HAS A PHOTO been severely altered? I’m sure you’ve seen examples of photo forgery lately in the news media. How exactly can you detect if a photograph is a composite of more than one original camera image? How can you tell if the clone tool has been used on an image, replacing scene detail at one part from another?
See the Digital Forensics webpage for original research by Hany Farid and his group at Dartmouth College.
Of particular interest is a large PDF file of lecture notes, which starts out with a number of famed doctored photographs from history, and then immediately jumps into complex mathematical examinations of digital images.
Saturday, May 12, 2012
Tuesday, May 8, 2012
Ars Photographica
Ars PhotographicaThis poem was set to music by Gavin Bryars, and is available on Amazon: On Photography - Bryars, Maskats, Silvestrov
Vincenzo Gioacchino Raffaele Luigi Cardinal Pecci
1867
Expressa solis spiculo
Nitens imago, quam bene
Frontis decus, vim luminum
Refers, et oris gratiam.
O mira virtus ingeni
Novumque monstrum! Imaginem
Naturae Apelles aemulus
Non pulchriorem pingeret.
On Photography
(translated by H.T. Henry, 1902)
Sun-wrought with magic of the skies
The image fair before me lies:
Deep-vaulted brain and sparkling eyes
And lip's fine chiselling.
O miracle of human thought,
O art with newest marvels fraught -
Apelles, Nature's rival, wrought
No fairer imaging!
.
Saturday, April 21, 2012
“St. Louis Parks”
ST. LOUIS PARKS — a new book from Reedy Press — with photography by yours truly, including the photo on the cover:
This view shows the World’s Fair Pavilion atop Government Hill, in Forest Park, in the City of Saint Louis, Missouri. Teenagers are seen here enjoying the cool water of the fountain on a warm June day. I think this photo adequately captures the joy and simple pleasure that ought to be found in a pleasant park.
This book contains over a hundred of my photos of parks located within the City of Saint Louis. Click here to get your own copy of this book:
From the publisher, Reedy Press:
St. Louis Parks By NiNi Harris and Esley Hamilton, Foreword by Peter H. Raven
St. Louis has great parks. And St. Louisans are passionate about them. St. Louis Parks delivers portraits of St. Louis City and County parks, both major and minor, that prove why these common spaces are crucial to the region’s way of life.
Acclaimed local historians NiNi Harris and Esley Hamilton take readers through the city and county, respectively. Starting with the establishment of Lafayette Park from thirty acres of common fields in 1836, Harris covers the creation of gems like Tower Grove Park, the nation’s finest Victorian Park, and the dazzling, 1,293-acre Forest Park, while including Citygarden, and its interactive artwork, in the heart of downtown.
In the county, Hamilton highlights one-of-a-kind attractions like the renowned Museum of Transportation and Laumeier Sculpture Park, the Butterfly House and St. Louis Carousel at Faust Park, a farm zoo at Suson Park, and the military museums at Jefferson Barracks. In both sections, the authors recognize the citizens, civic leaders, and architects whose work delivered to all St. Louisans picturesque landscapes, ball fields, tennis courts, natural savannahs, and grasslands filled with wildlife, and trails that lead runners through forests and by shimmering lakes.
Dramatic photography by Mark Scott Abeln and Steve Tiemann complement the essays. The photographs evoke the unique character and history of the individual parks. They visualize the importance of green space for both escaping and coming together as a community.
ABOUT THE AUTHORS AND PHOTOGRAPHERS
NiNi Harris’s earliest memory is of an early autumn evening, picking up acorns as she and her father walked along Bellerive Boulevard to Bellerive Park. Her great- great-grandfather’s first job when he arrived in St. Louis in 1864 was planting trees in a St. Louis park. This is her tenth book on St. Louis history and architecture.Mr. Peter Raven is President Emeritus of the famed Missouri Botanical Garden.
Esley Hamilton has been working for the St. Louis County Department of Parks and Recreation as historian and preservationist since 1977. Among preservation-
ists in the St. Louis region, Hamilton’s is a household name. He teaches the history of landscape architecture at Washington University and serves on the board of the National Association for Olmsted Parks.
Mark Abeln is a native of St. Louis and attended college at Caltech, in Pasadena, California. Mark started taking photography seriously after he took disappointing photos of an important subject. He spent the next years learning the art of photography, and his photos can now be found in numerous publications as well as on his website “Rome of the West.”
Steve Tiemann graduated from McCluer High School and went on to obtain his forestry degree from the University of Missouri at Columbia. Steve has enjoyed his career as a park ranger and park ranger supervisor with St. Louis County Parks for nearly thirty years. He tries to be in ready mode with a camera while patrolling on foot or bike.
This book’s publication date is May 1st. You can order a copy now:
You can also purchase my earlier book of photography, Catholic St. Louis: A Pictorial History:
Tuesday, April 10, 2012
A Good Photograph
SOMEONE ASKS, “What makes a good photo?”
According to modern philosophies, if any answer to this question is given at all, it is usually convoluted, unsatisfactory, or it has nothing to do about photography. Instead, I will go back to ideas discovered by the philosophers of Greece and the Middle Ages, eras that produced great art that astonishes us still.
A good photograph will please the eye and give it rest. Nothing can be seen that ought to be removed, nor can the imagination perceive anything that ought to be added or changed.
A good photograph will cause the viewer to stand outside of himself for a brief moment. The viewer, in his imagination, is transported within the frame of the image.
A good photograph will reward a viewer every time he sees it. He can contemplate it many times for many years, and yet discover new things never before noticed. It does not grow stale or boring over time.
A good photograph will evoke immediate recognition within the viewer. The viewer will think that he has seen the photograph before; indeed, the photograph will seem to be a part of the viewer’s earliest memories.
A good photograph will become a part of the viewer. The viewer will use his memory of the photograph as a type and model for other things.
A good photograph will cause the viewer to see that this particular photograph is the most appropriate medium for expressing the subject.
A good photograph will have a sense of unity — each part will relate in some way to every other part.
A good photograph will have due proportion and symmetry, a formal structure that is harmonious and expressive of the subject matter.
A good photograph will have a clarity and vividness that expresses the photographer’s intention.
A good photograph will clearly show the truth, even if what is depicted is not factually true, but rather instead expresses a higher truth.
A good photograph will obviously show that the photographer has mastery over the medium.
A good photograph will elicit a lively positive response from all who view it, without regard to age, sex, race, nationality, education, class, party, or religion.
Now, this is a very high target to aim for, and very few photographs ever come close. But it helps to know what we are aiming for, even it we always shoot low. These ideas are also applicable to very many of the fine arts, and not just photography.
According to modern philosophies, if any answer to this question is given at all, it is usually convoluted, unsatisfactory, or it has nothing to do about photography. Instead, I will go back to ideas discovered by the philosophers of Greece and the Middle Ages, eras that produced great art that astonishes us still.
A good photograph will please the eye and give it rest. Nothing can be seen that ought to be removed, nor can the imagination perceive anything that ought to be added or changed.
A good photograph will cause the viewer to stand outside of himself for a brief moment. The viewer, in his imagination, is transported within the frame of the image.
A good photograph will reward a viewer every time he sees it. He can contemplate it many times for many years, and yet discover new things never before noticed. It does not grow stale or boring over time.
A good photograph will evoke immediate recognition within the viewer. The viewer will think that he has seen the photograph before; indeed, the photograph will seem to be a part of the viewer’s earliest memories.
A good photograph will become a part of the viewer. The viewer will use his memory of the photograph as a type and model for other things.
A good photograph will cause the viewer to see that this particular photograph is the most appropriate medium for expressing the subject.
A good photograph will have a sense of unity — each part will relate in some way to every other part.
A good photograph will have due proportion and symmetry, a formal structure that is harmonious and expressive of the subject matter.
A good photograph will have a clarity and vividness that expresses the photographer’s intention.
A good photograph will clearly show the truth, even if what is depicted is not factually true, but rather instead expresses a higher truth.
A good photograph will obviously show that the photographer has mastery over the medium.
A good photograph will elicit a lively positive response from all who view it, without regard to age, sex, race, nationality, education, class, party, or religion.
Now, this is a very high target to aim for, and very few photographs ever come close. But it helps to know what we are aiming for, even it we always shoot low. These ideas are also applicable to very many of the fine arts, and not just photography.
Tuesday, March 27, 2012
Nothing to do About Photography...
...BUT PERHAPS AN inspiration to those seriously interested in the art of photography. Take a look at The Textile Blog: Design, Decoration and Craft.
Textiles and photographs are both flat, basically two-dimensional art forms. Both are typically made by machines and are usually not hand-made, although there is much artistry in both mediums. Certainly there is something for a photographer to learn about composition and art from examining other, similar art forms.
We live in an age of increased specialization, rationalization of labor, narrow job categories, hair-splitting definitions of genres, and narrow disciplines that do not understand each other. Now, some can call this individuality, but this division perversely leads to centralization, excess standardization, and the sense that we are seen as easily-replacable cogs in a huge machine, and not as free men and women.
For this reason, I think that a good education in the liberal arts is important if you want to improve your art, as well as avoiding too much specialization in art. The Textile Blog seems to understand this, and features artists who were much more and broader in scope in their artwork than what we tend see these days.
Textiles and photographs are both flat, basically two-dimensional art forms. Both are typically made by machines and are usually not hand-made, although there is much artistry in both mediums. Certainly there is something for a photographer to learn about composition and art from examining other, similar art forms.
We live in an age of increased specialization, rationalization of labor, narrow job categories, hair-splitting definitions of genres, and narrow disciplines that do not understand each other. Now, some can call this individuality, but this division perversely leads to centralization, excess standardization, and the sense that we are seen as easily-replacable cogs in a huge machine, and not as free men and women.
For this reason, I think that a good education in the liberal arts is important if you want to improve your art, as well as avoiding too much specialization in art. The Textile Blog seems to understand this, and features artists who were much more and broader in scope in their artwork than what we tend see these days.
Thursday, March 15, 2012
An Imitation of the Autochrome Lumière Process
THE EARLIEST PRACTICAL method of color photography was the Autochrome Lumière process, introduced in France in 1907 by the Lumière brothers, who earlier had invented cinematography. Autochrome used standard silver chemistry, but with specially prepared glass plates, coated with tiny grains of transparent starch, dyed to three primary colors. This process produced slides suitable for projection or for viewing with bright back lighting; the colors produced were rather dark and somewhat muted, but many consider the final results to be rather beautiful. Later color photography methods tended to produce colors that could be garish.
Family group outdoors, by unknown, ca. 1915, George Eastman House Collection
Woman posed as sphinx, by Dr. W. Simon, ca. 1910, George Eastman House Collection
Woman in floral silk robe, by Charles Spaeth, ca. 1915, George Eastman House Collection
Intrigued by this process, and captivated by many of the historical Autochrome images found on the Internet, I attempted to recreate the ‘look’ of these images. Since Autochrome is an additive process, using light-transmitting filters, the color properties of Autochrome ought to be quite reproducible with contemporary computer software.
The main problem is discovering the three primary colors used, and by various methods I was able to come up with a color gamut which seems to be fairly close to the original Autochrome. Characteristically, the primaries seem to be reddish-orange, a weak blueish violet color, and green. Using these primary colors, I was able to easily convert digital images to use this supposed Autochrome gamut:
This process, with its narrow gamut of colors, lacks the ability to capture reds and saturated blues, but it produces nice shades of pink and violet, as well as prominent orange and pale cyan colors. You can see other attempts at Autochroming images in my article Autochrome here and Autochrome at my other blog.
My process uses custom ICC profiles, created in Photoshop, which are linked in my article Using ICC Profiles for Creative Color Control. If you download one of these profiles, you can use standard image editing software to convert your standard profile images to use my estimates of the Autochrome primary colors. The nice feature of this method is that once you convert an image to use the Autochrome profile, you can edit the image as much as you would like while never having the colors go out of gamut. Once you are finished editing, you convert the image back to the standard sRGB profile for viewing on your computer or for printing.
While this is satisfying and interesting, these images lack prominent characteristics of the original Autochrome process, namely, the dark “gamma” of the images as well as the pointillistic grain pattern which derives from the colored starch grains found on Autochrome plates. Certainly my work with the Autochrome color gamut is sufficient to produce interesting images with a limited range of colors reminiscent of Autochrome, but I think it would be interesting, and possibly valuable, to come up with a better digital imitation of the historical method.
I don’t claim that my Autochrome color profiles actually match the color gamut found in the original process, for the sample images found on the Internet are highly variable, but with common characteristics. But close is good enough. Likewise, if I attempt to imitate the pointillistic nature of Autochrome, then close will again be good enough. It is my intention to create a method that is adequate.
In the article What is Autochrome? at the website of the Šechtl & Voseček Museum of Photography, you can see a microphotograph of the starch grains found in Autochrome, as well as many sample images and a description of the process.
The grains are generally round, bunched together in clusters, with a small amount of black pigment between the gaps. This grain, somehow, needs to be reproduced in Photoshop for our process. Now producing a photorealistic imitation of these grains would be very difficult, impractical, and would tax the resources of my computer, so I will produce a pixelated version instead, with clumps of square instead of round grains.
I’ve read a number of estimates of the sizes of the starch grains, from 5 to 10 microns in size, and some say that the process used 4 million grains per square inch. For our purposes, knowing the number of grains per linear inch is important, and various authorities state 1700, 2000, and 2500 grains per linear inch.
The Autochrome plates were manufactured in a wide variety of English and metric sizes. The pointillistic ‘look’ of the images is quite prominent on smaller plate sizes, but is not particularly noticeable on digital images made from larger plates. For our purposes, we’ll imitate the characteristics of a small plate, 3-1/4x4 inches in size, and use the intermediate value of 2000 grains per linear inch, which gives us an image 8000 x 6500 grains in size, or a 52 megagrain image. Please note that the color grains in Autochrome are randomly scattered, and so there is significant clumping of colors, reducing the final resolution and color accuracy of the image. Because it does not have the regular pattern of the Bayer sensor found in most digital cameras, Autochrome does not illustrate aliasing or the Moiré effect.
Now I have no idea as to the size of the light-sensitive silver grains found in Autochrome, but I’d think that the silver grains were smaller than the color grains, otherwise there would be a significant loss of saturation. I’m not sure how much this matters, but from my experimentation, very many color grains improve the final results. My digital camera is rather aged, and produces images 3008 x 2000 pixels in size, and using a grain pattern that size produces images that have an objectionable amount of grain. If we have a target of 6500 grains along the short edge of my image, then I will upsize from 3008 x 2000 to 9776 x 6500, preserving the aspect ratio, while imitating the grain pattern found in the smaller sample images. This would be roughly equal to an Autochrome plate 3-1/4 x 4-7/8 inches in size.
The difficult part of this process is creating a pixelated version of the color grain pattern of Autochrome, and it needs to be made in exactly the same number of pixels as the upsized image. As each manufacturer makes slightly different aspect ratios of images — and even some RAW converters will vary the number of pixels, then you will have to make your own grain pattern.
This is a highly-zoomed portion of a grain pattern that I made. Each pixel substitutes for an Autochrome grain, and like the original Autochrome, the grains are clumped together instead of being uniform. It doesn’t matter that it uses the standard sRGB primary colors, and not those of Autochrome.
Here is how I made it in Photoshop CS5:
Before:
After:
Before:
After:
Family group outdoors, by unknown, ca. 1915, George Eastman House Collection
Woman posed as sphinx, by Dr. W. Simon, ca. 1910, George Eastman House Collection
Woman in floral silk robe, by Charles Spaeth, ca. 1915, George Eastman House Collection
Intrigued by this process, and captivated by many of the historical Autochrome images found on the Internet, I attempted to recreate the ‘look’ of these images. Since Autochrome is an additive process, using light-transmitting filters, the color properties of Autochrome ought to be quite reproducible with contemporary computer software.
The main problem is discovering the three primary colors used, and by various methods I was able to come up with a color gamut which seems to be fairly close to the original Autochrome. Characteristically, the primaries seem to be reddish-orange, a weak blueish violet color, and green. Using these primary colors, I was able to easily convert digital images to use this supposed Autochrome gamut:
This process, with its narrow gamut of colors, lacks the ability to capture reds and saturated blues, but it produces nice shades of pink and violet, as well as prominent orange and pale cyan colors. You can see other attempts at Autochroming images in my article Autochrome here and Autochrome at my other blog.
My process uses custom ICC profiles, created in Photoshop, which are linked in my article Using ICC Profiles for Creative Color Control. If you download one of these profiles, you can use standard image editing software to convert your standard profile images to use my estimates of the Autochrome primary colors. The nice feature of this method is that once you convert an image to use the Autochrome profile, you can edit the image as much as you would like while never having the colors go out of gamut. Once you are finished editing, you convert the image back to the standard sRGB profile for viewing on your computer or for printing.
While this is satisfying and interesting, these images lack prominent characteristics of the original Autochrome process, namely, the dark “gamma” of the images as well as the pointillistic grain pattern which derives from the colored starch grains found on Autochrome plates. Certainly my work with the Autochrome color gamut is sufficient to produce interesting images with a limited range of colors reminiscent of Autochrome, but I think it would be interesting, and possibly valuable, to come up with a better digital imitation of the historical method.
I don’t claim that my Autochrome color profiles actually match the color gamut found in the original process, for the sample images found on the Internet are highly variable, but with common characteristics. But close is good enough. Likewise, if I attempt to imitate the pointillistic nature of Autochrome, then close will again be good enough. It is my intention to create a method that is adequate.
In the article What is Autochrome? at the website of the Šechtl & Voseček Museum of Photography, you can see a microphotograph of the starch grains found in Autochrome, as well as many sample images and a description of the process.
The grains are generally round, bunched together in clusters, with a small amount of black pigment between the gaps. This grain, somehow, needs to be reproduced in Photoshop for our process. Now producing a photorealistic imitation of these grains would be very difficult, impractical, and would tax the resources of my computer, so I will produce a pixelated version instead, with clumps of square instead of round grains.
I’ve read a number of estimates of the sizes of the starch grains, from 5 to 10 microns in size, and some say that the process used 4 million grains per square inch. For our purposes, knowing the number of grains per linear inch is important, and various authorities state 1700, 2000, and 2500 grains per linear inch.
The Autochrome plates were manufactured in a wide variety of English and metric sizes. The pointillistic ‘look’ of the images is quite prominent on smaller plate sizes, but is not particularly noticeable on digital images made from larger plates. For our purposes, we’ll imitate the characteristics of a small plate, 3-1/4x4 inches in size, and use the intermediate value of 2000 grains per linear inch, which gives us an image 8000 x 6500 grains in size, or a 52 megagrain image. Please note that the color grains in Autochrome are randomly scattered, and so there is significant clumping of colors, reducing the final resolution and color accuracy of the image. Because it does not have the regular pattern of the Bayer sensor found in most digital cameras, Autochrome does not illustrate aliasing or the Moiré effect.
Now I have no idea as to the size of the light-sensitive silver grains found in Autochrome, but I’d think that the silver grains were smaller than the color grains, otherwise there would be a significant loss of saturation. I’m not sure how much this matters, but from my experimentation, very many color grains improve the final results. My digital camera is rather aged, and produces images 3008 x 2000 pixels in size, and using a grain pattern that size produces images that have an objectionable amount of grain. If we have a target of 6500 grains along the short edge of my image, then I will upsize from 3008 x 2000 to 9776 x 6500, preserving the aspect ratio, while imitating the grain pattern found in the smaller sample images. This would be roughly equal to an Autochrome plate 3-1/4 x 4-7/8 inches in size.
The difficult part of this process is creating a pixelated version of the color grain pattern of Autochrome, and it needs to be made in exactly the same number of pixels as the upsized image. As each manufacturer makes slightly different aspect ratios of images — and even some RAW converters will vary the number of pixels, then you will have to make your own grain pattern.
This is a highly-zoomed portion of a grain pattern that I made. Each pixel substitutes for an Autochrome grain, and like the original Autochrome, the grains are clumped together instead of being uniform. It doesn’t matter that it uses the standard sRGB primary colors, and not those of Autochrome.
Here is how I made it in Photoshop CS5:
- Create a new image the precise size as your upsized digital image: for me, that is 6500 x 9776.
- Fill the blank image with 50% gray.
- Select the red channel.
- Select the menu item Filter - Noise - Add Noise...
- Adjust Amount to 50% and specify Uniform Distribution.
- Select the menu item Image - Adjustments - Threshold...
- Adjust Threshold Level to 173. If you check the histogram, you should see that 33.3% of the pixels are white; if not, you may have to adjust the Threshold Level slightly.
- Select the Green channel, and add the same amount of noise as before.
- Select the menu item Image - Apply Image...
- Use the Red channel, check Invert, and set Blending to Darken. This masks out the red pixels created in the previous step.
- Use the Threshold menu again, setting Threshold Level to 132. One third of the pixels are white. You may have to check the histogram to be sure: unequal percentages will throw off your white balance a bit.
- Select the Blue channel.
- Using Apply Image, apply both the inverted red and green channels, using Darken Blending, to mask out the red and green pixels.
- Select the menu item Image - Auto Tone to quickly turn the remaining gray pixels to white.
- Select the RGB channels, zoom into your image, and you will notice uniformly scattered red, green, and blue pixels.
- Save the image as a TIFF file to preserve the colors.
- If you haven’t done so already, download the Autochrome ICC profile from the article Using ICC Profiles for Creative Color Control, and install it in Photoshop.
- Select the menu item Edit - Assign Profile... and select Autochrome. This will change the sRGB primary colors to Autochrome’s primaries.
- Take your target image and upsize it to be equal in size to your grain pattern image.
- Either Assign or Convert your target image to the Autochrome profile. Read the article Using ICC Profiles for Creative Color Control for a discussion of the pros and cons of both methods.
- Edit your image as you would like.
- Drag the grain image on top of your target image and set the blending mode to Darken.
- Your image will now look terrible. Do not have fear.
- Flatten the image. It will now be rather dark, but will have textured grain, which you can see if you zoom into it.
- Shrink your image to a more manageable size if needed. The method you use will have a great effect on the grain in the image: Bicubic Sharper appears to do the best job.
- Convert the image back to the sRGB profile.
- Adjust the Levels to brighten the image a bit, but you may not want to clip any of the highlights.
Before:
After:
Before:
After:
Tuesday, February 28, 2012
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.
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.
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