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Digital-Image Color Spaces, Page 1: Introduction
Article: Table of Contents       Page: 1 · 2 · 3 · 4 · 5 · 6 · 7       This is the first page of a seven-page article

Prolog

There are multiple ways to interpret a number as a speed: “65” in miles/hour is highway cruising speed, but “65” in knots on the highway is a speeding ticket, while “65” in kilometers/hour is only half that speed. “65” in meters/second is a category-4 hurricane, and “65” in Mach is faster than a meteor.

Clearly, when discussing speed, it's important to know not only the raw number, but also the scale in which to interpret it.

Introduction

When it comes to representing color, the digital-image version of this kind of scale is its color space. A digital-image file is made up of raw numeric data — data that is not “color,” but numbers representing color. There are actually many different ways to represent color with numbers in an image file; if an application processing an image file doesn't know which scale was used in creating the image's raw numeric color data (and if it isn't able to guess correctly), it doesn't know how to properly recreate the color when printing or displaying the image. The result is an image with wrong colors, like a TV whose “tint” setting is way out of wack.

Here's an example (me and my son, neither of whom are supposed to be green!):

image whose color space is recognized and understood

Color Data Properly Interpreted

image created with a crazy color space, but without an embedded color pfoile, so it looks wonky

Color Data Misinterpreted

So, a color space is a set of parameters that describe how to convert between numbers and real-world colors. Different color spaces mean different conversions: different real-world colors from the same number, or different numbers from the same real-world color. The technical details are discussed later in the article; for the moment, just consider them abstractly.

File Formats are an Unrelated Topic

To be clear, the concept of a color space is different from a file format. Many image file formats (such as JPEG, TIFF, DNG, etc.) have the ability to use different color spaces — different ways to encode the image color — for their raw numeric data. You can think of a file format as being a standard for how to arrange image data (“such-and-such metadata is allowed, the image is composed of lines of pixels arranged this-and-that way, using such-and-such compression and interleaving....”) and a color space describes how to interpret the per-pixel data into light.

Using music files as an analogy, the “sound space” would be a set of parameters such as the minimum and maximum frequency that can be encoded, the range of amplitudes (volume) that can be encoded, and the mathematical parameters for how the smooth range of encodable real-world frequencies and amplitudes are converted to discrete, raw numeric data.

Color-Space Basics: “sRGB”

The most commonly-used color space is called “sRGB,” which has one overwhelmingly important characteristic: it's the most commonly-used color space. Just about every scanner and digital camera can produce images with sRGB-encoded color. Just about every image-handling device (like printer) and color-aware application (photo editor) can handle images with sRGB-encoded color. In fact, it's the de facto default color space for image input and output of most devices and applications (at least those that understand color spaces). It's the official default color space for the World Wide Web.

The ubiquity of the sRGB color space is really quite convenient.

Because things that produce images (digital cameras, scanners, image-editing software, ....) are on the same color-space wavelength, so to speak, as many things that process or display images (printers, image-viewing software, ...), colors are generally encoded and decoded reasonably well. What you see is not only what you get, but what you're supposed to get.

So, in the face of this overwhelming ubiquity, why would anyone even bother using a different color space for a digital image? (That is, a different method to encode colors with numbers within the raw image data?)

Color-Space Tradeoffs

For technical reasons discussed later in this article, the design of a color space necessarily involves tradeoffs among various aspects of image quality. For example, it might be surprising to learn that it's impossible for a color space to represent all the colors that a human eye can discern, and so some subtle shades must necessarily be omitted (if an image's true color is one of the omitted shades, the encoded color becomes one that's close — usually very, very close — to the true color). So, which shades are included and excluded is one aspect that makes a color space more or less appealing to certain users or artistic tastes.

The next page of this article offers a few more technical details about color spaces and their relative merits, but the main point of this article is merely to introduce the concept of color spaces — ways to convert colors to and from raw numeric data — and why it's important for the photographer to know about them.

Color Profiles

When a different color space is used to encode the raw image data, the resulting data is still just a bunch of raw numbers, so how does a printer or application know that it should consider it in the light of something other than sRGB (or whatever its default color space is)? The answer is usually found in the form of an embedded color profile.

A color profile for a color space is the aforementioned set of parameters that describe the color space, arranged in a standardized way so that they can be communicated along with an image. It can be embedded within a digital image file as metadata, along the same lines as how the date and time are included with the image. This conveniently allows a printer, image-display software, or other color-aware device/application that receives the image file to know the particulars of the color space so that it can properly decode the colors. (If an image doesn't have an embedded color profile, most devices go ahead and decode the colors using the parameters of the sRGB color-space.)

Without the proper color profile associated with the color space used to create the image data, applications don't know how to decode the color data. This results in mixed up or “off” colors, like the “color data misinterpreted” image shown above. That example, by the way, is not a simulation, but an image that looks perfectly normal when interpreted using the proper color space. To ensure that you'd see the wrong colors, I manually removed the embedded color profile from the image file, knowing that your browser would then misinterpret the color data.

Color Profiles Don't Always Get The Respect They Deserve

You might be surprised to find out what happens when I do go ahead and include the proper color profile along with the image, as I do with the middle image here:

image whose color space is recognized and understood
Correct
image with crazy color space, and an embedded color
profile to match
Correct or Wrong?
image created with a crazy color space, but without an embedded color
pfoile, so it looks wonky
Wrong
(For your reference, here is the color profile for the color space used for the center and right-side images.)

Does the middle image look okay or wrong? It depends on how colormetrically-enlightened your browser is:

  • Middle Image Looks Okay: your browser recognizes and respects an image's embedded color profile. Congratulations!

  • Middle Image Looks Wrong: your browser does not recognize or respect an image's embedded color profile. How unsociable!

And herein lies the problem: many browsers are not “color managed” applications, meaning that they do not know how to recognize or understand color profiles.

We'll talk much more about color management later, but first let's look at just how wrong the colors can be in a real-world situation. When creating the sample images shown above, I purposefully used a color space wildly different from sRGB — one that I made up just for this purpose — so that the “wrongness” would be exaggerated and obviously apparent at first glance.

The next page of this article shows a variety of photos encoded with real-world color spaces (color spaces named AdobeRGB, ColorMatch, ProPhoto, WideRGB, and AppleRGB) but without an embedded profile, allowing you to see real-world effects of misinterpreted color.

Continued on the Next Page

This article continues on Page 2: Test Images.


Comments so far....

i got to your article through a link at dpreview forum
article is very clear, thank you. greets from italy
augusto

— comment by augusto on October 22nd, 2006 at 12:53am JST (7 years, 10 months ago) comment permalink

This article is by far the best explanation of these issues I’ve seen on the web. Saves me from having to write one up myself. Thanks!

— comment by Jacob Rus on October 22nd, 2006 at 6:28pm JST (7 years, 10 months ago) comment permalink

Great article Jeffrey, thanks for the clear, detailed explanation… This has actually helped me solve a display problem with a digital camera project I am working on.

— comment by geometrikal on November 20th, 2006 at 11:46am JST (7 years, 9 months ago) comment permalink

Thanks for your great article. I don’t remember ever reading a better one on the subject. Your article is very informative *and* accurate! Many people write so much rubbish about color spaces, and don’t even sense their own misunderstanding of the subject!

— comment by David on January 19th, 2007 at 2:22pm JST (7 years, 7 months ago) comment permalink

This is an excellent read. I’m dealing with multiple browsers and platforms that are calibrated yet I couldn’t get my images to look ‘right’ in non managed applications. I think I’m starting to understand.

Well done!!!

— comment by Scott Watters on February 1st, 2007 at 7:25am JST (7 years, 7 months ago) comment permalink

Examples at
http://regex.info/blog/photo-tech/color-spaces-page2/
are impressive. I didn’t know color spaces are SO different.

A small comment -
“65” in kilometers/hour is only half that speed – a kilometer is a little bit bigger.
Your visitors from Europe can be disappointed.

“Suggestions for Online Image Hosting Services” – I need to ask more questions. What is the best way to do that?

— comment by FP Images on February 21st, 2007 at 9:29am JST (7 years, 6 months ago) comment permalink

Extremely informative article, well reserched and clearly presented. I for one am thankful Jeffery took the time to share his expertise. This explains many of my color space, camera and printing questions.

— comment by Arthur Emerson on February 26th, 2007 at 1:37am JST (7 years, 6 months ago) comment permalink

Thanks,
I was pointed to your article when I was venting about how I couldn’t get my pictures to look good on the web. :) Very helpful!

— comment by Rob on April 10th, 2007 at 10:34pm JST (7 years, 5 months ago) comment permalink

“Without the proper color profile associated with the color space used to create the image data, applications don’t know how to decode the color data.”

I never include a color profile with files I send out for printing. I’ve been advised by the printing service NOT to embed a color profile. The results I get are excellent.

Embedding a color profile is only one way to associate the proper profile with an image. Other methods include notating the color space in the Exif metadata (digital cameras do this), or by mutual agreement as you and your printing service are apparently doing. I would suspect that you’re sending them sRGB and that they’re expecting sRGB. Try converting a copy of an image to, say, ProPhoto and have them print it, and I’m sure you’ll see a huge difference due to the color-space mismatch when you get it printed. —Jeffrey

— comment by Anonymous on June 26th, 2007 at 7:07am JST (7 years, 2 months ago) comment permalink

Excellently written explanation, clarifies a lot of issues -thanks !

FYI you are referenced in this Flickr stream too (though I’m sure the G machine keeps track)
http://www.flickr.com/photos/jurvetson/2049038298

Cheerios
nycandre

— comment by NYC.andre on December 10th, 2007 at 9:48pm JST (6 years, 9 months ago) comment permalink

It’s people like you who make small sections of the net worthwhile and informative when visiting… welcome to my bookmarks!

— comment by Bryant on March 27th, 2008 at 2:59am JST (6 years, 5 months ago) comment permalink

Excellent material — I think I’m finally beginning to understand this stuff. Some related questions:
1) I’ve noticed that Lightroom 2.0 recommends that images are edited in Photoshop with ProPhoto RGB due to its larger gamut. I have my WorkSpace set at AdobeRGB (and I convert to sRGB for saving to Flickr with your excellent plugin – thanks!), and was wondering what the relative pros/cons are about setting my WorkSpace to ProPhotoRGB?

Personally, I leave my workspace set to the native workspace of the image, to avoid color-space conversions. If I want to change it for some specific reason, understanding what happens with the conversion is part of the decision.

2) When your Lightroom 2.0 plugin exports to Flickr, I am assuming that it embeds the requested sRGB profile in the file — is that assumption correct?
and finally,

Images exported from Lightroom have the appropriate profile appended, unless you explicitly strip it with something like my Metadata Wrangler plugin.

3) I have an xRite i1 colorimeter for my LCD monitor. For a while I used to set my Adobe Creative Suite WorkSpace to the i1 generated profile. But I’m now thinking that this is incorrect. I should be setting my WorkSpace to AdobeRGB or ProPhotoRGB, and the colorimeter automatically only affects my monitor profile so that it can correctly interpret the files I am using with Photoshop, Lightroom, etc. Is that right?

That’s correct. A monitor profile is used only for a monitor. sRGB, AdobeRGB, ProPhotoRGB, etc., are device-independent profiles. —Jeffrey

Thanks so much for your excellent writing and work.
Nick

— comment by NickP on August 4th, 2008 at 3:41am JST (6 years ago) comment permalink

Great article. I didn’t realize it was so complicated.

— comment by coloring pages on September 11th, 2008 at 3:15am JST (6 years ago) comment permalink

wonderfull, i feel like a genius because I understand but it is because it was explained so well. Is there a reply to the question posed by NickP? i live in France.

Oops, I let his question slip by… I’ve just gone an added my thoughts. —Jeffrey

— comment by elizabeth on July 1st, 2009 at 5:23pm JST (5 years, 2 months ago) comment permalink

The problem is that Windows browsers are as color-clueless as they come. To my surprise even the new Internet Explore 8 does not recognize imbedded profiles. They simply throw the raw RGB numbers at the screen with no interpretation. Most monitors have a color range that is somewhere in the vicinity of sRGB. There have been several discussions in different forums regarding color management for web images. You can find some comment on http://www.ekdahl.org/kurs/colormanage.htm

— comment by Lars Ekdahl on December 16th, 2009 at 6:56pm JST (4 years, 9 months ago) comment permalink

Fantastic explanation, thank you. Maybe you can help me with a problem I am having. My HTML website displays sRGB images correctly on my calibrated wide gamut monitor. This I believe is because the ICC profile is embedded in the image telling Safari to display it in sRGB. But, with flash the ICC profile doesn’t seem to be attached to the image and so Safari doesn’t know what to do and tries to display it with it’s default setting ~ the monitors ICC profile. In this case on my wide gamut monitor which has a much larger colour space resulting in the image in Safari looking overly saturated in red.

Do you know a way around this?

I read saving your images in your calibrated monitors profile is a work around?

Does Flash CS5 embed ICC profile now? Would that resolve this?

Last I heard Flash has no color management. Saving images with your monitor’s profile square-pegged as a device-independent profile will work perfectly for everyone on earth that’s exactly you, but no one else. Only way I know of to get a color-managed browser to match up images in HTML and Flash are to strip all color profiles from the images, because Flash treats them that way, and so the result ends up being random, but equally random for all situations. —Jeffrey

— comment by Justin on October 8th, 2010 at 4:20pm JST (3 years, 11 months ago) comment permalink

Yes, I thought that might be the case with applying the monitors profile. And I’ve seen posts on various forums advising to strip all colour profiles.

I ask as I would like to replace my HTML site with a new Flash site. Is there is no way to get the same colour accuracy with Flash as with HTML? I just seems so crazy?

Last I paid attention (a few years ago), Flash was not colormanged, so that’s just one more in a long list of reasons why Flash is not appropriate for internet web sites. (Intranet sites, where one entity controls all content consumers, is quite a different beast). I own stock in Adobe so it’d be great for my pocketbook if everyone flocked to Flash, but as a user I despise it on Internet sites. —Jeffrey

— comment by Justin on October 8th, 2010 at 4:40pm JST (3 years, 11 months ago) comment permalink

Much appreciated Jeffrey, curiously billy-kidd.com flash website doesn’t have this colour problem? I do not believe it is an intranet site. Having gone through forums for the last two days, torture BTW, the only thing I can find is that CS5 states it can now embed IIC profiles. However, it doesn’t explain what this feature is and whether this will resolve this issue. If I find out I will let you know!

Thank you
Justin

— comment by Justin on October 9th, 2010 at 1:53am JST (3 years, 11 months ago) comment permalink

This is brilliant. Thank you so much. I have had a huge headache over color management that is slowly abating as I read this wonderful series of articles. Bless you.

Amanda in SoCal

— comment by Amanda on November 3rd, 2010 at 2:30pm JST (3 years, 10 months ago) comment permalink

Answers. Flash sites can be coded to display sRGB ICC profile correctly on colour managed browsers such as safari without effecting browsers such as internet explorer which do not colour manage.

You need flash site built with actionscript 3 for flash player 10. Then add following to beginning of site and it will correct colour managed browsers, even on wide gamut monitors:

“if (stage.colorCorrectionSupport == ColorCorrectionSupport.DEFAULT_ON || stage.colorCorrectionSupport == ColorCorrectionSupport.DEFAULT_OFF) stage.colorCorrection = ColorCorrection.ON;”

Explained in more detail here:
http://www.adobe.com/devnet/flash/quickstart/color_correction_as3.html

Hope this helps!

— comment by Justin on December 8th, 2010 at 5:16pm JST (3 years, 9 months ago) comment permalink

the link to the icc color profile is broken

Yikes, not sure how that happened. Thanks for the heads up. Fixed. —Jeffrey

— comment by biaib on June 23rd, 2011 at 12:09am JST (3 years, 2 months ago) comment permalink

Hi! I just discover your blog through your “exif viewer” page and I just realise that I may have some color profile problems in my workflow… The software that I use to convert my tiff files to jpg does not keep image color profile in the final file, and the most strange is that even when I convert directly a raw file in jpg with Canon DPP (with the “include icc profile” box checked) , exif viewer tells me :
“WARNING: Embedded color profile: “Z009”
Some popular web browsers ignore embedded color profiles, meaning users of those browsers will see the wrong colors for this image.
STRANGE: The embedded color profile differs from the metadata tags (sRGB (EXIF:ColorSpace)).”
notice that sRGB is really the profile configured in my camera settings and DPP default settings…

How can I understand that?

Thanks for your very interesting blog and beautiful photos!

— comment by brunauto on February 5th, 2012 at 9:25pm JST (2 years, 7 months ago) comment permalink

Oh, I didn’t saw that the ICC profile is at the bottom of the page and must be extended to be seen.
Actually on a photo directly edited in jpg by DPP, it is written that Z009 is the device model (?) and near the the bottom of the block there is “Profile Description” > sRGB v1.31 (Canon).
But at the top of this block, above the data, it is written “A profile by Canon that claims to be an sRGB color profile, but is actually slightly different.”
It is less clear to me… :-\

I don’t recall what was different about it (and silly of me for not keeping track of it), but it’s likely something not particularly important. Try comparing it with a different sRGB profile to see what’s different, I guess. —Jeffrey

— comment by brunauto on February 6th, 2012 at 4:40am JST (2 years, 7 months ago) comment permalink

Hi, would it be that we have to set our DSLR camera at sRGB and NOT Adobe

It’s best to set it to raw. —Jeffrey

— comment by victor on March 24th, 2012 at 12:10am JST (2 years, 5 months ago) comment permalink

Further to your response, the reason for my query is that the printer that Zenfolio use requires that anything sent to them has a set profile in order to get the very best out of the images. If I get the stuff as good as I can on a colour corrected screen, apply the profile then upload it, the printer should produce an image for my clients that matches my screen.

I know that clients looking at the image will get see a result which is not perfect, but for most it will be good enough – I have looked at the images pre and post profile and although there is a difference, it is minor, thus my thoughts

Okay, I see, it may be that my initial response was ignorant, sorry. If Zenfolio passes your original uploads directly to the printer as is (while still converting to sRGB for web display) and the printer actually pays attention to the color space, that would be exceptionally clueful. I host my images on my own blog so haven’t paid close attention to these details at Zenfolio, but if you install the color profile from the printer to your system and restart Lightroom, the profile should appear in the “File Settings” section of the export dialog. Selecting it may trigger a warning in the “Zenfolio: Upload Destination” about a non-sRGB color space, but if so just go there to override it because you clearly understand what’s going on. —Jeffrey

— comment by Laurence J. Power on September 9th, 2012 at 5:36pm JST (2 years ago) comment permalink

Thank you for this article, the beautiful photos and the helpful plug-ins.

You and/or others may also be interested in this page:

RGB-to-XYZ and XYZ-to-RGB matrices http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html#WSMatrices
http://www.brucelindbloom.com/index.html

and this article which provides a 3D visualisation as well as a method to create it:
http://www.photo-mark.com/notes/2013/mar/13/color-theory-blender/

— comment by Pamela on March 24th, 2013 at 10:10am JST (1 year, 5 months ago) comment permalink

Hi, great app.

When I add a file and I hit view image from file I get the following:

Under ICC_Profile — this block of data describes the color space used to encode pixel colors

In that information it lists the profile date time. What does that date time mean? Is it the actual time the image was taken?

Writing from Cheney Washington home of Eastern Washington University.

Thanks,

Brian

No, it’s the date/time the profile was made, which is not very useful for much. It’s like a notation in a book describing when the ink was made. —Jeffrey

— comment by Anonymous on April 13th, 2014 at 4:50pm JST (4 months, 19 days ago) comment permalink
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