Adobe Photoshop CS5 for Photographers - Martin Evening [90]
Where you should set the highlight clipping point is really dependent on the nature of the image. In most cases you can adjust the Exposure and Recovery sliders so that the highlights just begin to clip and not worry about losing any important highlight detail. If the picture you are editing contains a lot of delicate highlight information then you will want to be careful when setting the highlights so that the brightest whites in the photo are not too close to the point where the highlights get clipped. The reason for this is all down to what happens when you ultimately send a photo to a desktop printer or convert an image to CMYK and send it to the press to be printed. Most photo inkjet printers are quite good at reproducing highlight detail at the top end of the print scale, but at some point you will find that the highest pixel values do not equate to a printable tone on paper. Basically, the printer may not be able to produce a dot that is light enough to print successfully. Some inkjet printers use light colored inks such as a light gray, light magenta and light cyan to complement the regular black, gray, cyan, magenta, yellow ink set and these printers are better at reproducing feint highlight detail. CMYK press printing is a whole other matter. Printing presses will vary, of course, but there is a similar problem where a halftone dot may be too small for any ink to adhere to the paper.
In each of the above cases there is an upper threshold limit where the highlight values won't print. So, when you are adjusting the Exposure and Recovery sliders, it is important to examine the image and ask yourself if the highlight detail matters or not. Some pictures may contain subtle highlight detail (such as in Figure 3.31 ), where it is essential to make sure the important highlight tones don't get clipped. Other images may look like the example in Figure 3.32 . Here, the light reflecting off a shiny metal surface creates bright, specular highlights and the last thing you need to concern yourself with is preserving the highlight detail. I would say that most images contain at least a few specular highlights and it is only where you have a photo like the one shown below that you have to pay particular attention to making sure the brightest highlights don't get clipped.
Figure 3.31 In this example it was important to preserve the delicate highlight tones in the fish steaks. To be absolutely sure that I didn't risk making the highlight detail areas too bright, I placed a color sampler (circled) over an area that contained important highlight detail. This allowed me to check that the RGB highlight value did not go too high. In this case I knew that with a pixel reading of 229,229,228, the highlight tones in this part of the picture would print fine using almost any print device.
When to clip the highlights
As I say, you have to be careful when judging where to set the highlight point. If you clip too much then you risk losing important highlight detail. However, what if the image contains bright specular highlights, such as highlight reflections on shiny metal objects? The Figure 3.32 image has specular highlights which contain no detail. It is therefore safe to clip these highlights, because if you were to clip them too conservatively you would end up with dull highlights in your prints. In this case the aim is for the shiny reflections to print to paper white. So when adjusting the Exposure slider for a subject like this, you would use the Exposure slider first to visually decide how bright to make the photo and not be afraid to let the specular highlights blow out to white.
Figure 3.32 The highlights in this photograph contain no detail, so there is no point in trying to preserve detail in the shiny areas as this would needlessly limit the contrast. One can safely afford to clip the highlights