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doc:appunti:software:colorchecker_clones [2020/01/12 06:54] – [Applying the style in Darktable] niccolodoc:appunti:software:colorchecker_clones [2020/01/27 12:20] (current) – [Solid Pigments vs Offset Printing and Dithering] niccolo
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-====== The ColorChecker and its Clones ======+====== The Grey White Balance Colour Card: an X-Rite clone ======
  
-{{.:color_management:colorchecker_gretag-macbeth.jpg?360 |https://commons.wikimedia.org/wiki/File:Gretag-Macbeth_ColorChecker.jpg}}+**GWBCC** is a series of products manufactured by an **[[https://www.greywhitebalancecolourcard.co.uk/|UK company]]**; they are **[[wp>ColorChecker|color checkers]]** to be used in photographic color calibration. They have a certain notoriety for the fact that they cost half or a quarter of other much more famous products. In March 2019 I purchased for about 22 € the **2in1** model, a 140x88 mm plastic card which has the **24 color swatches** on one side and a **three grays** target on the other. 
 + 
 +Here I share my experience using that card to do **color calibration** of **photographies** and images acquired using a **scanner**. The workflow is entirely based on free and open source software: **Debian GNU/Linux** operating system, **The GIMP** as image processing software and **Darktable** for color calibration. 
 + 
 +The final word is: despite **the product lacks a real color calibration**, some results can be obtained at the cost of **a lot of preparatory work**, but without any claim of objective precision. 
 + 
 +===== The ColorChecker and its Clones ===== 
 + 
 +[{{.:color_management:colorchecker_gretag-macbeth.jpg?360 |The original Gretag Macbeth ColorChecker. Photo from [[https://commons.wikimedia.org/wiki/File:Gretag-Macbeth_ColorChecker.jpg|wikimedia.org]]}}]
 The **[[wp>ColorChecker]]** is a registered trademark of a [[wp>Color chart|color chart]] introduced in 1976 and manufactured by **Macbeth**, now **X-Rite**; it features **24 squared patches** of various colors. The colors were choosen quite arbitrarly: six **shades of gray**, some **primary colors**  (red, green, blue, cyan, magenta, and yellow) and other colors of natural objects, like skin tones, foliage, etc. The **[[wp>ColorChecker]]** is a registered trademark of a [[wp>Color chart|color chart]] introduced in 1976 and manufactured by **Macbeth**, now **X-Rite**; it features **24 squared patches** of various colors. The colors were choosen quite arbitrarly: six **shades of gray**, some **primary colors**  (red, green, blue, cyan, magenta, and yellow) and other colors of natural objects, like skin tones, foliage, etc.
  
 There are several manufacturers that sell **similar (cloned) color charts**; they are **more or less compatible** with the X-Rite original, where compatibility is measured on the precision obtainable using the same software procedures calibrated on the X-Rite product. The price and quality vary widely; durability of the materials, uniformity and consistency of the colors and printing method are the distinctive features. There are several manufacturers that sell **similar (cloned) color charts**; they are **more or less compatible** with the X-Rite original, where compatibility is measured on the precision obtainable using the same software procedures calibrated on the X-Rite product. The price and quality vary widely; durability of the materials, uniformity and consistency of the colors and printing method are the distinctive features.
  
-===== The Grey White Balance Colour Cards =====+===== Solid Pigments vs Offset Printing and Dithering =====
  
-The most inexpensive color charts are obtained by **[[wp>Offset printing|offset printing]]**, the color patches are not made from solid color pigments, but obtained using **dithering** and **halftoning** of the primary printing colors. The following close-up are taken from the **The 2 in 1** checker, manufactured by **[[https://www.greywhitebalancecolourcard.co.uk/|Grey White Balance Colour Cards]]**; you can see how the patches are obtained with dithering, in particular the second photo shows the **grey patches** on the left: they are made by a **white background with black dots** over it:+The most inexpensive color charts are obtained by **[[wp>Offset printing|offset printing]]**, the color patches are not made from solid color pigments, but obtained using **[[wp>Dither|dithering]]** and **[[wp>Halftone|halftoning]]** of the primary printing colors. The following close-up are taken from the **The 2 in 1** checker, manufactured by **[[https://www.greywhitebalancecolourcard.co.uk/|Grey White Balance Colour Cards]]**; you can see how the patches are obtained with dithering, in particular the second photo shows the **grey patches** on the left: they are made by a **white background with black dots** over it:
  
-{{.:color_management:colorchart-dithering-1.jpg?380|A color chart produced with offset printing}} +[{{.:color_management:colorchart-dithering-1.jpg?380|The GWBCC color chart, produced with offset printing}}] 
-{{.:color_management:colorchart-dithering-2.jpg?380|A color chart produced with offset printing}}+[{{.:color_management:colorchart-dithering-2.jpg?380|The GWBCC color chart; on the left the grey patches}}]
  
 ====== Color calibration using Darktable ====== ====== Color calibration using Darktable ======
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 Here it is an example of what I obtained with the above workflow. The first image is what actually was acquired from the scanner. No particular color space was associated to the image, so if we open the image **assuming the sRGB** color space we get a very dark image (the **histogram** is unbalanced toward the dark tones): Here it is an example of what I obtained with the above workflow. The first image is what actually was acquired from the scanner. No particular color space was associated to the image, so if we open the image **assuming the sRGB** color space we get a very dark image (the **histogram** is unbalanced toward the dark tones):
  
-{{.:color_management:moto-morini-raw.jpg?400|Raw image from the scanner, no specific color space declared, so sRGB was assumed}}+{{.:color_management:moto-morini-raw.jpg?400|Raw image from the scanner}} 
 + 
 +**Raw image from the scanner. If no specific color space is declared, sRGB is assumed (but it is wrong).**
  
 Applying the **linear Rec2020 RGB** color space (just declaring it, without actually changing the pixel data), we get a better image; even the histogram is more balanced between dark and light tones: Applying the **linear Rec2020 RGB** color space (just declaring it, without actually changing the pixel data), we get a better image; even the histogram is more balanced between dark and light tones:
  
-{{.:color_management:moto-morini-colorin.jpg?400|}}+{{.:color_management:moto-morini-colorin.jpg?400|Linear Rec2020 RGB color space applied}} 
 + 
 +**Using Darktable, the Linear Rec2020 RGB color space is applied.**
  
 The final image is just the //raw// one with the **style applied**. A quite good result considering that no manual adjustment was made! The final image is just the //raw// one with the **style applied**. A quite good result considering that no manual adjustment was made!
  
-{{.:color_management:moto-morini-dtstyle.jpg?400|}}+{{.:color_management:moto-morini-dtstyle.jpg?400|Image after applying the Darktable style}}
  
 +**The image after applying the Darktable style.**
 ====== Creating a picture of a color chart ====== ====== Creating a picture of a color chart ======
  
doc/appunti/software/colorchecker_clones.1578808467.txt.gz · Last modified: 2020/01/12 06:54 by niccolo