• Choose a category
• All
• Classic-Fiction

By Root 1699 0

print. As a result of this, in the early days of digital imaging, the only way to get a digital image to print correctly was to manually adjust the output levels so that the black clipping point matched the print device. Back then, if you set the levels to 0,0,0, RGB, the blacks would print too dark and you would lose detail in the shadows. Therefore the solution was to set the output levels point to a value higher than this (such as 20,20,20 RGB), so that the blacks in the image matched the blackest black for the print device. These are the historical reasons for such advice, because the black levels had to be adjusted differently for each type of print output including CMYK prepress files.

For the last 12 years or so, Photoshop has had a built-in automated color management system that is designed to take care of the black clipping at the print stage. The advice these days is therefore quite simple: you decide where you want the blackest blacks to be in the picture and clip them to 0,0,0, RGB (as discussed on the previous page). When you save the image out to Photoshop as a pixel image and send the image data to the printer, the Photoshop or print driver software automatically calculates the precise amount of black clipping adjustment that is required for each and every print/paper combination. In the Figure 3.34 example you can see how the black clipping point for different print papers is automatically compensated when converting the data from the edited image to the profile space for the printing paper. Don't just take my word, it is easy to prove this for yourself. Open an image (almost any will do), set the Channel display in the Histogram panel to Luminosity and refresh the histogram to show the most up-to-date histogram view (you do this by clicking on the yellow warning triangle in the top right corner). Once you have done this go to the Edit menu, choose ‘Convert to Profile’ and select a CMYK or RGB print space. You'll need to refresh the histogram display again, but once you have done so you can compare the before and after histograms and check what happens to the black clipping point.

Figure 3.34 The Histogram panel views on the right show (top) the original histogram for this ProPhoto RGB image. The middle histogram shows a comparison of the image histogram after converting the ProPhoto RGB data to a print profile space for Innova Fibraprint glossy paper printed to an Epson 4800 printer. The print output histogram is overlaid here in green and you can see how the black clipping point has been automatically indented. The bottom example shows the print profile for a Somerset Velvet matte paper printed to an Epson 9600 printer, again colored green so that you can compare it more easily with the before Histogram. The black clipping point is moved inwards even more here because the matte paper needs a higher black clipping point to avoid clogging up the shadow detail. The same thing also happens when you make a CMYK conversion, but the black point will possibly shift inwards even further. Please note that the histograms shown here were all captured using the Luminosity mode since this mode accurately portrays the composite luminance levels in each version of the image.

Digital exposure

Compared with film, shooting with a digital camera requires a whole new approach to determining what the optimum exposure should be. With film you tended to underexpose slightly for chrome emulsions (because you didn't want to risk blowing out the highlights). With negative emulsion film it was considered safer to over-expose as this would ensure you captured more shadow detail and thereby recorded a greater subject tonal range.

When capturing raw images on a digital camera it is best to overexpose as much as it is safe to do so before you clip the highlights. Most digital cameras such as digital SLRs and even the raw-enabled compacts are capable of capturing 12 bits of data, which is equivalent to 4096 recordable levels per color channel. As you halve the amount of light that falls on the chip sensor, you potentially halve