Image › Tone Map to SDR… instead, which makes a normal 16-bit copy to export. To keep the full HDR values, save the document with File › Save As › Lil Cactus Project…

Why does my merged HDR look gray?

A 32-bit HDR holds more range than a screen shows, and tone mapping compresses it. In Lil Cactus, lower White point in Image › Tone Map to SDR… for more contrast, then fine-tune the SDR copy with Curves.

Are my photos uploaded when I merge HDR in Lil Cactus?

No. Merging and tone mapping run in your browser on your own device, and the photos are never sent to a server. Optional statistics never include images; see the privacy policy.

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