Talk:Photo-quality printing

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Hmmmm. A few issues/questions about this article...

In describing why photo-quality printing requires images in excess of 1200ppi, the article states:

"Photo quality printing requires images to contain the most amount of color information possible."

Later on it notes that Photo-quality output yields:

"... truer color values and hues due to the greater amount of color information stored in the high resolution image or artwork file."

The former is inexact or misleading at best, the latter is straight-up mistaken. Resolution (in pixels per inch) is not about the amount (or lack) of "color information" in an image, but rather of the density of spatial image data. The relative amount of color data in an image is reflected rather in (a) the measurement of color depth (in bits per pixel, or bits per pixel per channel) and (b) the range covered by the image's color gamut.

We also read:

"The high resolution images used in photo quality printing is saved in a CMYK file format to best utilize either the commercial printing process or inkjet printing photo quality output capabilities."

CMYK color is certainly necessary for commercial offset printing but, as far as I know, this simply doesn't apply to inkjets. Even high-end, large format inkjets sporting 8 separate inks are generally RGB devices (and they certainly don't require 8 color separations). Converting an image to CMYK for printing to these is pointless, as it will just be converted back to RGB on the fly anyways (with a possible loss in color data if colors in the original fall outside of the CMYK gamut, depending on the conversion).

Finally, there's this about lpi:

"The high resolution photos are printed (or output) at a line screen value of 1200 lines per inch."

Like CMYK, line screen frequency is an important thing with offset process printing, but not so much with inkjets. Whereas the traditional halftone screening often used in printing presses employs amplitude modulation (varying the ink density by varying the sizes of dots against a consistent line screen frequency), inkjets almost universally utilize stochastic screening that is frequency-modulated (varying the ink density by varying the frequency of consistently sized dots).

Stochastic screening can also be used in press printing (and, as it offers a closer approximation to a continuous tone image than traditional halftone screening, I would not be surprised at all if it sees use in the application in question).

Following immediately from this, also in regards to lpi:

"Traditional full color printing is done at a line screen ranging from 300 to 600 lpi."

This is simply not true. Traditionally, newspaper photos have been printed at a line screen of 85 lpi, most magazines and books at 133 lpi, high quality brochures at 150 lpi, and art-quality books topping out at 175 lpi or higher. Direct to plate technology does allow for yet higher line frequencies, but this 300 to 600 lpi figure for "traditional full color printing" is patently false.

This figure is so off the mark, in fact, it renders suspect the aforementioned 1200 lpi screen that is said to be used for photo-quality printing (and I have been unable to verify this 1200 lpi figure via Google).

Is the "PrintingPro" who wrote this article anything of the sort?

76.197.210.51 18:14, 22 March 2007 (UTC)