LoCAte Focus Analyser ('beta')

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Load and analyse a sample image file:

Load and analyse your own image file:

Image is gamma-encoded

Also, have a look at the gallery of contributed results.

Longitudinal chromatic aberration ('LoCA') can cause the best-focus distance of a stereomicroscope or macro lens to differ for each camera colour channel (red, green, blue), causing image degradation. Use this web page tool to explore how well your equipment's optics focuses the three colour channels.

Analyse a sample image, or create a test image using your own equipment and then load and analyse it.

Loading ...

Analysis of abc.png

Edge locators (left and right), and image overview (center)

Width:0000 px
Height:0000 px
FOV: mm wide
Incline: degrees
Edge slant: °
Image: 16-bit linear, 0x3FFF

Enter a negative incline if left end is highest.

Drag the yellow rectangles and triangles to identify the edge. Drag the blue rectangle to move the view region.

x:0000px, z:245μm

Edge spread distance (between the 10% and 90% levels)
vs. position along horizontal FOV / focal distance

Edge spread (pixels; target μm)

version info date time

Position along horiz FOV (pixels; target μm); focal distance (μm)


Smoothing window px (px on each side)

Edge profile at cursor
(x: px)

Pixel value (linear RGB)

Position within the cursor gap (pixels)

Spreads: , , px

All Red Green Blue

'White/black' illumination levels
vs. position along horizontal FOV

Pixel value (linear RGB)

Position along the horizontal FOV

Image histogram

Freqency (log scale)

LoCAte keeps settings in local storage. Clear settings for this image or all images.

Pixel [1234,5678]
rgb8 [44,44,44]
rgb16 [4444,4444,4444]

What can you do with LoCAte?

Evaluate optics: Best photos will come from microscopes and lenses with minimum chromatic aberration and high resolution. Use LoCAte to get a feel for these parameters, using just one photo of an inclined target.

Measure depth of field: Using an inclined target, information provided by LoCAte can help plan depth of field (DOF) increments when doing focus bracketing.

Check focus bracketing intervals: Take a series of focus-bracketed photos of an inclined target and use LoCAte to check the focus offset between photos. Example.

Investigate sharpening algorithms: Create a synthetic edge image, sharpen it, and then use LoCAte to analyse the result, to see how sharpening varies with degree of edge spread (blur), and how it affects the image and edge profile.

Creative Commons License
LoCAte Focus Analyser by Jim Elder is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Citation info:
LoCAte Focus Analyser 'beta' (2017-Jan)
Jim Elder, Ottawa, Canada

Disclaimer: Please be aware that this isn't a professional tool or service; I'm just sharing something I made for my own use. There's no assurance that it works as described or intended, ie., it may have bugs and/or errors.

Comments or suggestions