When a Color Image Should be Converted to Black and White


There are many good reasons for converting an image to black and white. Some images contain a lot of contrast and texture which can be better emphasized in black in white. Others have historic content that fits well with historic black and white looks. And sometimes an image is part of a series, and the best way to bring the entire series together is to process them all similarly in black and white.

But in the case of the image above, the main reason for conversion may not be apparent at first glance. Photographers have limited tools for controlling the color in their images. In some cases the only practical control of color is the veto: remove all chromatic information, and work from there. A look at the original image below should be enough to explain the reasoning in this case. It might make a good shock value image in color, but removing the bright tones certainly simplifies the image.


C. David Tobie

Tutorial: Editing Fall Foliage Photos

At the peak of fall foliage season the colors can reach fluorescent levels, by borrowing light from outside the visible spectrum and reemitting it in the red through yellow zones. Because of this, foliage photography requires careful editing to produce the type of image our eye recalls seeing. All too often people make the wrong adjustments, resulting in images that look false and unsatisfying. Lets look at a set of foliage photo adjustments, first by the numbers, and then tweaked to emulate the eye’s response, to see where photographers usually go wrong.

The Starting Point

Typically the camera is left to determine the best whitepoint, and to adjust at least one of the exposure parameters. The success of this varies with the subject matter, but often the result is not accurate, and the look is not ideal. In the image below, the default settings, when opened in Adobe Lightroom 4, produce a flat image, with insufficient color. Keep in mind that no color adjustment should be done to images without first calibrating your display.

Image at Defaults in Lightroom 4

Other elements in a fall foliage image still need to be correctly exposed and white balanced, for instance the twigs in this macro can’t be too red or too saturated, or the overall believability of the image will be lost. The best starting point for correcting camera settings for any image is with the SpyderCube. For this image the adjustments from shooting the SpyderCube in another frame earlier in the series are applied to the image. The camera default settings in Lightroom are shown next to the Cube-adjusted settings in the image below.

Default Settings, on left, and SpyderCube Adjustments, right

These settings increase the dynamic range of the image, making the midtones more dense, the shadows and blacks darker, adding punch to the image. Too often the assumption is that lightening fall foliage will make it “brighter” when the actual result is to make the colors weaker as they get lighter. Often, careful deepening of the midtones actually intensifies the foliage colors, as well as increasing the punch of the image as a whole. Note that the whitepoint of this image was fairly well estimated by the camera, so the color change caused by whitepoint correction, which can sometimes be quite significant, is minor in this case. The image below shows the result of applying these adjustments to the same photo.

Image with SpyderCube Adjustments applied

Camera Color Correction

Before making any visual adjustments to the image color, it is best to make global color corrections for the camera used. In this case I now applied a SpyderCheckr color calibration for this camera. The change to the image is subtle, and actually reduces the color saturation of the red channel, which is technically correct; but not necessarily in line with the artistic intent we have in mind for this image. Here is the SpyderCheckr adjusted version of the image below.

Image with SpyderCheckr Adjustments applied

Artistic Intent

Now that the dynamic range, white balance, and camera color have been corrected, I can make further adjustments to bring out the fluorescent nature of fall foliage in the image, while feeling comfortable that the overall corrections of the image will be in-line with the other images from the shoot that will be used in the same series. The lazy solution for fall foliage correction is to simply increase the global image saturation with the Saturation slider. However, many fall foliage images include greens and other colors, which will have their saturation increased along with the foliage colors, resulting in an image that the eye immediately sees as false.

The preferred solution is to adjust the saturation of the foliage color channels, while keeping an eye on the realism of the resulting image, and watching out for possible posterization in color transition zones. The image below shows a closeup of what happens to out of focus areas with color transitions when the changes between adjacent channels are excessive, and gradients posterize. The version at the bottom shows the final choices, which minimize this posterization. Note the reduction in banding around the green area.

Image with excessive adjustments between adjacent channels, top, and reductions to improve gradients, below

The next consideration is out-of-gamut colors. Its easy, when attempting to create the type of fluorescent results fall foliage can produce, to exceed the gamut of both your display and your printer. Gamut warning tools can be helpful in avoiding this situation, but the eye is the final arbiter. If further increase in the saturation of a color does not actually increase its saturation, and perhaps causes other side effects instead, then you are working outside the gamut of your display. Reduce the saturation increase you are producing until you can distinguish saturation changes with each slider adjustment.

Below are the SpyderCheckr HSL adjustments on the left, with the tweaked saturation settings on the right. These tweaked adjustments are only to the saturation sliders, and only for the red, orange, and yellow channels, where fall foliage colors occur, plus adjustment to the green channel to smooth color transitions. Avoid excessive green increases to keep the image believable. If your foliage was shot at a long distance, especially through humid air, then global increases to saturation, contrast, and sharpness may be needed to compensate for atmospheric perspective effects.

SpyderCheckr Adjustments, on left, added Visual Adjustments, right


Below is the resulting image. It has been converted to sRGB for the web, so not all colors desired for inkjet output can be included in the images shown here. But the general result of correcting dynamic range, whitepoint, camera color, and foliage fluorescence, instead of simply increasing the saturation slider show even in the sRGB version of the image. In order to print this image, I would now move on to using Lightroom 4’s softproof function, to work with the capabilities of my printer, ink, and media combination as described by my SpyderPrint output profile for the combination.

Image with Visual Tweaks to R,O,Y, G Saturation Sliders

Credits: C. David Tobie, Copyright 2012. Website: CDTobie.com Return to Blog’s Main Page

Thoughts on the Color Gamut of the iPhone 5

In announcing the new iPhone 5, Apple has confirmed that they are extending their recent color strategy. This strategy is to bring all of their devices, not just to Retina resolution, but to sRGB color standards. For the iPhone 5, as for the new iPad, this is a significant increase in color gamut. For the MacBook Pro, it was actually a reduction of gamut from the most recent previous MacBook Pro. But the value of this isn’t just increased color gamut size; its consistency between devices, and consistency between these devices and the web standard of sRGB. This simplifies color management for most users, by creating close to a one-to-one relationship between the image color space, and the device color space.

With the release of the new iPad, and the Retina MacBook Pro, Apple did not use the term “sRGB” when describing their color. But at the iPhone 5 event, they chose to actually use the term sRGB. So its now an official standard, not just an observation by outside experts like myself: Apple is moving its devices to an sRGB standard. There will be complaints that this is not large enough, that AdobeRGB is the ideal color gamut for displays, which may be true for some advanced photographic uses; but for most users, and especially for mobile devices accessing the web, sRGB is the best choice. Custom calibration can still offer improvement on these devices, but their general color representation is quite good for sRGB files, given their sRGB device space.

Retina Gamut compared to sRGB

Earlier Apple Device Gamut


Credits: C. David Tobie, Copyright 2012. Website: CDTobie.com Return to Blog’s Main Page

New-Generation Color Calibrators and Display Gamut Concerns

The latest generation of display calibration products from the major manufacturers use a library of display models to allow them to make more accurate measurements of the gamut of various display types. While this technique increases display calibration accuracy, it can also cause concern amongst users who upgrade from earlier models, only to find that the gamut graph using the new calibrator appears to provide them with a smaller gamut than they were achieving with their older calibrator.

Blue: Older Calibrator. Red: Newer Calibrator

The graph above illustrates this phenomenon. At first glance it would be easy to wonder whether you were somehow “losing gamut” with your newer calibration device.

The reality of the situation is quite different. Both the older and newer calibrators may produce nearly identical results on easy-to-read screen types, but on wide gamut displays or more difficult-to-measure screen types, the newer model is likely to produce more accurate results. These improved results most often mean a reduction in the measure of saturation of the display primaries, especially the green primary, and to a lesser extent the red primary.

This means that the “smaller” gamut being seen when comparing the gamuts of the older and newer display profiles actually indicates a more accurate measurement of the screen. In addition, defining the primaries as less-saturated has the counter-intuitive result of showing colors as more saturated on screen, instead of less.

So if comparisons between your older and newer display calibration tools produces this type of result, rest assured that you are not “losing gamut” but in fact getting both more saturated, and more accurate, color with the newer product.

Credits: C. David Tobie, Copyright 2012. Website: CDTobie.com Return to Blog’s Main Page

Analysis of the Samsung Galaxy Tab 2 Screen’s Color Gamut

Samsung Galaxy Tab 2 Gamut vs sRGB

The illustration above shows the color gamut of the seven inch Samsung Galaxy Tab 2, compared to sRGB. This gamut looks quite familiar to anyone who has analyzed the gamut of laptop computers and tablets over the last few years. It can best be described as “small and twisted.” This refers to the fact that the corners of its gamut triangle are not as far from the center of the triangle as the sRGB corners (called primaries), and as well as the fact that the corners are not aligned with the sRGB primaries. The result of this is that colors tend to be the wrong hue when viewed on such as device, and that colors on the device will be undersaturated as well.

Many laptops have similarly small and twisted gamuts. Apple MacBooks had such a gamut until the quite recently. And iPads had such a gamut as well, in the first and second generation iPads. However the iPad 3 moved to a gamut very close to sRGB; as did the Retina display MacBook Pro (see assorted articles on this blog describing these devices).

Gamuts don’t always increase over time: the most recent pre-Retina MacBooks had a gamut somewhat larger than sRGB; normalizing the Retina MBP gamut actually involved reducing the gamut. Similarly the gamut of the first Samsung Galaxy Tab was a bit larger than the gamut of the v2 device, though still sub-sRGB, and still twisted.

The illustration below shows the gamut of the iPad 1 or 2 (they contained the same screen and had the same gamut), which careful comparison will show to be a bit larger than the Galaxy Tab 2, as well as less twisted. But the iPad 3 screen is more interesting, being nearly a perfect sRGB gamut size.

iPad2 gamut over iPad3 gamut

There are multiple advantages to a gamut closely replicating sRGB. It means that even non-color managed applications will show sRGB images correctly, including most web images, where sRGB is the standard, and much video, where the color definitions are similar to sRGB. It also means that variation between various devices, such as your iPad 3, and your MacBook Pro, will be minimized as well.

sRGB gamut over iPad3 gamut

So while Android tablets may be making progress in some areas, its clear that the color gamut of even the flagship devices is not yet up to the standards of the latest iPads. The next tablet of interest to measure will be the Google Nexus; and following that, the Microsoft Surface tablet. When these devices become available, I will attempt to publish articles covering them. The varying, sub-sRGB gamuts of Android tablets means that calibration of these devices will be required to produce consistent and accurate color on them. Datacolor plans to produce an Android version of SpyderGallery, which would help considerably with this issue.

Credits: C. David Tobie, Copyright 2012.   Website: CDTobie.com   Return to Blog’s Main Page