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You are here: Home / The Last Word / Presenting capture accuracy results: the basics

Presenting capture accuracy results: the basics

January 7, 2016 JimK 3 Comments

This is the fourteenth in a series of posts on color reproduction. The series starts here.

I am writing Matlab code to automate the crunching and presentation of camera captures of Macbeth color checker charts. The purpose is to provide a way to test capture and raw developer accuracy. I’ve written code that does the basic analysis, I’m working on how to present the data. Today, I’ll show you what I’ve done so far.

The camera and the raw developer that I used to get the data shown here don’t matter in this context, so I’m not going to address that issue,

First, a plot of the CIELab Delta-E for each patch:

mac cc de

I’ve shaded the columns so that they’re about the same color as the patches. Like that?

Now, a look at just the chromaticity errors, also in Lab:

mac cc dab

Hmm. The upper right corner is obscured by the two yellowish patches. In Matlab, you can rotate the graph to see what’s going on there, but I can’t post the interactive graphs on the web. I think varying the viewing angle with each graph would be confusing.

Now, a look at the chromaticity errors in more detail in Lab:

mac cc ab

I’ve pinned the axis range to [-100, 100] for both axes. That means that plots are easy to compare, but reduces the magnification from what would be available if I fitted the ranges tightly for each plot.

Here’s the same data in Luv:

mac cc uv

Whether you like Lab or Luv for this probably depends on your level of familiarity with each. I’ll probably use Lab mostly, since photographers tend to be more comfortable with it.

I will also be looking for some overall scalars that represent important qualities, such as color twist. Those will be useful for comparing sets of captures or developments with different cameras, processors, or lighting.

Comments are welcome.

The Last Word

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Comments

  1. N/A says

    January 7, 2016 at 10:06 am

    may be reproduce the work of Sandy Mc (dcptool) with visualizing the twists (if present) in DCP & ICC profiles… he did nice 2d view of 3rd object

    Reply
  2. N/A says

    January 7, 2016 at 10:10 am

    > but I can’t post the interactive graphs on the web.

    make it totally 2d – lined in just one line or may be circle-wise (color circle), no need to keep 24 patches arranged in the same order… color circle can keep close colors close to each other better than a linear view…

    Reply
    • N/A says

      January 7, 2016 at 10:12 am

      https://thecolourguru.files.wordpress.com/2011/02/1186979307_h2o_colorwhl_p5_hr.jpg

      like greater radius for a segment present greater deviation (according to whatever metrics)

      Reply

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