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Pre-Visualization Strategies for Piezography intro

by
Jon Cone
published on 01/20/2009 19:00:00

Standard K7 profiles are made to differentiate between 256 gray levels from RGB value 0 (black) to RGB value 255 (white). Therefore, displays should be calibrated to print specs of an approximate contrast ratio of 275%, with black point near .34 cd/m2 and a white point near 90 cd/m2. These Luminance values are not very dark, nor very bright and are intended to make the display imitate ink on paper. In fact, the appearance of a properly calibrated display can be quite unusual when the user realizes that their uncalibrated display has a native contrast ratio often as bright as 875%. And admittedly a display with a contrast ratio of 875:1 is quite amazing to look at one’s photographs on. A contrast ratio of 400:1 is amazing! So when asked to calibrate a bright display to imitate the relative reflectance ratio between paper white and ink black, the average photographer rebels! But, without reducing the display to print calibration, the photographer can not “see” what Piezography can print. 

A display with too large a contrast ratio necessarily compresses the shadow detail. The image on screen looks dark, rich with very deep shadows. However, Piezography is not like Epson ABW K3 which naturally compresses shadow detail. Piezography K7 profiles is a true linear system – perhaps the first and only in the history of Photography. The only true black which Piezography prints is a pixel value of 0 (from 0-255). So if you can’t see how RGB values of 2,3,4,5,etc are becoming lighter and lighter – then your first print with the system may seem “too light” and without any blacks…  and worse, you may not be getting the best out of Piezography.

Calibrated versus Un-Calibrated

Calibrated versus Un-Calibrated

The above graphic is a representation of a print calibrated display and a display calibrated improperly. The upper band of gray values is clearly linearized from black to white. On the display which is not calibrated, there is an impression of a much darker image as represented in the lower band of gray values.

Standard K7 profiles are made to differentiate between 256 gray levels from RGB value 0 (black) to RGB value 255 (white). Therefore, displays should be calibrated to print specs of an approximate contrast ratio of 275%, with black point near .34 cd/m2 and a white point near 90 cd/m2. These Luminance values are not very dark, nor very bright and are intended to make the display imitate ink on paper.

It is highly possible that if you are reading this blog on a display which is not calibrated that you may have trouble discerning the differences in the  two bands of gray patches. But they have been altered to give some separation even on a display which is not calibrated. In fact the following graphic represents RGB values from Black (0) to a dark gray (63). On a calibrated display for print, you should just be able to make out 2,3,4 or 5. If you can’t – you’re simply calibrated too bright.

RBG values 0 - 63

RBG values 0 – 63

When it comes time to look at an image on a monitor. What assumptions are you making? The quality of your calibration determines the shadow separation which you can see. The image should print just like it displays, and will if you are calibrated. But, what happens when you see a dark gray as black as depicted in the following graphic?

Is it really black? No its a dark gray...

Is it really black? No its a dark gray…

What happens is that the “black” which looks “black” actually prints as a dark gray because it really is a dark gray. Take a look at the following graphic. Because the histogram of this image file reveals that this image actually does not contain any “black” at all – even if it “looks” black on an improperly calibrated display.

raw-histogram49 pixels of RGB value 9 represent the darkest gray in the image. There are zero black pixels (RGB value 0). The majority of the dark tones in this image file are actually in the 3/4 tone zone. There should be no expectation that this image will print a decent black. By the way, there are also no pure white pixels – but photographers seldom which to push the highlights as they do the shadows. Yet, Piezography is unique in printing magnificent highlight separation and detail.
In the next entry (Pre-Visualization Strategies for Piezography part 2)I will illustrate why displays can fool the eye, and an alternative workflow.