Introducing Wide Gamut Wednesdays

This week I’m kicking off a new series of posts that set out to answer a simple question:

“Can an HDTV accurately reproduce these colors?”

I’m calling the new weekly feature “Wide Color Gamut Wednesday” or #WideColorWednesday in social media speak. Each week we will analyze a new wide color gamut image and post the results to our @dot_color Twitter feed.

In the process, I think we’ll find that “wide gamut” colors – colors that fall outside the BT.709 color gamut used by HDTVs – are actually fairly common beyond classic examples like Brazilian tree frogs or Coca Cola cans. In fact, in our first test, we found a simple image of spring flowers, taken in Rochester, NY, contained mostly colors that fall outside the BT.709 gamut.

Wide Color Gamut image analysis

62.5% of the colors in this springtime flowers image fall outside the BT.709 color gamut used by HDTVs #WideGamutWednesday

I thought it would be helpful to write up the first #WideColorWednesday image as a blog post with some background on the process used to create these images.

Source Image

Since it’s springtime here in Northern California I chose a vibrant photo of spring flowers for our first image. It’s also a great example of a commonplace scene that benefits from wide color gamut colorimetry.

Image credit: Michelle Yeager via 500px.com license, captured in ProPhotoRGB color space by a Nikon D7000 DSLR camera.

The slider above highlights out-of-gamut BT.709 colors in grey. It’s easy to see here that most of this image falls outside the range of colors that a BT.709 display can accurately reproduce.

Analysis & Results

ProPhoto RGB vs BT.2020 Color Space.001

This image was captured in the massive ProPhoto RGB color space originally developed by Kodak in the late 1990’s for use in professional photography. ProPhoto’s primaries were optimized to capture a huge range of colors including 100% of Pointer’s gamut colors while reducing hue shifts in processing (hence the somewhat unusual placement of two of its primaries outside the CIE locus). ProPhoto also covers over 100% of BT.2020 and BT.709 color gamuts so this photo should contain plenty of data for our analysis.

The image was first cropped to fit our infographic template and converted to the BT.2020 color space using Photoshop. I then analyzed the data in the converted image using Matlab to generate a CIE 1931 plot of the xy coordinates of each pixel in the image. The color of these data points matches the color of the corresponding pixel in the original image so it’s easy to see what part of the image it came from.

Wide Color Gamut Analysis Spring Flowers

Color gamut analysis of spring flowers test image showing the chromaticity of each pixel in the image plotted as CIE 1931 xy coordinates.

The result shows that 62.5% of the colors in this image fall outside the BT.709 color gamut. This means a typical HDTV can accurately reproduce just 37.5% of the pixels in this image.

Stay tuned…

Going forward, these #WideColorWendesday images will only appear on the @dot_color Twitter feed to avoid spamming subscriber inboxes every week. Please follow-along there if you’d like to see the how these turn out. In the meantime, if you have an image that you’d like to have analyzed – and don’t mind sharing it with this audience – please let me know in the comments.

Special thanks to Ernie Lee for the MatLab expertise!

2 thoughts on “Introducing Wide Gamut Wednesdays

  1. Hi Jeff,
    Thank you for starting this series on wide gamut imagery. I am looking forward to these posts.

    I am doing research on gamut mapping, developing both gamut reduction and gamut extension algorithms. Getting good images with many out-of-BT709 colors is difficult, which is why it would be great if you could please share with us these wide-gamut images (that we can download).

    Thank you.

    regards,
    Shah

    • Hi Shah, it’s great to hear about the work you are doing on wide color gamut imagery! I cannot share our images with you due to copyright restrictions. However, I recommend you take a look at 500px.com. This website allows you to search for images based on color profile. You can find a huge number of wide gamut-encoded images available for licensing there. This blog post is a good overview of the functionality and may help you get started: https://iso.500px.com/500px-color-profiles-file-formats-and-you/

      -Jeff

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