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About Slide Scanning Contrast

Why is slide scanning contrast such an important factor for scanned slide or image quality? We distinguish objects from each by the differences in contrast or color. Of these two factors, contrast plays the most important role, since your eyes are much more sensitive to contrast. Unfortunately, contrast is very hard to get right when scanning slides. At DpsDave, our unique equipment is able to capture the contrast when we scan your slides!

Before we continue, we do want do differentiate contrast from dynamic range and exposure. Dynamic range is contrast in the scene. Exposure is how bright a scene is overall. Illumination level and contrast will not be same for photo and the real scene.

To learn more about slide scanning contrast vs. some other terms you might have heard, contact DpsDave today and we will clarify for you!

How Our Eyes Recognize Contrast

Our eyes have two types of light sensing cells, those that are sensitive to how much light there is (rods), and those that can tell what color the light is (cones). The rods outnumber the cones by 20 to 1, making our eyes much more sensitive to how much light there is than to what color. Humans are sensitive to contrast. A ratio of 1:2 is perceived as the same contrast as a ratio 100:200. Illumination has a multiplicative effect.

The sharpness and detail comes from the black-and-white part of our vision. Scientists and artists refer to the part of the image which comes from the black-and-white part of our vision as contrast, and it is perhaps the most important thing for slide scanning service companies to pay attention to when they convert slides to digital.

Have questions that weren’t answered here about how our eyes recognize contrast and their limitations? Give DpsDave a call at 866-935-1361!

Slide Scanning Contrast Taken Into Account as Part of DpsDave Slide Scanning Services The result is as shown to the left. The high contrast scan is from DpsDave, and the low contrast portion is from a slide scanning competitor.

 

About Slide Contrast Quality

In the olden days, newspaper printers found that if they increased the contrast in their illustrations and photographs, their pages (which are really low resolution) looked much better. Television shows are designed with high contrast content for this reason. (You will never see a newscaster in a checkered suit for just this reason!).

Slide scanning contrast is hard to get right. Increasing the brightness wipes out the detail in the shadows. Photographers sometimes adjust the contrast level of their photos to set the feeling of a photograph. Reduce the contrast and you can convey a dreamy or romantic feeling. A slide scanning system must be able to reproduce the contrast of the original slide.

Engineers have defined “contrast” as a measure of the image, and it is the ration of the brightest to darkest spots in the image. The term “dynamic range” is an equipment specification, and is a measure of a scanner’s ability to record the contrast in an image.

Slide scanners that list a dynamic range in their specifications are rare, but most report the number of bits in the A/D converters, and this is related to the dynamic range. Scanners with 16 bits of A/D conversion have a dynamic range of 64,000 to 1. However, since there are no standards for how to determine dynamic range, the numerical rating can be abused.

To Edit Before or After Scanning Slides

DpsDave is fully aware that not all customers are going to be professional photographers. For those who are photography buffs, we want to address an issue that often comes up with high-contrast slides. Digital cameras have less dynamic range than your eye or film. High dynamic range (HDR) software can assist, but be aware of halo and purple fringing that can occur while editing.

Some people try to correct after the fact with Photoshop. There is a Brightness/Contrast command, but it doesn’t always work well. Sure, it may make everything brighter, but then you might also get rid of the deep dark tones that brought out the details in the shadows on a slide image. Many users utilize Levels or Curves to help make adjustments as well as looking at the histogram’s 256 brightness values. If you have the Channel option set to RGB, you can view composite of red, green and blue channels to see if there are any real highlights or shadows in the image.

Sure, these are tools within Photoshop, but it is better just to get really close to the final image contrast using scanner software. That way, you fidget less in post-processing.

To get more tips on preventing slide scanning contrast issues before, during or after slide scanning, give DpsDave a call at 866-935-1361!

Slide Contrast vs. Photo Contrast

Some might wonder why we have a page on slide scanning contrast when we already cover photo contrast. Film offers much greater contrast range than printed photos. Slides can have an extreme density range and can extend black tones nearly two orders of magnitude deeper into the zero pit than photo prints. What this means is that usually a higher quality scanner with a better dynamic range is required for slides than for printed photos.

DpsDave uses a multi scanning technique to overlay different scans of the same slide image in order to average out random noise. Dark areas are shown more cleanly. Although we don’t handle negatives, we think it is important to note some differences between slides and negative color film. Negative color film has much less density than slides and the dark noise appears as highlights instead. That being the case, a less expensive scanner may work for negative color film.

Our goal at DpsDave is always to have top quality scanners, so that we are able to meet the needs of our customers. We want the slide contrast to look just like the contrast in your final digitized images.

To learn more about differences between slide and photo scanning when it comes to contrast, call DpsDave now at 866-935-1361!