SRGB V RGB Help

Started Oct 22, 2007 | Discussions thread
Matthew Thomas Regular Member • Posts: 170
Adobe RGB if editing in 16bit, sRGB if in 8-bit

Use Adobe RGB if you don't mind converting your Raw files to 16bit color. This does allow for a few more colors that can't be used in sRGB. If you are shooting in RAW, it doesn't matter which settting you use in your camera since the actual color space is only defined once you convert the RAW file. The only effect the in-camera setting has is how it generates the JPEG preview of your RAW file.

If you shoot mainly in JPEG, don't even think about Adobe RGB. Again, ADOBE JPEG OFFERS NO BENEFIT TO JPEG OR OTHER 8BIT IMAGES. This is not my opinion, it is fact based on simple mathematics.

I will explain how Adobe RGB is not recommended for 8bit color modes (such as jpeg, 8bit tif or basic psd's). This is because most of the 256 available shades of grey aren't used in 99% of images.

Think of it this way: In 8-bit modes, your file only has 255 levels of color for each of the 3 color channels. This results in a theoretical 16.8 million color posibilities. In theory...That is assuming that you acutally use all of those colors. Different color spaces determine how all these colors are used, or unused.

For Example, the color space you use determines how each of these 255 levels are mapped. In a narrow color space like sRGB, the highest saturation of red from most scenes will be near the 255 mark in the red channel (with 0 being the least saturated as white and a 100 or so being pink between the two).

This is OK for most images since in nature, it is rare to see reds that are more saturated than this (neon or black light effects are an obvious exception). As a result, a distinct advantage of using sRGB is that with most scenes, it will be able to USE IT'S ENTIRE range for colors less saturated than our most saturated red. This means you will have 250 or more levels from red to pink to white. This results in less banding because the difference between steps of color are smaller. When used in 8 bit color modes (only 256 levels of grey) sRGB has way less banding in subtle gradations such as blue skies, etc.

With Adobe RGB in 8 bit images, the red color that would have been close to the highest number 245 or so) in sRGB is no longer placed near the edge of the range of the image. The same red would be closer to 150 or so. This means that there is room for more saturated color above the red, but in most cases such brilliance simply doesn't exist in the scene. As a result, many of the bits of the image are wasted and not used at all. The entire range between, say, 150 and 255 are unused. This also means that there are now less bits left for the less saturated colors that are actually present in a typical image. This is sometimes OK but with less steps between white to pink, then red, banding and digital noise becomes more and more likely. Furthermore, if I choose to photoshop the image and adjust exposure significantly, there may be even less steps between colors after I do this, further enhancing banding and noise. This is the biggest limitation of wider RGB spaces such as Adobe RGB in 8 bit modes: Banding and Noise!

Now before you decide to avoid AdobeRGB forever, consider that IF YOU SHOOT RAW, you can decide to convert your image into 16bit color mode. This allows thousands of levels, not just 255 as in 8 bit. In Photoshop's 16-bit mode, you can reduce your bandwudth with Adobe RGB, and still have many, many steps between our red color and pink and white. With 16bit images, the advantages of Adobe RGB become very obvious. You can have more saturated red than the red we originally shot (by adjusting and boosting saturation in Photoshop) yet still have a decent number of steps below the red leading from pink to white, thanks to the additional steps provided by 16-bit color mode. In this mode, banding is mostly a non-issue since even after cutting your available bits in half, there are still hundreds of available steps for each color channel.

Warning: If you use Adobe RGB with 16 bit mode, be sure to CONVERT it to sRGB before posting it online or sending it to anyone that doesn't use Photoshop or InDesign. Most browsers will display all JPEG images in sRGB, regardless of the setting you used in Photoshop.

You need to convert to this space for reliable representation of your image to the public. This should be done with the Convert to Profile command in Photoshop, not the Assign Profile Command. Assign Profile will not modify the actual pixel color values. Merely Assigning profile will seem to have little effect in Photoshop, but as soon as you take it to a web browser, the browser will interpret the images as sRGB. This will result in a HUGE drop in saturation and contrast. It is ugly, so don't do this.

If you plan on sharing your photo with someone that uses a program that doesn't understand Adobe RGB color space, you MUST modify the pixel data using the Convert to Profile command. Convert it to a narrower color space like sRGB for the widest compatibliity. You do this at the expense of possibly losing some of your most saturated colors in the image (if they exist). Such over saturated colors will basically clip at the most saturated point in the image but most users of web browsers, etc will not mind this. This means there will be little to no detail in the most saturated parts of the scene. A common remark with such images is a cartoonish look but it can be a nice effect and it is far superior to posting the image in AdobeRGB, which will destroy your images' contrast and saturation.

One the other hand, converting an sRGB image into Adobe RGB offers little to nothing to a photographer. It would only be useful if you are adding pantone spot colors to your image (added in a design program) and you want those colors to maintain their vibrant saturation alongside your natural image..

Lastly, you may keep in mind that IF YOU SHOOT IN RAW, you can choose the color space that is most appropriate for your image when opening the image in Photoshop Raw converter. This way, you can reserve your decision to use Adobe RGB in images that have many saturated colors, and heavily contrasty scenes. You can do this only when necessary. I would say that for most (95%) of images that involve human skin tones, sRGB is more than adequate to capture the colors of a scene. And, as a general rule of thumb, YOU SHOULD ALWAYS USE THE NARROWEST COLOR SPACE THAT YOUR IMAGE REQUIRES. This is usually sRGB. This is to reduce banding and noise. Adobe RGB will be necesary for a small number of images which use very saturated colors, and ProRGB could theoretically be useful if you shoot scenes with black-lights and neon.

As for what this means to printing:

Wide color spaces like Adobe RGB (and the even wider ProPhoto) are intended to maintain detail in areas of extreme color saturation. However, these extreme colors are really not visible on a computer monitor since very very few monitors can show such saturation. If you pay less than $3K for your monitor, it will not show much detail beyond those achieved by sRGB. The newer LED screens can approach Adobe RGB so if you have this type of screen, rejoice. You chose wisely. These are mystery colors that inks like hexachrome presses can produce and pantone simulations can also create them, but they are not typically found in the standard CMYK pallette.

Here's the good news: the current pro photo inkjet printers can usually produce most of the colors in Adobe RGB, so there is an advantage to using it if you print your own images on a newer photo printer such as the Canon Pro9000 or Epson 2400.

Experienced (and colorsync aware) Graphic Designers also use Adobe RGB for designs because they allow for the integration of the more saturated Pantone colors to be blended with their basic CMYK elements. Again, this is possible because Adobe RGB allows more saturation than other color spaces which is also the advantage of using Pantone colors in most cases.

These are the main reasons to use wide color spaces. If you don't know why you need a wide color space, it is usually best to assume you don't.

I've had several beers while writing this message so forgive me for letting it get out of hand. I hope it was helpful to you.

Thanks and I look forward to your feedback.
--
Matthew Thomas
Partner / Multimedia Director
ThomasArts, Inc.

Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow