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Frequently Asked Questions


How much does ImageZebra cost?

ImageZebra is free to try. Contact for more information.

How do I get help?

We would love to help you out. Contact us at

Using ImageZebra

Can I place multiple test targets in a single image to upload and analyze?

Not at the moment. Currently we only support a single test target per image.

What targets are supported?

See the list of supported test targets for all currently supported targets.

Can I use my own custom reference values?

This feature is on the list of new upcoming features. We hope to announce this ability soon!

I want to use the M-19-21 specification. Do you support that?

Yes! The FADGI 2023 specification calls this "FADGI 2023 Modern Textual Records". This is identical to the M-19-21 specification.


Why could I see differences in the results between ImageZebra and another tools, like

There are a few reasons a direct comparison could lead to apparently discordant results:

  • The name of the metrics is not consistent between the two tools. ImageZebra uses terminology as defined by FADGI.
  • does not test and report all the FADGI metrics available on the Golden Thread test pattern. Below is a list of the missing metrics not available with

    • OECF (Tone Response) - not measured in either colorimetric (L*) or digital counts
    • White Balance Error - not measured in either colorimetric (L*) or digital counts
    • Resolution - FADGI guidelines have established resolution limits with star ratings. measures the resolution but does not report the star rating
  • Some metrics are only partially implemented on

    • Noise (digital counts) - Noise measurement in units of digital counts is not available, however the Noise measurement in colorimetric units (delta L* Stdev) is available
    • Reproduction Scale Accuracy – measures the actual resolution of the scanned image, however, it does not summarize the FADGI star rating for this measurement. The summary report can be misleading when the metric is not assigned a star rating and reported with the other metrics.
  • uses the average SFR response of the 5 locations to determine the FADGI star rating. ImageZebra and Golden Thread both report summaries including worst star rating from all locations. The average value (as reported by could be misleading, and is less sensitive to issues with individual patches.

  • There is also a concern about the size of the analysis region used by, as well as differences in location where the two tools make their exact measurements. It is possible the small ROI could be giving inaccurate results.
  • Color Accuracy: ImageZebra currently uses the worst color patch for the summary star rating. However, this will change in the next release to be consistent with and Golden Thread software, which computes the Average dE color error of all color and neutral patches before determination of the star rating.
  • ImageZebra does not currently measure the color to color misregistration. It is unclear whether is using the very small ROI’s which it displays on the image. If so, there could be a large error source in the accuracy of the color registration metric. appears to report the average color misregistration in the summary.
  • is no longer actively supported and no longer participates in any ISO standards.

Error messages

I am getting an error that says “Target could not be identified”. What can I do to fix this?

There are several reasons for this error message:

  1. The image did not contain a valid test target. See the list of supported test targets.
  2. The image is defined using 8 bits per pixel. Only 24 and 32 bit per pixel images are supported.
  3. The test target was cropped off. It is important that the entire test target be captured in the image
  4. The color or brightness of the image is too far off.

I am getting an error that says “Target could not be identified. This may be because the image is low resolution (MN pixels)”. What can I do to fix this?

The image was not high enough resolution. The patches in the test target need to be at least 25 ✕ 25 pixels. That means the test targets themselves need to be at least the following size:

  1. Golden Thread Device Level: 800 ✕ 1,200 pixels
  2. Golden Thread Object Level: 1,000 ✕ 100 pixels
  3. ColorChecker SG: 1,500 ✕ 1,000 pixels