Colorspaces

In this discussion i going to demonstrate the differences between the various RGBs, CMYK and LAB colorspaces with articles, studies and own experiences.

——————————————————————————————-

sRGB or AdobeRGB?

It’s a very interesting article from an insider:

INTRODUCTION

The same old-wives-tale about Adobe RGB having a broader range of colors has been circulating on the internet since the 1990s.

It does in theory, but not in practice.

I know this stuff. Did you know I conceived the world’s first dedicated digital colorspace converter chip, the TMC2272, back in 1990 when I worked at TRW LSI Products? I’ve been working with the matrix math, hardware and software that does this for decades. I also coined the word “gigacolors,” for use with 36-bit and 48-bit color data. I was only kidding, but the word is still used. TRW LSI was a small, ultra-creative division of TRW, and I got away putting the same mirth I use on this website into the datasheets I wrote. The industry copied us and the word lives on.

10 years ago when I was able to start doing this at home I also was all excited about Adobe RGB and a slew of other whacky, innovative color spaces. After some experimentation, even I discovered that default sRGB was plenty for everything I did, and eliminated the chance for grave errors.

Adobe RGB is irrelevant for real photography. sRGB gives better (more consistent) results and the same, or brighter, colors.

Using Adobe RGB is one of the leading causes of colors not matching between monitor and print.

sRGB is the world’s default color space. Use it and everything looks great everywhere, all the time.

Adobe RGB should never be used unless you really know what you’re doing and do all your printing yourself. If you really know what you’re doing and working in publishing, go right ahead and use it. If you have to ask, don’t even try it.

If you’re one of the few a full-time career professional photographers left standing and shoot for print, by all means shoot Adobe RGB, but if you’re a very serious amateur, beware.

Adobe RGB theoretically can represent a wider range (gamut) of colors, however:

1.) Adobe RGB requires special software and painstaking workflow not to screw it up. Make one mistake anyplace and you get dull colors, or worse. You cannot use Adobe RGB on the internet or for email or conventional photo lab printing. If you do, the colors are duller.

2.) I’ve made Lightjet, Fuji Supergloss and inkjet prints of 100% saturated ramps in both color spaces. I saw the same color range in print with each colorspace. I saw no real gain of any wider gamut in practice, even with these special tests.

I didn’t see any of these printers have the ability display any of the extra gamut potentially represented by Adobe RGB.

Details

sRGB is the world standard for digital images, printing and the Internet. So long as you haven’t screwed with anything, you and the world are shooting in sRGB.

Use sRGB and you’ll get great, accurate colors everywhere all the time. Like what you see in my Gallery and the top grad (widest rainbow) above? That’s all coming to you in sRGB. Use sRGB and you’ll automatically get great, saturated and accurate color everywhere. See also Color Management is for Wimps.

sRGB is specified in IEC 61966-2.1, which you may also see when examining color profiles. That gobbledygook means the same thing as sRGB. (sRGB uses ITU BT Rec. 709 primaries and a gamma of 2.2, same as most kinds of HDTV.)

Adobe RGB squeezes colors into a smaller range (makes them duller) before recording them to your file. Special smart software is then needed to expand the colors back to where they should be when opening the file.

Since Adobe RGB squeezes colors into a smaller range, the full range represents a broader range of colors, if and only if you have the correct software to read it.

Played back on most equipment, the internet or email, the colors look duller, and when played back with the correct software, the extra chroma gain required adds a little chroma quantization noise.

This is the example above. The bottom grad is what an Adobe RGB file looks like when interpreted as sRGB, which is what happens over the internet, email, or most printers unless you’re printing directly at home from Photoshop. Printed correctly the Adobe RGB grad looks the same as the sRGB grad, so I asked myself, why bother?

If you use Adobe RGB you will have to remember to convert back to sRGB for sending your prints out or sharing them on the Internet. Otherwise they look duller than sRGB!

If you have the right software to re-expand the colors you theoretically might have a slightly broader range of colors. However, if at any point in the chain you don’t have the right software and haven’t attached the Adobe RGB profile you’ll get the duller colors as recorded!

Web browsers don’t have, and print labs rarely have, the right software to read Adobe RGB This is why people who shoot it are so often disappointed. Even if a place has the right software, if you forget to add the Adobe RGB profiles to your files these places will read them incorrectly and you’ll get dull colors.

Adobe RGB may be able to represent a slightly larger range of colors, but no screen or print material I’ve used can show this broader range, so why cause yourself all the trouble? I’ve experimented with 100% saturated grads in these two color spaces and never seen any broader range from Adobe RGB either on my screen or on SuperGloss Light jet prints.

Worse, if you’re the sort of vacuum-operating geek who wants to shoot Adobe RGB because you read about it in a magazine article, did you realize that because the colors are compressed into a smaller range that there is more chroma quantization noise when the file is opened again? Ha!

Keeping people lost and confused sells more magazines and more new equipment, which supports magazine advertising. That’s why you see so many articles on Adobe RGB elsewhere.

original source

AdobeRGB and sRGB actually have the same number of colors. The difference is that AdobeRGB has a wider, more spread out array of colors. The advantage to this is that there are some colors that AdobeRGB can display on the outside of the array which sRGB clips. But there is also an advantage to sRGB’s tighter array of colors in that there is more subtle changes between it’s colors.
A more appropriate analogy would be two boxes of crayons, each having let’s say 64 crayons for simplification. AdobeRGB’s box of crayons includes a larger variety of colors, including some neat ones like neon green that aren’t in the sRGB box. But with the sRGB box, you get more variations in it’s colors such as red, light-red, light-light-red, medium-light-red, etc., which aren’t all present in Adobe’s box of crayons.

SO: What’s the more important for you?
“More” color (AdobeRGB) or the same as you shooted and finer gradiented color (sRGB)…

For web use & real photography sRGB is the recommended, as long as for print is the AdobeRGB.
——————————————————————————————-

And what’s up with the ProPhotoRGB?

To answer that question, let’s first look at just how big “big” is. Shown here is another diagram along the lines of those I used last week. In addition to the shapes outlining the gamut for sRGB and Adobe RGB, I have added a white line showing the extent of ProPhoto RGB’s gamut as well as an indication of the typical gamut of an Epson desktop printer on glossy paper (the gamuts of matte papers tend to be somewhat smaller). ProPhoto is huge. While Adobe RGB covers about twenty percent more area than sRGB, ProPhoto RGB is about twice the size of sRGB. Better than fifty percent bigger than even Adobe RGB.

Indeed, ProPhoto is so big, it actually includes some colors that are beyond the range of human perception.

It is the only one of the three though that encompasses the entire gamut of the Epson printer shown. sRGB severely clips the Epson gamut in the cyan to green region (bottom left) and yellow-orange region (top). Adobe RGB can still clip some very saturated yellows but does cover all the greens, and green is a very important color being in the middle of the visual spectrum and very prevalent in nature. It seems tempting then to use ProPhoto RGB in order to not lose that area of yellow. But if we do, we have to accept the fact that we also will be encompassing colors we can’t even see, never mind print.

Just as Adobe RGB and sRGB contain the same number of colors as dictated by the limitations of how they are represented in 8-bit and 16-bit mode, ProPhoto too has to live within what the numbers are capable of. 16.7 million colors in 8-bit and 281 trillion colors in 16-bit mode sure seem like a lot. But given how much bigger ProPhoto is than the alternatives, it may be worth considering whether we want to devote so many of them to colors that seem to serve no purpose. Even in 16-bit mode, this should give us pause for thought. That’s a pretty high price to pay to not lose a few shades of yellow-orange.

But technology continues to advance, and just because we can’t print much beyond Adobe RGB today doesn’t mean we’ll always be so color challenged.

Indeed, the advent of digital cameras allows us to easily capture colors that Adobe RGB can’t represent. While you may be limited to sRGB and Adobe RGB when shooting, the use of RAW mode gives access to everything the sensor recorded. Adobe Camera Raw (when using Photoshop, not Elements) allows you to select what color space you want to convert your RAW files to. In addition to sRGB and Adobe RGB, the list includes both Color Match RGB and ProPhoto. Color Match is a traditional color space with a gamut similar to that of sRGB used on early Macintosh computers and isn’t of much interest today, but ProPhoto can come in handy.

Shown here are three versions of the same shot taken at Sylvan Lake in South Dakota’s Custer State Park. I opened the RAW file in Adobe Camera Raw and turned on the highlight clipping option, then made three screen captures, each with a different color space selected. The bright red shows the portion in each where clipping would occur. As you can see, sRGB loses quite a bit, while Adobe RGB comes much closer. Only ProPhoto RGB is able to encompass all the colors without clipping. The pre-dawn sky itself is somewhat pink, but what matters here is the red clipping display, not the pink sky.

By converting your RAW files into ProPhoto RGB in Adobe Camera Raw you preserve more of what the sensor actually saw. Once you open them in Photoshop though, you need to decide what to do next. If you keep them in ProPhoto, you’ll have files that in the future may yield better prints than if you settled for Adobe RGB. But the gamut of ProPhoto is so large that, unless you are careful, you may need to contend with banding and other artifact problems, even in 16-bit mode. A definite dilemma.

Some photographers have adopted a ProPhoto RGB workflow but so far I haven’t gone that far. What I do do though is convert images to ProPhoto RGB if Adobe RGB shows excessive clipping. After opening such images in Photoshop, I then convert to Adobe RGB using Perceptual rendering intent which compresses the gamut rather than clipping it. Once the image is in my regular Adobe RGB working space I can then selectively adjust saturation to restore the image to how I want it to look.

In an 8-bit world, sRGB represented the best compromise between gamut and usability. Now that we can use 16-bit for most things, Adobe RGB rules the day. Once the world moves from 16-bit to 32-bit images, I will undoubtedly start using ProPhoto as my working space. For now at least, I’m being somewhat cautious. I use ProPhoto where it definitely makes sense to, and then retreat to the safety of Adobe RGB. As I gain more familiarity with ProPhoto, its charms are indeed alluring and it is possible I may adopt it completely before the era of 32-bit, but not yet.

For the curious, the shapes shown this week and last represent the two-dimensional gamut projections as graphed in LAB mode. LAB is a representation of color that is considered “perceptually uniform” in that the distance between any two colors is proportional to how different the two colors appear. As such, it is particularly useful for the purpose at hand since the area of each outline is therefore visually proportional to the colors each contains. Gamut is actually a three-dimensional function since, in additional hue and saturation represented in these two-dimensional shapes, brightness also plays a role. But the screen on my monitor is itself two-dimensional so I’ve limited myself to what I can show without resorting to special browser plug-ins and such.

By the way, don’t even think of using ProPhoto RGB in 8-bit mode.

original source
———————————————————————————————

My Personal Opinion

I say if your camera able to work in RAW, then use it (If can’t then work in sRGB).
When you open the RAW with Photoshop Camera RAW, select the ProPhotoRGB colorspace and 16bit. It’s the best performance for your shot.

But when you render the image to JPEG, you lose the quality of PhotoRGB. Why? Because JPEG can’t work above 8bit. It’s maybe seamless for you, but the consciousness…

What’s the key? Check out our next topic.
——————————————————————————————–

RGB & CMYK

Computer monitors emit color as RGB (red, green, blue) light. Although all colors of the visible spectrum can be produced by merging red, green and blue light, monitors are capable of displaying only a limited gamut (i.e., range) of the visible spectrum.

CMYK versus RGB color spectrum
Whereas monitors emit light, inked paper absorbs or reflects specific wavelengths. Cyan, magenta and yellow pigments serve as filters, subtracting varying degrees of red, green and blue from white light to produce a selective gamut of spectral colors. Like monitors, printing inks also produce a color gamut that is only a subset of the visible spectrum, although the range is not the same for both. Consequently, the same art displayed on a computer monitor may not match to that printed in a publication. Also, because printing processes such as offset lithography use CMYK (cyan, magenta, yellow, black) inks, digital art must be converted to CMYK color for print. Some printers prefer digital art files be supplied in the RGB color space with ICC profiles attached. Images can then be converted to the CMYK color space by the printer using color management methods that honor profiles if present; this helps preserve the best possible detail and vibrancy.


Red, Green, Blue – Additive colors


Cyan, Magenta, Yellow – Subtractive colors


Visible color spectrum with print gamut

Some printers may prefer your files be delivered in RGB with ICC profiles attached, as this allows the printer to use color management methods when converting to CMYK. Other printers may prefer your files in the CMYK (Cyan/Magenta/Yellow/Black) mode, as this is the mode required for the printing process. If an RGB (Red/Green/Blue) file is submitted, it must be converted to CMYK for print.

It can sometimes be difficult to visualize the reason for color shift in color space conversion. The best way to see the color differences between the CMYK and RGB color spaces is to look at a color gamut comparison chart. The chart to the left plots the visible color spectrum as the large “horse shoe” area, and within this is a plot of the CMYK colors, and the RGB colors. You can see that in some areas the RGB color space is “outside” that of the CMYK space. It is these colors that will be affected by a conversion from RGB to CMYK.

Desktop scanners & color space
Most desktop scanners, digital cameras, and video capture systems save files as RGB and the conversion of RGB files to CMYK can be done in many ways (see how to convert RGB to CMYK). RGB converts to only CMY directly. However, when printing, we must add black ink and in doing so must cut back on some color. The Undercolor Removal (UCR) setup will help control this ratio so that a maximum ink density for the four colors will be 300% when printing on a coated paper stock.

Spot colors
Digital art that is comprised of spot colors (e.g., special colors: any colors that are not CMYK process colors), generally require conversion to the CMYK color space to enable file use. Because color gamut’s for spot color libraries, such as those associated with the Pantone Matching System (PMS), usually extend beyond the ranges of the CMYK color gamut, some spot colors may not be represented effectively using CMYK process inks.


Halftoning screen angles 133dpi 40% screen enlarged

Image halftones
In offset lithography, the density of CMYK inks can not be varied in continuous fashion across an image, so a range is produced by means of halftoning. In halftoning, translucent CMYK ink dots of variable size are printed in overlapping grids. Grids are placed at different angles for each of the ink colors. Smaller halftone dots absorb less light; thus, as a result of an increase in the amount of reflected light, apparent density is decreased and the object appears lighter.

original source
——————————————————————————————-

LAB

A Lab color space is a color-opponent space with dimension “L” for lightness and “a” and “b” for the color-opponent dimensions, based on nonlinearly-compressed CIE XYZ color space coordinates.

Unlike the RGB and CMYK color models, Lab color is designed to approximate human vision. It aspires to perceptual uniformity, and its L component closely matches human perception of lightness. It can thus be used to make accurate color balance corrections by modifying output curves in the a and b components, or to adjust the lightness contrast using the L component. In RGB or CMYK spaces, which model the output of physical devices rather than human visual perception, these transformations can only be done with the help of appropriate blend modes in the editing application.

Because Lab space is much larger than the gamut of computer displays, printers, or even human vision, a bitmap image represented as Lab requires more data per pixel to obtain the same precision as an RGB or CMYK bitmap. In the 1990s, when computer hardware and software was mostly limited to storing and manipulating 8 bit/channel bitmaps, converting an RGB image to Lab and back was a lossy operation. With 16 bit/channel support now common, this is no longer such a problem.

Additionally, many of the “colors” within Lab space fall outside the gamut of human vision, and are therefore purely imaginary; these “colors” cannot be reproduced in the physical world.

The LAB color space is the only “device independent” color space in Photoshop, and when used correctly, it is the only one that will allow the user to have the best color match from capture to display to print.

Simply put – the LAB color space is the only one representing the way the human eye sees color. And that is the most important thing when it comes to ensuring color match throughout the process.

Let me explain what “device independent” means:

Simply put, “device independent” color space is one that regardless of which device is used the human eye will always see the exact same color.

RGB an CMYK color spaces are component based spaces. Whet it means is that when a color is “created” it is made up of certain amounts of each component. The problem is that different devices use different components. Take for example two monitors. Their RGB phosphors will be different, so despite the fact that they may display same quantities of RGB components, the human eye will see two different colors. The same is true for CMYK – take two printers, and same CMYK amounts will result in the eye seeing two different colors.

That is not the case with LAB. When the same LAB value is measured on any number of devices (which will probably require different component, RGB or CMYK, to do that, which is what device profile do), the human eye will always see exactly the same color.

original source

Advertisements

About this entry