Sam North
16th of April 2004 (Fri), 02:02
If you’re into digital B&W, this information may be of interest to you.
Separating channels to red, green and blue produces results remarkably like coloured filters with black and white film. I use this software process from time to time when I’m creating B&W shots – I no longer use B&W film.
But now, with my DSLR, I noticed the image quality can appear a little blotchy at times especially, it seems, if the exposure is fairly lengthy. This never seemed to be a problem with my Reala film.
Just yesterday I read a not-so-interesting article on interpolation in the UK magazine Digital Photographer. A side panel on the page is interesting however, and helps to explain why I was seeing a slight degradation in some images:
INTERPOLATION AS STANDARD
If you use a digital camera there’s no escape from interpolation. With the exception of Sigma’s SD9 and SD10 models, which use Foveon’s three-layer imaging chip, all cameras use a single-layer CCD or CMOS chip.
In order for the sensor to record colour information rather than simple light intensity, the individual photosites are overlaid with an RGB colour filter, usually in what’s called a Bayer pattern. Therefore, each photosite can only detect red, green or blue, depending on the colour of its filter. (To be precise, one photosite in four is red-sensitive, one in four is blue-sensitive and two in four are green-sensitive – the human eye apparently responds better to image detail in the green area of the spectrum.)
In fact, all the red information in a 6-megapixel digital camera image has had to be interpolated, in-camera, from just 1.5 million red pixels. The same applies to blue information. Green data comes from 3 million pixels. This is one reason whey the individual colour channels in digital camera images often appear blotchy and unsharp, and why it’s often not possible to manipulate them as heavily as you can a film scan.
Separating channels to red, green and blue produces results remarkably like coloured filters with black and white film. I use this software process from time to time when I’m creating B&W shots – I no longer use B&W film.
But now, with my DSLR, I noticed the image quality can appear a little blotchy at times especially, it seems, if the exposure is fairly lengthy. This never seemed to be a problem with my Reala film.
Just yesterday I read a not-so-interesting article on interpolation in the UK magazine Digital Photographer. A side panel on the page is interesting however, and helps to explain why I was seeing a slight degradation in some images:
INTERPOLATION AS STANDARD
If you use a digital camera there’s no escape from interpolation. With the exception of Sigma’s SD9 and SD10 models, which use Foveon’s three-layer imaging chip, all cameras use a single-layer CCD or CMOS chip.
In order for the sensor to record colour information rather than simple light intensity, the individual photosites are overlaid with an RGB colour filter, usually in what’s called a Bayer pattern. Therefore, each photosite can only detect red, green or blue, depending on the colour of its filter. (To be precise, one photosite in four is red-sensitive, one in four is blue-sensitive and two in four are green-sensitive – the human eye apparently responds better to image detail in the green area of the spectrum.)
In fact, all the red information in a 6-megapixel digital camera image has had to be interpolated, in-camera, from just 1.5 million red pixels. The same applies to blue information. Green data comes from 3 million pixels. This is one reason whey the individual colour channels in digital camera images often appear blotchy and unsharp, and why it’s often not possible to manipulate them as heavily as you can a film scan.