What is Computer Generated Hologram (CGH)?
A computer generated hologram (CGH) is a holographic pattern created by mathematical algorithms and computational methods rather than by recording light waves reflected from a physical object. In traditional (optical) holography, a laser beam is split, and the interference between object and reference beams is recorded on a photosensitive plate. In CGH, the interference pattern is calculated digitally using Fourier transforms and other algorithms, then written onto a medium using a laser writer, electron beam, or displayed on a spatial light modulator (SLM). CGH enables the creation of holograms of objects that do not physically exist, or of scenes that are impossible to record optically (e.g., virtual 3D models, encrypted data). CGH is used for high‑security DOVIDs, machine‑readable holograms, 3D displays, and anti‑counterfeit features because the design can include custom, complex patterns that are extremely difficult to reverse‑engineer. Holoseal works with CGH origination specialists to create custom security holograms with unique, algorithm‑generated diffractive structures for brand protection.
🔬 How Computer Generated Holograms Are Made
The process transforms a digital 3D model or 2D image into a diffractive pattern that can be embossed or displayed. Here is the typical workflow:
1. Scene Design
A 3D model (e.g., a logo, product, or geometric shape) is created in CAD or 3D software. Alternatively, a 2D image with depth information can be used.
2. Algorithmic Calculation (CGH Generation)
An algorithm (often based on fast Fourier transforms – FFT) computes the interference pattern that would be produced if the virtual object were illuminated by a coherent light source. This calculation produces a 2D map of phase and/or amplitude values – the holographic fringe pattern.
3. Encoding & Optimisation
The calculated fringe pattern is quantised and encoded into a format suitable for the output device. For embossed holograms, the pattern is converted into a greyscale bitmap that controls the depth of the surface relief. For display holograms (e.g., on spatial light modulators), the pattern is loaded into an SLM in real time.
4. Writing the Master
The encoded pattern is written onto a photoresist plate using a laser writer (dot matrix) or an electron‑beam lithography system (for highest resolution). The exposed plate is developed, creating a surface relief master – exactly like an optically recorded hologram master.
5. Embossing or Display
For mass‑produced security holograms, the master is electroformed to produce nickel shims, which then emboss the pattern into metalized film. For dynamic displays, the CGH pattern is streamed to an SLM, creating a real‑time holographic image.
📦 Types of Computer Generated Holograms
- Binary CGH (B‑CGH) – Each pixel is either on or off (0 or 1). Simplest to manufacture, lower diffraction efficiency.
- Multilevel / Grayscale CGH – Each pixel has multiple phase levels (e.g., 4, 8, 16). Higher diffraction efficiency and image quality.
- Phase‑only CGH – Only the phase is modulated; amplitude is constant. Most common for high‑quality holographic displays and security masters.
- Amplitude‑only CGH – Only the amplitude is modulated; phase is constant. Less efficient, rarely used.
- Diffractive Optical Element (DOE) – CGH – Designed for specific optical functions (beam splitting, shaping) rather than image reconstruction.
🛡️ Advantages of CGH for Security Holograms
- Unlimited design possibilities – CGH can create holograms of objects that don’t exist physically (e.g., impossible 3D geometries, encrypted data).
- Enhanced security – The digital file (the CGH algorithm) can be kept secret. Without it, the pattern cannot be reverse‑engineered.
- Machine‑readable features – CGH can embed digital data (e.g., serial numbers, encrypted codes) directly into the diffractive structure, readable by specialised scanners.
- Perfect replication – Once the CGH master is created, millions of identical copies can be embossed.
- Integration with DOVIDs – CGH can produce complex kinetic effects (rolling bars, image switching) without the need for dot matrix origination.
⚙️ CGH vs. Optical Holography
| Aspect | Optical Holography | Computer Generated Holography |
|---|---|---|
| Recording method — | Physical interference of laser beams— | Mathematical calculation (FFT, iterative algorithms) |
| Object requirement — | Requires a real physical object or a mask— | Can create holograms of virtual objects |
| Resolution limit — | ~500 nm (laser wavelength limit)— | ~10 nm (e‑beam writing) – higher resolution possible |
| Security / secrecy — | Lower – the master is a physical object— | Higher – the digital algorithm can be kept secret |
| Complexity of effects — | Limited by physical setup— | Unlimited – can generate any diffractive pattern |
| Cost for custom master — | Low to moderate— | Higher (computational time, specialised writing) |
🔐 Applications of CGH in Security and Brand Protection
- High‑security DOVIDs (e‑passports, banknotes) – CGH generates complex, non‑reproducible diffractive structures that are extremely difficult to counterfeit.
- Machine‑readable holograms – Embedded digital codes that can be scanned and verified by automated readers at borders or checkpoints.
- Tax stamps & excise seals – CGH can create unique, batch‑specific diffractive patterns that are impossible to reverse‑engineer.
- Forensic features – Nanotext and microtext embedded within the CGH structure, readable only under high magnification.
- 3D display holograms (retail, museums) – Real‑time CGH projected via SLMs for interactive exhibits.
🌍 Holoseal’s Role in CGH Hologram Production
Holoseal does not perform CGH algorithm development in‑house. However, we partner with specialised origination houses that use advanced CGH software and e‑beam or dot matrix writers to create custom masters. We can help clients translate their security requirements (e.g., unique diffractive codes, hidden images, machine‑readable data) into a CGH design, then manage master origination, electroforming, and mass embossing. With 15+ years of experience, we ensure that the CGH pattern is optimised for both security and manufacturability.
❓ Frequently Asked Questions About Computer Generated Holograms
- Is a CGH more secure than an optical hologram? – Generally, yes. Because the design is algorithmic and can be kept secret, and the complexity can be much higher (e.g., encrypted data embedded in the fringe pattern). However, a well‑made optical DOVID is also very secure.
- Can a CGH be mass‑produced by embossing? – Yes – once the master is written, it can be electroformed and embossed exactly like an optical hologram. Millions of copies can be made.
- What software is used to create CGH? – Specialised software such as LightTrans VirtualLab, Optiwave, or custom MATLAB/C++ scripts using FFT and Gerchberg‑Saxton algorithms.
- Do CGH masters cost more than optical masters? – Yes, due to the computational design time and often higher‑resolution writing (e‑beam). However, for complex, high‑security features, the added cost is justified.
- Can I see a CGH with the naked eye? – Yes – after embossing and metalization, a CGH‑originated hologram looks exactly like a traditional hologram. The diffractive effects (rainbow colours, depth, kinetic motion) are visible by tilting.
- How to order CGH‑based hologram labels from Holoseal? – Provide your desired visual effects and any machine‑readable data requirements. We will work with our CGH partners to design the diffractive structure, create a master, and produce finished labels. Contact us for a quote.
