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Accueil / Case studies / Colour appearance on a bottle cap
Application study · Packaging components

Bottle-cap colour appearance: reduce lighting variation before comparing the surface

The source colour capture shows a yellow cap-like face with a lighter region on one side. A thin flat coaxial light is the demonstrated illumination; a new trial still needs controlled exposure and colour processing before assigning a colour limit.

Control the colour recipe before turning a lighter patch into a reject decision.

  • Light in sourceLS-FCS50 · white
  • EvidenceReal application-lab image
  • Imaging kitCamera, lens and fixture proposed
  • AcceptanceValidate on representative parts
3D view of the inspection set-up: camera, lens, light and partDrag to rotate · scroll to zoom
3D illustration · real CAD where available
Walk through this setup 5 guided stops
From component to inspection

Understand each choice.

Choose a stop to frame the part in 3D and see why it belongs in this setup. The component notes and links remain available if 3D cannot load.

Camera and available lens CAD are published models. Lens and light envelopes use printed dimensions. The linked station uses its published base size and column height; carriage, brackets, fittings, parts and spacing are illustrative. Confirm load, travel, fasteners and clearances before ordering. Light paths explain the arrangement and do not simulate optical performance. Representative part geometry is illustrative, not reconstructed inspection evidence. The specimen and lighting angle are representative, not dimensions or settings recovered from the source capture.

From the demo to your test bench

Build around the parts you can buy.

Explore each component, check its specifications and compare alternatives. The proposed quote includes the linked test station; its catalog listing includes two lighting holders.

Mount the optics with intent

The station is an optical test bench, with its two lighting holders included in the catalog listing. The 3D column and base follow the published height and footprint. Carriages, clamps and part supports are schematic: confirm camera screw pattern, lens support, light fasteners, permissible load and actual travel before ordering.

Configure the mounting station →

Complete the electrical system

Select a controller against the exact light voltage, drive mode and power, then confirm camera data/power/I/O cables and a suitable PC. These are not silently added to the proposed optical kit.

Lighting application-lab catalog capture

Evidence you can inspect

Visible in the images

A lighter region is visible against the yellow circular face.

What the source reports

The source labels the image bottle-cap surface colour-difference inspection with the white LS-FCS50.

How to use this evidence

One uncalibrated colour image, without a numerical colour difference, accepted/rejected sample labels or lighting/camera repeatability data.

What the camera saw

Cropped from the source test sheet; original test annotations are retained. Captures are not generated or enhanced. Drag the comparison slider or use the image buttons.

Source white flat-coaxial capture: a lighter surface region is visible on the right of the yellow circular face.
Source white flat-coaxial capture: a lighter surface region is visible on the right of the yellow circular face.

The challenge

Apparent colour changes with highlights, exposure and white balance as well as the material itself.

Curved geometry can create local illumination changes that resemble a material difference.

How it was solved

The source identifies the white flat coaxial light for bottle-cap colour-difference inspection. It does not supply calibrated colour values or classify the light patch.

Use a proposed colour camera and the narrower macro field for a representative cap sample. Keep the illustrated viewing field within the 50 mm light-guide region and confirm glare on the real part.

Why it works

  1. 1

    The thin light-guide arrangement provides a source path to try when uniform reflected appearance matters and mounting space is limited.

  2. 2

    A visible lighter region is not a quantified colour difference or proof of a material defect.

From image contrast to a production decision

What to validate on your part

A useful sample image is the starting point. These are the checks that turn the concept into a defensible inspection.

  1. 01

    Stabilize the camera recipe

    Fix exposure, white balance and colour processing, and use a suitable reference if numerical colour acceptance is required.

  2. 02

    Include normal surface variation

    Test curvature, mould finish, permitted gloss and accepted colour batches.

  3. 03

    Validate the acceptance limit

    Compare labelled surface differences under repeatable geometry and record false calls.

Explore your inspection requirements

How many pixels cover your feature?

Compare feature coverage, camera pixel requirements and exposure using your own planning inputs. These are calculated planning values, not inspection results or an accuracy specification.

Editable planning scenario. Adjust these example inputs for your application; they are separate from the source test and 3D setup. Motion allowance and target coverage are starting points to validate, not acceptance limits. Pixel count starts from the proposed camera's catalog resolution.

Object sampling0.04085 mm/px
Pixels across feature12.24 px
Horizontal pixels for target1000 px
Motion during exposure0.2448 px
Exposure ceiling from motion204.2 µs
Formulas and assumptions

The field, feature, speed and exposure start with neutral example values. They are not taken from the source test or the 3D illustration. Allowed motion starts at an editable 0.5-pixel example; it is not a recommended acceptance limit. Target coverage starts at an editable 5-pixel example; it is not a recommended detection or measurement threshold. The horizontal pixel count starts from the catalog Resolution row for MV-CS050-10GC. Use the effective width after cropping, binning or decimation if those modes are enabled.

  • Object sampling (mm/px) = field width (mm) / horizontal pixels.
  • Pixels across feature = feature width (mm) / object sampling (mm/px).
  • Horizontal pixels for target = field width (mm) × target pixels across feature / feature width (mm), rounded up to a whole pixel.
  • Motion (px) = speed (mm/s) × exposure (µs) / 1,000,000 / object sampling (mm/px).
  • Exposure for allowed motion (µs) = allowed motion (px) × object sampling (mm/px) / speed (mm/s) × 1,000,000.

The exposure result is the maximum duration from this motion allowance alone. At zero speed, motion sets no exposure limit; the camera, lighting, saturation and other constraints still apply. A shorter exposure does not itself guarantee a reliable inspection.

Field width and feature width refer to the same object plane. The motion calculation assumes uniform linear motion parallel to the field-width direction and a single exposure. It does not model perspective, vibration, rolling-shutter distortion, diffraction, defocus or optical distortion. A strobe may change the effective exposure.

The target result is a horizontal sampling requirement, not a camera recommendation or a change to the selected camera. It uses the effective image width after cropping, binning or decimation and does not determine the vertical resolution or sensor size. Pixel coverage alone does not establish detectability or measurement accuracy. Validate contrast, lens performance, working distance, illumination, calibration, camera exposure limits and the inspection algorithm on representative parts. Changing field width does not change the 3D model or certify that the proposed lens can achieve that field.

The set-up and the parts

Tested lightLS-FCS50, white
Source camera / lensNot specified in the source image caption; proposed parts below
Proposed lens point0.25x at 150 mm, printed lens pair
Derived proposed field33.7824 × 28.2624 mm = sensor dimensions / 0.25x; not a source test field
Light-guide area (printed)50 × 50 mm
Housing (printed)90 × 90 × 10 mm
Optical arrangementCamera views through the transmissive flat light-guide region; verify on the actual sample
Mounting (proposed)LS-BT-XZ-G-6-6045; 600 mm column, 600 × 450 mm base, glass tray and two included lighting holders

"Tested" identifies the part named in the source. "Our pick" is a proposed alternative or supporting part. The quote includes only cards marked "In proposed setup", with the quantities shown; other test arrangements are separate. Confirm colour, optics, controllers, power supplies, cables and mounting before ordering.

About this case study: the photos and camera images come from the application laboratory of the maker of the lighting and optics we sell, imaged on the parts shown; your results depend on your part, camera and set-up. This is an application-lab study, not a LumaSpec customer deployment. Source figures are reported results; proposed components require a fresh trial. The 3D scene illustrates the arrangement and does not simulate imaging performance.

More case studies

Start with your inspection requirement

Make the next trial specific.

Tell us the part size, smallest defect or tolerance, available working distance, material and line speed. Include what a good part and a reject look like.

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