Strodav Loc: Houston, Tx

Color spaces like CIE, L*a*b* (CIELAB), CIE XYZ, Adobe rgb, srgb, ... are imperfect mathematical models of the human visual system or restricted parts of the human visual system. Of course we see colors represented by a device independent color space every time you open your eyes and look at nature. It's just that we don't see those colors accurately reproduced on our monitors or in our prints because they do not have the same gamut as the human visual system, but they fill enough of the gamut so our minds see them as representing the original scene.

I always keep the raw files from my cameras as they are the widest gamut captured and maybe some day there will be a reasonably priced monitor or printer that can truly reproduce all the data. But for right now, a very important part of PP is reduce the camera's color space to fit the output devices we have, which most of the time becomes srgb. It's not only colors, but dynamic range as well, which are all part of these color spaces. It's the L in Lab and the Z in XYZ for example. The diagram below gives you a good idea of the colors we can see that cannot be reproduced today. I un-apologetically stole it from a Wikipedia.org article on color spaces. Note the ProPhotoRGB color space is actually larger than the CIEXYZ color space, so it contains colors humans can't see. Why? It's a simple engineering principle to keep as much original fidelity as possible then funnel it down for your output device when needed.

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amfoto1 Loc: San Jose, Calif. USA

Yes. ProPhoto is currently the widest color space commonly available and working in it with 16 bit files such as TIFFs and PSDs will give the best quality edits. Adobe RGB is pretty close, if preferred or not able to use ProPhoto for some reason.



Yes. This is best because sRGB is much more widely used than Adobe RGB. Once you upload an image to the Internet, you no longer control how and with what it will be viewed. Many browsers and other software do not properly interpolate Adobe RGB, so it's best to convert to sRGB. Also be sure to reduce from 16 bit to 8 bit. Doing these things after all your image editing and sizing has been done usually shows very little loss of image quality. It also results in smaller, more manageable files that display quickly and smoothly with a wide variety of devices and software.



No. This is not the case. You usually should use sRGB color space. I know some printers can handle Adobe RGB and even 16 bit files, but there's almost always no gain in image quality. it just makes for slower printing and may even waste ink. Many printing services and most photo-quality inkjets specify sRGB 8-bit files (usually JPEGs).

One difference between printing and online display is the pixels per inch you should use. For online display I usually set 100 ppi. For printing I usually use 300 ppi, which results in a larger file. These aren't hard and fast numbers.... some monitors display 96 ppi, while others such as 4K may show as much as 130 ppi. It's the same with printing... the larger the print and the farther away it will be viewed, the lower the ppi can be. 300 ppi is more than enough for even modest sized, closely viewed prints. 240 ppi is even usable. But if making a larger print where viewers will need to step back to see it, you might use 170 ppi or even less. An extreme example, a bill board that's viewed from dozens of feet away might only be 40 ppi!

I'm not aware of ANY "even smaller color space" that's being used for photo printing purposes. I wouldn't even know how to find or specify one in my software!

There IS a "CMYK" color space that's used for commercial printing purposes. For example, CMYK is used with offset printing where there will be separate plates made for each of the color channels and black (C=cyan, M=magenta, Y=yellow, K="key" or black). Perhaps this is what you've heard about. It is NOT "smaller" than sRGB and is NOT something that's commonly used by photo printing services or appropriate for printing yourself with a photo-quality inkjet.

There are a few other specialized color spaces, which I don't know anything about.

I like to keep it simple:

1. Camera set to Adobe RGB, though it really doesn't matter when shooting RAW.
2. Work on 16 bit images in Photoshop either in ProPhoto or Adobe RAW color space.
3. Size images to 100 pixels per inch for online purpose, 300 ppi for printing (unless otherwise specified).
4. After all the work is done, reduce images to 8-bit, sRGB for either online or printing purposes (unless otherwise specified).

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

But 100 ppi on a 1920x1200 display will not be the same as a 5K display at 5120 × 2880. I use the HD standard that Facebook and others use - 2048 px on the longest side. And for prints, I use the maximum number of pixels in the image, and if the print is really large I use the guidelines - based on viewing distance and human visual acuity - found here:

http://www.photokaboom.com/photography/learn/printing/resolution/1_which_resolution_print_size_viewing_distance.htm

This saves chasing for more pixels when they aren't needed. But in all honesty I would love to be able to stand 10 ft away from a 4'x6' print of a spider and be able to count the hairs on the legs. Even if they were on the print there is no chance I'd be able to see them. Ever.

The resolution necessary for the perception of sharpness at 10 ft is only about 29 ppi or maybe as much as 100 ppi if there are OCD photographers in the viewing audience.

cbtsam Loc: Monkton, MD

Thanks to all for your erudite and helpful responses. You folks have been very responsive. And I don't mean to be difficult, but I've still got some somewhat practical questions.

(1) If I've understood it all, or at least some of it, as I play with my Photoshop sliders on my flower image in Prophoto, I might arrange a particular color that I find especially pleasing, lets call it SG (Sam's Green), which is such that, if I'd been working in Adobe RGB or sRGB, I could not have gotten there, because you can't find SG in those spaces. So that sounds like an advantage for Prophoto. However, if I put that image on the web in Adobe RGB, or more likely sRGB, there won't be any SG; it will be a subtly or not so subtly different green, or maybe not even a green at all to my eye, call it GG (Ghastly Green). So, for my flickr page, it seems I haven't gained anything by working in Prophoto; indeed, I may have lost something, since if I'd been working in sRGB from the start, I'd have pulled the sliders differently, to get something more pleasing to my eye and avoid GG. Now, I'll bet I'm missing something here, and I'd love to know what it is.

(2) I don't make prints at home. Instead, I use a local service that I'm told is pretty high end if not very high end; I've been using them since they made CibaChrome prints for me too many years ago to comfortably count, and they were pretty wonderful, as are the more recent inkjet prints. I give them a .PSD or .PSB file, with all the layers included, and they do the rest. Should I expect to see SG in the prints they make - assuming they use top end printers and really know how to use them - or is there a pretty good chance I could get GG?

(3) I read that, by working in Prophoto, I'm less likely, for example, to see banding in my skies when I really push the sliders. Could that banding, for example, appear when I convert to sRGB and post it to flickr? Could it show up in my "high end" print?

(4) Suppose I want to have a few copies of a vanity book made of some of my images. From what I'm reading in this thread, there's a good chance the book will be processed using CMYK, and certainly not Prophoto. And from the little research I've done online, it will be processed from an 8-bit file. So, again, will the image in my book exhibit SG, or could it well exhibit GG?

jdmiles Loc: Texas

Most internet printers use sRGB 8bit. However if you print at home with a modern printer such as the Canon 1000 you can print using Adobe RGB and 16 bit. The printer capabilities match Adobe RGB much better than sRGB.

The Capt.

I shoot in Adobe RGB at 14 bit - to get the most color.
Load into PS, Pro Photo 16 bit to prevent loss of color. - do any editing and maybe save a tiff.
Before sending in to print First change to Adobe RGB because I hear that Pro foto is to large for 8 bit color.
I am sometimes able to see a change when converting from Pro foto.
When in school studying how to make web sites they talked about dithering which is when the browser creates more colors for the image. I believe that this was just for Gif's but this was long ago and I can't remeber how this works.

Strodav Loc: Houston, Tx

If you shoot raw, the color space you select in your camera does not change the data, it is only an entry in the image file metadata header that may, or may not be used by your PP software. Your selected color space is applied in camera if you output jpg images, but the raw data is lost in the raw - jpg conversion process.

Re dithering. In some image processing systems "noise" can show up in patterns or be correlated to image content. This may happen during the scanning process (clicking the shutter), any part of the down stream signal processing path or even during image manipulation (PP). Dithering is a process adding random noise to the image to obscure these patterns. Also, dithering a clean image can actually make it appear sharper.

burkphoto Loc: High Point, NC

You might have your camera set to Adobe RGB, but that is just for a camera-created JPEG, or for the JPEG preview thumbnail stuffed into the raw file. That 14 bit raw file is just unprocessed data in the CAMERA's native color space. It gets converted to ProPhoto RGB (or whatever working color space you choose; Adobe RGB could be one of them) when you post-process the file.

Drbobcameraguy Loc: Eaton Ohio

Are you soft proofing your images before you print? I have no need to work in any color space other than sRGB because I can't print any higher the only place I can actually use or see the bigger color space is on my monitor. I shoot in raw and always keep an original raw file in case printers ect get better. But for practical purposes if I edit in a larger color space than sRGB when I soft proof I have a lot more work to do. I also save my soft proof adjustments so I can only use them to print. I used to want all the colors available but soon realized it just made more work and the average person can't really tell the difference unless they are laid side by side.

anotherview Loc: California

The monitor is back lit. The print is lit on its face by incident light.

The color space of sRGB allows for the image to look like to others the way it looked on your monitor. As best I can tell, the industry has put sRGB in place for this purpose.

When I save a file in the sRGB format, I set the size at 1 megabyte to ensure enough information for making a decent print. This approach has worked for me so ar.

I hope my limited comment helps some.

burkphoto Loc: High Point, NC

In 1996, HP, Microsoft, and several other big companies got together and agreed on sRGB as a color gamut they could all come close to matching with their office grade and consumer level devices. As such, it's a "lowest common denominator" color space. It's the Internet World Wide Web standard, the office printing and monitor standard, the default color space for in-camera generated JPEGs, and more. Almost everything supports it. That's a good thing and a bad thing, depending on what you need...

anotherview Loc: California

Thanks for explaining the sRGB file format more.