SAED or Ring Pattern Image Analysis Platform

ChemFitX provides an online selected-area electron diffraction (SAED) and diffraction-ring image analysis workflow for researchers working with TEM diffraction patterns from crystalline, nanocrystalline and polycrystalline materials. The platform combines diffraction-center selection, ring measurement, d-spacing calibration, radial-intensity analysis, automated ring detection, reciprocal-space calculations, phase-assisted hkl matching and optional 3D crystal-structure visualization in one browser-based workspace.

Upload a SAED or TEM diffraction image, set or automatically estimate the diffraction center, calibrate the ring pattern using a known reference ring or camera geometry, and then measure rings manually or detect them automatically from the radial intensity profile. ChemFitX reports calibrated d-spacing together with reciprocal-space and ring-quality descriptors that can be used to inspect the diffraction pattern before any crystallographic interpretation.

The uploaded diffraction image and optional CIF reference files are read and analyzed locally in your web browser by this application. They are not uploaded to ChemFitX servers during the analysis.

What the SAED and Ring Pattern Analysis Platform Can Do

Import diffraction images in TIFF/TIF, PNG, JPG/JPEG and BMP formats.
Set the diffraction center manually or estimate the transmitted-beam center automatically from the image.
Measure diffraction-ring radii manually from the selected center.
Automatically detect ring candidates from a radial intensity profile calculated from the original image pixels.
Calibrate diffraction d-spacing from a known reference ring using K = Rref × dref.
Use an alternative camera-geometry calibration based on accelerating voltage, relativistic electron wavelength, effective camera length and detector pixel size.
Calculate d-spacing for each calibrated diffraction ring.
Calculate reciprocal spacing g = 1/d and scattering-vector magnitude q = 2π/d.
Estimate relative ring intensity, peak signal-to-noise ratio, ring-profile FWHM, reciprocal-width Δg and (R/R1)² values.
Apply Gaussian, moving-average or Savitzky-Golay smoothing to the radial profile used for ring detection.
Adjust auto-detection sensitivity, center exclusion, minimum ring separation and maximum number of detected rings.
Display and customize diffraction-ring labels, colors, opacity, line width and line style.
Inspect the radial intensity profile together with measured and detected rings.
Upload one or more CIF reference structures for phase-assisted hkl matching.
Create a manual crystallographic reference from unit-cell parameters, fractional atoms and optional symmetry operations.
Rank supplied reference phases by consistency with the experimental d-spacings.
Generate candidate hkl assignments for calibrated rings using the supplied crystal structure or lattice.
Use a Z-weighted structure-factor proxy to help suppress extinct or very weak candidate reflections when atomic coordinates are available.
Visualize a selected crystal structure interactively in 3D with ball-and-stick, space-filling or atoms-only display modes.
Repeat the unit cell along a, b and c for supercell visualization without changing the underlying lattice geometry.
Export the annotated diffraction image, numerical ring results, phase-matching results and hkl-indexing information.

Supported Diffraction Images and Input Requirements

Supported image formats

The platform accepts TIFF/TIF, PNG, JPG/JPEG and BMP images. For quantitative ring measurements, use the original diffraction image whenever possible. Rescaling, cropping, interpolation or lossy compression can change ring radii or degrade weak features, especially when camera-geometry calibration is used.

A reliable diffraction center

Ring radii are measured from the diffraction center. The center can be selected manually or estimated automatically from the brightest local region. Automatic centering is a starting estimate and should be checked visually because beam stops, saturation, asymmetry, texture, off-center illumination or strong diffraction spots can bias the apparent center.

A valid d-spacing calibration

Physical d-spacing values require either a known reference ring or a justified camera-geometry calibration. Without a valid calibration, ring radii remain pixel measurements and should not be interpreted as absolute d-spacings.

SAED d-Spacing Calibration

Reference-ring calibration

Reference-ring calibration is the recommended workflow when one diffraction ring has a reliably known d-spacing. Measure the reference ring, enter its known d-spacing in angstroms and select that ring as the reference. ChemFitX calculates the camera constant in pixel-angstrom units using K = Rref × dref. Other measured ring spacings are then calculated from d = K/R.

This approach is internally tied to the pixel dimensions of the uploaded image. If the diffraction image has been resized after acquisition, the calibration remains valid only when the reference ring is measured in that same resized image.

Camera-geometry calibration

Camera-geometry calibration uses accelerating voltage, the corresponding relativistic electron wavelength, effective camera length and detector pixel size. ChemFitX calculates the electron wavelength from the entered accelerating voltage. For example, the platform uses approximately 0.025079 Å at 200 kV, equivalent to 2.5079 pm or 0.0025079 nm.

Geometry-based calibration should use the original, unrescaled diffraction image and acquisition-specific camera parameters. Nominal microscope camera length can differ from the effective calibrated camera length, so a reference-standard calibration is generally preferable when high accuracy is required.

Manual and Automatic Diffraction-Ring Measurement

Manual ring measurement

After setting the diffraction center, choose the ring-measurement tool and select the radius of a visible diffraction ring. The platform stores the ring radius in pixels and, when SAED calibration is available, converts that radius to d-spacing.

Automatic ring detection

Auto-detection analyzes radial image intensity around the selected center. The central transmitted-beam region is excluded, the radial profile can be smoothed, and local ring-like maxima are selected according to the chosen detection sensitivity and minimum ring separation.

Automatic detection is intended to identify candidate rings, not to replace visual inspection. Diffuse halos, spotty rings, preferred orientation, overlapping rings, beam-stop shadows, detector artifacts and strong single-crystal spots can produce maxima that do not correspond to independent powder-like reflections.

Radial Intensity Profile

The radial intensity profile summarizes image intensity as a function of distance from the selected diffraction center. Peaks in this profile can correspond to diffraction rings, while peak width and prominence provide additional information about how sharply the ring is expressed in the image.

The platform offers Gaussian, moving-average and Savitzky-Golay smoothing for the radial profile. Smoothing is intended to stabilize ring detection and visualization. Use the minimum amount needed, because excessive smoothing can merge nearby rings, suppress weak features or alter apparent peak widths.

Display adjustments versus quantitative analysis

Brightness, contrast and threshold controls are display aids. The platform’s ring detection and radial-intensity calculations use the original uploaded image pixels, so visual enhancement does not silently replace the source data used for quantitative ring analysis.

Derived SAED Quantities

d-spacing

The calibrated d-spacing represents the real-space lattice-plane spacing corresponding to the measured diffraction-ring radius under the selected calibration. Its accuracy depends directly on center selection, ring-radius measurement and calibration quality.

Reciprocal spacing g

ChemFitX reports g = 1/d in Å⁻¹. This is the reciprocal-lattice magnitude associated with the measured d-spacing.

Scattering-vector magnitude q

The platform also reports q = 2π/d in Å⁻¹. Because some diffraction and scattering literature uses g while other sources use q, both values are shown explicitly to avoid ambiguity.

Relative intensity and peak SNR

Relative intensity is derived from the radial-profile peak strength and is intended for within-image comparison. The peak signal-to-noise ratio provides an additional indicator of how clearly a radial feature stands above its local background or noise.

Ring FWHM and Δg

The radial peak FWHM is reported in pixels, and the platform can derive a reciprocal-width estimate Δg when the pattern is calibrated. These values describe ring-profile broadening in the processed radial representation; they are not automatically converted into crystallite size, strain or instrumental broadening without an appropriate diffraction-broadening model and calibration.

(R/R1)² ratio

The squared radius ratio (R/R1)² compares each ring radius with the first measured ring. For some simple powder patterns this ratio can be a useful qualitative consistency check, but it is not a universal indexing rule for arbitrary crystal structures or multiphase materials.

Phase-Assisted hkl Indexing with CIF Reference Structures

The advanced crystallography workspace is optional. It is intended for cases where a user has one or more plausible reference structures or known crystallographic information and wants to compare measured SAED d-spacings with calculated reflections.

Loading multiple candidate CIF phases

Multiple CIF reference files can be loaded and ranked. The platform parses unit-cell parameters, available space-group metadata, atomic coordinates and symmetry operations locally in the browser. A selected phase can then be used for reflection generation, hkl matching and 3D visualization.

Manual crystallographic reference

If a CIF is not available, a manual reference can be created by entering a phase name, optional space group, the six unit-cell parameters a, b, c, α, β and γ, fractional atomic coordinates and optional symmetry operations. The reciprocal-lattice calculation uses the full unit-cell metric, so triclinic, monoclinic, orthorhombic, tetragonal, trigonal/rhombohedral, hexagonal and cubic metrics can be represented.

Reflection generation

Candidate reflections are generated within user-defined Miller-index and d-spacing limits. Centering conditions are applied from recognized lattice symbols when available. If atomic coordinates are present, the platform can use a Z-weighted F² proxy to help suppress candidate reflections that are extinct or very weak in the simplified model.

Phase-consistency ranking

Each supplied reference phase is compared with the experimental calibrated d-spacings using a user-defined matching tolerance. ChemFitX reports the number of matched rings, coverage, RMS d-spacing error and a consistency score.

The ranking is a screening aid, not proof of phase identity. Different structures can share similar d-spacings, and real SAED patterns can contain multiple phases, texture, double diffraction, dynamical effects or incomplete rings. A high consistency score should therefore be evaluated together with chemistry, morphology, independent diffraction data and appropriate crystallographic evidence.

Candidate hkl Assignments

For a selected reference phase, the platform compares each measured d-spacing with calculated reflection groups and lists candidate hkl values within the chosen tolerance. It reports experimental d, calculated d, relative error, candidate Miller indices, the simplified F² proxy and a qualitative match assessment.

A single ring can correspond to several symmetry-equivalent or nearly coincident reflections, so multiple hkl candidates may be shown. The first listed candidate should not be treated as a definitive crystallographic assignment without considering the complete diffraction pattern and the reference structure.

Interactive 3D Crystal Structure Viewer

When atomic coordinates are available, ChemFitX can display the selected reference structure interactively in three dimensions. The viewer supports ball-and-stick, space-filling and atoms-only styles, perspective or orthographic projection, unit-cell display, bonds, atom labels, crystallographic axes and optional auto-rotation.

Users can change atom size, bond radius, bond-distance cutoff, unit-cell edge width, background color, bond color and element appearance. The structure can also be repeated along a, b and c to display a supercell. These settings alter visualization only; they do not change the underlying unit-cell geometry or diffraction calculations.

The 3D viewer can export a PNG image for figures or records. It is a visualization of the supplied crystallographic model, not a crystal-structure solution performed from the uploaded SAED image.

Ring Customization and Annotated Image Export

Measured rings can be customized individually so that different reflections are easy to distinguish on the diffraction image. Available controls include ring color, opacity, line width and line style. Calibrated d-spacing and phase-assisted hkl labels can be displayed on the image when enabled.

The image-export workflow can save an annotated version of the diffraction pattern. Use annotations conservatively in publication figures and retain an unmodified original image for traceability.

How to Use the ChemFitX SAED Analysis Tool

Upload a SAED or TEM diffraction image in TIFF/TIF, PNG, JPG/JPEG or BMP format.
Set the diffraction center manually, or use Auto Center and verify the estimated center visually.
Choose the SAED calibration method. For reference-ring calibration, measure a known ring and enter its d-spacing. For geometry calibration, enter the acquisition-specific accelerating voltage, effective camera length and detector pixel size.
Measure visible diffraction rings manually or run Auto-Detect Rings to identify candidate radial peaks.
Inspect the radial intensity profile and adjust smoothing, sensitivity, center exclusion and minimum ring separation only when needed.
Review the measured ring radii, calibrated d-spacings and derived g, q, relative-intensity, SNR, FWHM and radius-ratio values.
Correct or remove questionable rings before crystallographic interpretation.
If phase-assisted indexing is needed, open the Advanced Crystallography section and upload one or more plausible CIF structures or create a manual reference cell.
Set the d-match tolerance and reflection limits, then run Match / Index.
Review the phase-consistency ranking and per-ring hkl candidates. Treat these results as reference-assisted screening rather than automatic phase proof.
Use the interactive crystal viewer when atomic coordinates are available and customize the display if a structure figure is needed.
Export the annotated image and numerical results to the required format.

Exporting SAED and Ring Analysis Results

Excel

Excel export can include ring measurements, SAED calibration parameters and derived quantities. When advanced crystallography has been used, the workbook can also include phase-matching and hkl-indexing results.

CSV

CSV export provides a tabular record of the diffraction-ring analysis, including ring number, source, radius, d-spacing, g, q, relative intensity, SNR, FWHM, reciprocal-width information, radius ratio and ring styling information.

JSON

JSON export provides structured analysis data that can be stored or parsed programmatically.

Image and structure PNG

The diffraction-image export saves the current annotated pattern, while the advanced 3D viewer can export the displayed crystal structure as a PNG.

Data Privacy and Browser-Based Processing

The SAED image and optional CIF reference files are processed locally in the browser by this platform. The application does not upload these research files to ChemFitX servers during analysis.

Users should still follow their institution’s policies for unpublished microscopy data, confidential structures, shared computers, browser storage and downloaded exports.

Scientific Scope and Limitations

Reliable d-spacing requires accurate center selection and a valid diffraction calibration.
Automatic center estimation should be checked visually, particularly for saturated beams, beam stops, asymmetric patterns or strong off-center reflections.
Automatic ring detection identifies radial-intensity maxima and can be affected by diffuse scattering, overlapping rings, spotty rings, preferred orientation, image artifacts and noise.
Reference-ring calibration depends on the correctness of the known reference d-spacing used to establish the camera constant.
Camera-geometry calibration depends on acquisition-specific effective camera length, detector pixel size, accelerating voltage and an unrescaled image.
The relativistic electron wavelength is calculated from accelerating voltage; at 200 kV the platform value is about 0.025079 Å, not 0.0251 nm.
Radial relative intensity is not a quantitative electron-diffraction structure-factor intensity and should not be interpreted as such.
The Z-weighted F² value used in advanced indexing is a simplified proxy, not a quantitative simulation of electron-diffraction intensity.
Phase-consistency scores rank only the supplied reference structures and do not establish that the top-ranked phase is uniquely correct.
hkl assignments are reference assisted and can remain ambiguous when several reflections have similar d-spacings.
Space-group symbols alone do not reproduce every screw/glide extinction rule in a manual phase; explicit symmetry operations are needed when those rules are important.
SAED intensities can be strongly influenced by dynamical diffraction, specimen thickness, orientation, multiple scattering and experimental geometry.
Ring-profile FWHM or Δg should not be converted directly into crystallite size or strain without a validated broadening model and instrumental contribution.
A 3D structure displayed from CIF coordinates is a visualization of the supplied reference structure, not a structure solved from the SAED image.
Image display adjustments do not replace careful acquisition, calibration and scientific interpretation.

Frequently Asked Questions

What is SAED analysis?

Selected-area electron diffraction analysis examines diffraction spots or rings recorded in a TEM to obtain reciprocal-space and crystallographic information from a selected specimen region.

Can ChemFitX calculate d-spacing from a SAED ring pattern?

Yes. After the diffraction center and SAED calibration are established, ChemFitX converts measured ring radii into d-spacing values.

Which image formats can I upload?

The platform accepts TIFF/TIF, PNG, JPG/JPEG and BMP diffraction images.

What is the recommended SAED calibration method?

A known reference ring is generally the most direct workflow in this platform because it establishes the pixel-based camera constant from a ring with a justified d-spacing. Geometry calibration is also available when reliable acquisition parameters are known.

What electron wavelength does the platform use at 200 kV?

The platform calculates the relativistic wavelength from accelerating voltage. At 200 kV it is approximately 0.025079 Å, which is 2.5079 pm or 0.0025079 nm.

Can ChemFitX automatically find the diffraction center?

Yes, it can estimate the center from the bright central region. The result should be checked visually before quantitative ring measurement.

Can the platform automatically detect diffraction rings?

Yes. Auto-detection searches the radial intensity profile for candidate ring peaks after excluding the central beam region. Detected rings should be reviewed before use.

What are g and q in the results?

ChemFitX reports g = 1/d and q = 2π/d. Both are reciprocal-space quantities, but they use different conventions.

Does the platform automatically identify a crystal phase?

No. The advanced module compares measured d-spacings with reference structures supplied by the user and ranks their consistency. This is phase-assisted screening, not definitive automatic phase identification.

Can I upload multiple CIF files?

Yes. Multiple candidate CIF structures can be loaded and ranked against the experimental d-spacings.

Can I enter crystallographic data without a CIF?

Yes. A manual reference can be created from the six unit-cell parameters, optional space group, fractional atoms and optional symmetry operations.

Does ChemFitX support non-cubic crystals?

Yes. The crystallographic engine uses the general lattice metric, so it can represent triclinic through cubic unit cells rather than forcing a cubic approximation.

Are the calculated hkl values definitive?

No. They are candidate assignments based on the supplied reference structure, d-spacing tolerance and implemented reflection filters. Multiple candidate reflections may correspond to one ring.

What is the F² proxy?

When atomic coordinates are available, ChemFitX uses a simplified atomic-number-weighted structure-factor proxy to help screen reflections. It is not a quantitative electron-diffraction intensity calculation.

Can I visualize the crystal structure in 3D?

Yes. A loaded structure with atomic coordinates can be shown in an interactive 3D viewer with configurable display style, projection, bonds, unit cell, labels, axes and supercell repeats.

Are my SAED images or CIF files uploaded to ChemFitX?

For this application, the diffraction image and CIF files are read and processed locally in the browser and are not uploaded to ChemFitX servers by the analysis code.

Can I export the results?

Yes. The platform provides numerical exports including Excel, CSV and JSON, annotated diffraction-image export, indexing export, and PNG export from the 3D structure viewer.

Scientific References

Williams, D. B.; Carter, C. B. Transmission Electron Microscopy: A Textbook for Materials Science. Springer.
Reimer, L.; Kohl, H. Transmission Electron Microscopy: Physics of Image Formation. Springer.
Fultz, B.; Howe, J. M. Transmission Electron Microscopy and Diffractometry of Materials. Springer.
International Tables for Crystallography, Volume A: Space-Group Symmetry. International Union of Crystallography.