Color Spaces, Part 4: Lab

THE MOST COMMON models of human color vision take three precisely-determined shades of red, green, and blue light, and mix them together in various proportions to generate a gamut of colors. The familiar sRGB standard, proposed by Microsoft and Hewlett-Packard in 1996, is supported by most computers, digital cameras, scanners, projectors, and printers as the standard color model, and sRGB is the color model assumed by the world wide web and most common image file formats.

RGB color models are very useful. A computer monitor typically has a large array of tiny red, green, and blue colored cells, these cells being so small that we cannot see them without a magnifying glass. The cells blend together to give us the other colors. For example, if the red and green cells are turned on, and blue is turned off, we are likely to get a shade of yellow. This physical process of mixing colors of light is very similar to how colors are defined in the various RGB color models: the primary red color in sRGB is defined as the three color numbers [255, 0, 0] and the computer monitor will likewise fully turn on the red cells while keeping the green and blue cells off. A particular medium gray color, defined in sRGB as [186,186,186] will cause the computer monitor to set the red, green, and blue cells to an intermediate value about halfway between fully on and fully off. Now, while no computer monitor or other digital imaging device has precisely the same properties of the sRGB standard, these are usually designed to be close enough for most purposes.

But there are some problems. First, you cannot mix red, green, and blue paint together to do decent painting, for we aren't mixing pure light, like on a computer screen, but rather are mixing together pigments which absorb some of the light falling on them, reflecting away the rest. And so, the RGB color system isn't particularly useful for painters, and is likely highly misleading: see the article Additive versus Subtractive Color. Furthermore, you cannot get all shades of colors by mixing together only three colors of lights.

The image below, called a CIE chromaticity diagram, shows the range of saturated colors that can be seen by the human eye:



[source]

The curved outline shows the full gamut of human vision, while the triangle within it shows the gamut of the sRGB color standard. If you use three primary colors for your standard, your available colors will be limited to only those colors within the triangle. sRGB excludes pure spectral violet, and deep scarlet red, and also neglects bright cyans and greens. Please note that this image itself is fully within the sRGB color standard, and so we cannot show you here the full range of visible colors, only the relative amount of color that can be represented by sRGB.

Staying Hip is a Full-Time Job

SEEN ON REDDIT:

A:  Sometimes I feel like there are no contemporary art movements left but "Postmodernism."

B:  Didn’t you get the memo? Postmodernism is over and done with. Don't ask where we are now.

A:  does that mean painting is cool again?

B:  Now it gets confusing. Post rock means you can use accoustic gitars again, and hispsters play vinyl records and use analogue cameras. Ergo: Post-Hip Post-modernism means you can paint again.

Blue Cameras Take the Best Pictures

Click the link for something funny:  Ah, Managers

Composition, Part 1 - the Frame

I MUST ADMIT that the technical aspects of photography are easiest for me. Color spaces, exposure and lens calculations, f/stops, shutter speeds, and ISO sensitivity are generally objectively certain and quantifiable. On the contrary, artistic considerations such as the use of color itself and composition seem to be subjective, qualitative, and much less certain. However, we must not oppose technique with art: they are not two things, but are different aspects of one thing, and they both must be taken into consideration when making a final image.

When I became serious about photography a number of years ago, I didn't give composition too much consideration, simply due to the fact that I was taking mainly architectural photos:



Saint Francis Xavier Church, at Saint Louis University, in Saint Louis, Missouri, USA.

The hard work of composition was already done for me by the architect. I merely had to discover good camera positions and angles, and the kind of post processing that would express the work of the architect in a pleasing manner. Fortunately, these discoveries came rather quickly to me.

Likewise, I found it easy to take pleasing photos of flowers:



Flower, at the Missouri Botanical Garden (Shaw's Garden), in Saint Louis.

Flowers are intrinsically interesting, and nature suggests composition.

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Photoshop Wishlist #2

1. When I apply noise reduction in Photoshop — no matter what technique I use — the apparent saturation decreases. Why is this? How can this be avoided? I don’t want to merely add saturation back in, but avoid it. I’ve noticed the same thing with small-sensor digital cameras, those that do lots of noise reduction in-camera.
2. Are there any good techniques to get rid of the brightly colored noise found along edges? This is due to demosaicing the Bayer array of the sensor. Eliminating this noise usually leads to desaturation of the good pixels.
3. Photoshop does not resize images well, and often generates interference patterns. Lots of research has been done on these kinds of algorithms, and it would be good to see these better solutions in Photoshop. Also, fractal resizing has many benefits and would be valuable to have also.
4. I’d like to be able to fully edit ICC profiles in Photoshop. For example, I have a profile that uses the GRACoL ink colors, but has other parameters I’d like to change. The Custom CMYK interface is rather lacking.
5. When you use curves in RGB, you can either do it with the Normal blending mode, which typically causes an increase in saturation, or you can do it with Luminosity blending, which decreases saturation. How about a simple method which does neither? I just want the tonality to change, not the basic coloration. Click here to see how it is done.
6. A solid method of adding local contrast. ‘HDR toning’ does this a bit, and a lot of other things at the same time too, making it less useful. ‘Clarity’ is pretty good, but tends to produce halos also. There are better methods.
7. A ‘Vibrance’ tool for CMYK. This increases saturation without causing any channel to blow or plug.
8. I’ve noticed that there is a distinction between chroma, colorfulness, and saturation; not really sure how or what Photoshop does. A solid colorimetric model would be useful.
9. More color spaces. XYZ and xyY would be useful.
10. Using Munsell colors in the color picker would be great, as well as better out-of-gamut warnings.
11. Better statistical color tools. Something that can show all the colors in an image as a three-dimensional solid would be great.

Yeah, I know. All of this development is expensive, and it is easy to criticize!

Using ICC Profiles for Creative Color Control

Notice: the ICC profiles I link to in this article are now accessible again.



COLOR MANAGEMENT has become far easier since the introduction of standard ICC profiles, developed by the International Color Consortium, a group of various computer, digital camera, and imaging companies. ICC profiles describe the color handing characteristics of cameras, scanners, printers, and computer monitors, as well as allowing for uniform methods of converting the colors from one device to another. For example, ICC profiles are used to convert the colors captured by a camera to those colors available on a printer.

ICC profiles define a mapping from the typically limited color spaces of devices into a universal color space (which can describe all colors), such as CIELAB or CIEXYZ; from these universal spaces, the colors can then be mapped to an output device. As such, ICC profiles recognize limits of what is possible with any given device, and allows us to compare the capabilities of one device with another. If an output device, like a computer display or digital printer, cannot show particular colors, then the software will use the ICC profile to change the colors to the closest ones available (this will often cause the image to lose detail or saturation).

ICC profiles are also stored in image files, thereby interpreting the colors of the file, and these profiles are used during image editing. Typically, JPEG image files delivered by cameras are encoded into standard color spaces which are independent of the particular make and model of camera. The most common color spaces are sRGB and AdobeRGB; these provide a wide enough gamut of color for practical use, while being compact enough to produce reasonably small file sizes. ICC calls these "three component color encoding" standards. Using these standards are convenient because we can use JPEG or TIFF images from a wide variety of cameras without worrying about the specific characteristics of each. For example, an sRGB color value of (255, 0, 0) will describe the same bright red color, no matter where the image came from.  Some software, including web browsers, actually assume that all image files are encoded in the sRGB standard.

Click here for an overview of RGB color spaces.


I did not create this image. Click here for source and attribution. This shows the relative color gamuts of various RGB color profiles, as well as the color gamut of the Epson 2200 printer.

Each of the standard RGB ICC profiles defines three primary colors: particular shades of red, green, and blue. A narrow standard such as sRGB can describe about 35% of all colors, and so will have primary colors that aren't quite as bright, colorful, or saturated as the Wide Gamut RGB standard, which can describe about 77.6% of all colors. The ProPhoto standard is even bigger and has mathematical primaries that aren't even real colors.  However, be aware that most computer monitors and digital printers cannot display or print color much beyond the sRGB standard, and so sRGB is generally recommended for most uses on the Internet and for consumer-grade printing.

So ICC profiles have these uses:

• Describing the color capability of a device.
• A standard method of converting the colors from one device to another.
• Describing the colors in an image file such as a digital photograph.
• A widely accepted color standard for cross-platform image interchange.

May I also propose another use of ICC profiles?

• Creative use. Artists can use ICC profiles to precisely manipulate and control the gamut of color in images.

In his book Professional Photoshop (5th Edition), Dan Margulis described the use of 'false profiles': using ICC profiles as an alternative method of image manipulation. He used this method to greatly brighten shadow detail without modifying the color: this is difficult to do with the standard Photoshop tools.

"photographs very rarely turn out good likenesses"

The first thing that caught my attention was a portrait of mother that hung over the writing table; a photograph in a magnificent carved frame of rare wood, obviously taken abroad and judging from its size a very expensive one. I had never heard of this portrait and knew nothing of it before, and what struck me most of all was the likeness which was remarkable in a photograph, the spiritual truth of it, so to say ; in fact it looked more like a real portrait by the hand of an artist than a mere mechanical print. When I went in I could not help stopping before it at once.

"Isn't it, isn't it?" Versilov repeated behind me, meaning, "Isn't it like?" I glanced at him and was struck by the expression of his face. He was rather pale, but there was a glowing and intense look in his eyes which seemed shining with happiness and strength. I had never seen such an expression on his face.

"I did not know that you loved mother so much !" I blurted out, suddenly delighted.

He smiled blissfully, though in his smile there was a suggestion of something like a martyr's anguish, or rather something humane and lofty ... I don't know how to express it; but highly developed people, I fancy, can never have triumphantly and complacently happy faces. He did not answer, but taking the portrait from the rings with both hands brought it close to him, kissed it, and gently hung it back on the wall.

"Observe," he said; "photographs very rarely turn out good likenesses, and that one can easily understand: the originals, that is all of us, are very rarely like ourselves. Only on rare occasions does a man's face express his leading quality, his most characteristic thought. The artist studies the face and divines its characteristic meaning, though at the actual moment when he's painting, it may not be in the face at all. Photography takes a man as he is, and it is extremely possible that at moments Napoleon would have turned out stupid, and Bismarck tender. Here, in this portrait, by good luck the sun caught Sonia in her characteristic moment of modest gentle love and rather wild shrinking chastity….

—from A Raw Youth, by Fyodor Dostoevsky (1821-1881), translated by Constance Garnett