Photography 101 – Color Mapping for Images

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Color Mapping – what color space is appropriate for certain photographs?  This is a very important part of photography and graphic design and is only going to become more important as new technology arrives.  Once you view your images on the latest monitors, you will see that this is something any good photographer is going to have to take into consideration while processing their images.

I am writing this blog to simplify the process for myself and to remember these couple of facts:

Let’s say you  have a  great photograph of a landscape and you are curious about which color space is the best fit for this image based on either sRGB, Adobe RGB or ProPhoto RGB. It may take a little to get good at judging the color spaces and and pre-visualize how you’re going to process that image to get the result you’re looking for, but this is what will make you a great photographer.

There are a few things to consider based on how you are going to use your images.  Will they only be shown on the web, or are you planning to print it someday?

So we already know that all color modes are based on 3 channels, red, green and blue.  And we also know that basic color information tells us that an image in an 8-bit mode refers to the availability of 255 colors in each channel, which equals 16.7 million possible colors, and a 16-bit image has 65536 colors in each channel offering up the possibility of over 281 trillion colors!

sRGB has the lowest gamut of color range and works well in low end monitors.  It is about 20 percent less color space than Adobe RGB and half that of ProPhoto.  It used an 8-bit mode and will literally eliminate some color saturation.  Most monitors capacity can only render images in this mode and is okay if you are not going to do any editing or printing of your work.

Adobe RGB uses the same amount of colors as sRGB, only spread out a little bit rendering a more saturated color.  This is a more acceptable mode for editing or printing images.  If there is banding or other funky artifacts, you will need to open your images and work in ProPhoto. An image that was rendered in sRGB mode and viewed in an Adobe RGB monitor will look washed out.    Again, this takes a little while to discover, but the best amateur photographers and pros consider these things.

If you are going to display your images only on the web, images shot in JPEG mode and rendered in 8-bit mode might be sufficient.  If you shoot in RAW, then your images can be rendered in any of the available color spaces.

SHOOT IN RAW!

If you want to print your images, or edit them, you should be shooting in RAW and edited in 16-bit mode. 16 bit mode does not allow more saturated colors than 8 bit mode, but rather more colors in between the existing 8 bit colors. It is actually better to do all you image editing in 16 bit mode especially when working with a large gamut color space.

RAW files can be converted to whatever color space you decide when you import it into an image editing program. Also note that most digital SLR sensors can capture colors that are outside the Adobe RGB color space, which leads us to ProPhoto RGB.

ProPhoto RGB has about 50 percent bigger range in color than Adobe RGB. Some Epson printers are capable of printing colors outside the Adobe RGB color space, namely in the orange and yellows. ProPhoto RGB covers all of these colors, but also some that are not even visible, let alone printable. In fact, the color space is so big that even in 16 bit mode, you risk banding and artifacts due to the “gaps” between the colors. Generally, you only want to use ProPhoto if you see clipping in the Adobe RGB color space.

Once you have your file open in ProPhoto RGB you have to be careful. The huge size of the color space and the size of the gaps between the colors means that you risk banding and other rounding errors if you are not careful. Do not even think of using ProPhoto RGB in 8 bit mode. The results are disastrous.

The histogram is a bar graph that shows the amount of each brightness or color intensity level in an image and illustrates the image’s overall tonal range.  This graph can be seen in numerous places in a variety of photo editing software.  Viewing histogram in addition to viewing the image itself, can be helpful in determining how to adjust an image for its intended purpose.

A histogram often looks like a solid shape of a mountain range with a jagged top, but it is actually made up of a series of adjacent vertical bars that measure the amounts of each brightness level in an image.  The taller the bar in the graph, the more of its tone is present in the image.

An image with mostly white clouds generates many tall bars on the right side of the graph, representing the lighter colors.  Add some black, and the histogram will pick that up on the left side.  In between these two are mid-tones and shades.  A histogram with bars all the way across means that the image contains all the available brightness levels possible, which often makes an image appear full of detail and depth.  Making changes that cause the bars to appear across the entire width of the histogram is a good objective if detail and depth are intended for the image, which is usually the case for photos of people and scenery.

When depth and detail are the goals, avoid huge gaps in the histogram.  If there is a limited amount of color in your image, then there will be an acceptable amount of gaps.  There is no one right histogram for each image.  Again, this comes with experience and practice.

Histograms measure the pixels in an image in numerous ways.  Practice working with a histogram by converting your image beween the different color modes if you want to get a real good grip on this concept.

I am finding that the best process for me is to shoot in RAW, open the image using the ProPhoto RGB color space, covert it to Adobe RGB while keeping it in 16 bit mode. This way I am able to do a lot more editing without the risk of errors and the image won’t be degraded. Also keep in mind that you want to convert to Adobe RGB using the Perceptual rendering intent. Doing this will compress the color gamut (range) rather than clipping it.

So, if you want to get the absolute best out of your images, shoot RAW and process as you need to. Stick with Adobe RGB and 16 bit mode for your editing to maximize your image potential and avoid problems.  Become an expert using the histogram.  With new technology, it is imperative that any graphic design or photography students understand the difference in the color modes.

I am pretty sure we will be seeing additional color modes in the future……