I want to expand a bit upon my last PIE Blog article regarding preparing photographs for offset and digital custom printing. As I had mentioned, I have been helping a new designer prepare photographs for a personal history print book about World War II.
The designer has been sending me the photographs as he has completed them, based on the steps I had suggested in the prior article. About half of the photos have been great. By this I mean that the photos the designer has sent me for approval have included a wide range of grays (this is a black-only World War II print book, so all photos have been converted to grayscale images). In the best of the photos, you can see an indication within the “histogram” (a graph accessible through the “Levels” dialog box) that there are pixels in all tonal levels from white to black. This is indicated by a sweeping “mountain range” (by way of analogy) within the histogram, starting with the pure black pixels and extending to the pure white pixels.
(If you’re working in full color instead of black and white, you will also see this histogram, since this graph actually represents not actual shades of gray but brightness levels, or values from light to dark.)
The lower the humps of the “mountain range,” the fewer the pixels of that particular brightness level. If the humps of the graph are high, this indicates more pixels in a certain area (highlights, for instance, in a high-key photo, or shadows in a low-key photo). If there are gaps in the histogram, this means there are no pixels of that particular value. If there are spikes, that indicates an abrupt shift from one value to another.
Sample Photos from the Designer
Some of the photos the World War II print book designer sent me for review were either flat (gray overall, lacking in contrast), or they had pure white areas that appeared to have been painted onto the photo with white paint (or White-Out, for those who remember typewriters). Other photos had blotchy areas (obvious areas of lighter or darker gray that did not blend into their surroundings).
To teach the designer how to best use Photoshop to correct these problematic images, I had him open the photo itself for visual reference, the “histogram” in “Levels,” and the “Info” palette under the “Windows” menu. I wanted the designer to be able to balance an aesthetic, visual judgment of an image with the technical pixel information in both the histogram and the Info palette.
Ultimately, the picture has to look right, visually and intuitively. That’s the real goal. The Info palette (which shows the actual highlight or shadow value–i.e., an 8 percent printer’s halftone dot in the highlights of someone’s face) and the histogram in the Levels dialog box are merely tools to help judge the quality of a photographic image.
What I Suggested (The Goals)
I asked the designer to look for spikes (pixel values that extended to the top of the histogram) and gaps in the histogram. I said these were less than ideal and that they would show up as posterization (visible stair-stepping of values rather than a gradual blending of white into gray into black).
I also suggested that he consider what was most important in an image. For instance, by darkening a background (one photo had the leaves and trees of a wooded area in the background), he could preserve the detail in the clothing of the people in the foreground. Since the people were more important than the trees, I encouraged him to do this. (Sacrificing the background detail brought out detail in the foreground.)
I also encouraged the designer to darken the light tones in the people’s clothing and faces to preserve detail in these areas in order to give them a sense of depth and solidity. The designer’s first attempts included white faces that lacked the details of the cheekbones, eye sockets, etc. Other photos had subjects in clothing that was almost completely white. By darkening the clothing slightly, the designer could give more of a three-dimensional, sculptural sense to the clothing, making the subjects of the photos look real and less flat.
The Best Photoshop Tools for This Work
I asked the designer to try both “Curves” and “Levels” to adjust the tonal values in the photos. Curves would allow him to isolate areas within an image so he could increase the midtones while maintaining the quarter tones and three-quarter tones.
I asked the designer to pay close attention to the value of pixels, monitoring the grayscale changes in the “Info” palette while observing the effects of these changes on the image itself. I wanted him to make sure there was some tonal information even in the lighter areas, and to avoid making any area completely white.
I also suggested that the designer consider using Photoshop’s “masking tools and techniques” to isolate entire regions within a photo so that they might remain untouched while the designer altered other areas with the Levels or Curves tools.
What You Can Learn from This Designer’s Photos
Photoshop is a comprehensive program about which many thick books have been written. It is very powerful, but it takes a long time to learn. I think you may find that a close study of its tools and techniques will be rewarding and will empower you, greatly benefiting your photo manipulation work. In addition, as questions arise for you, feel free to ask the prepress managers at your custom printing supplier for advice and help.
This entry was posted
on Saturday, January 26th, 2013 at 1:00 pm and is filed under Photos.
You can follow any responses to this entry through the RSS 2.0 feed.
Both comments and pings are currently closed.