On Tue, 2007-11-06 at 13:17 +1030, Tim wrote: > On Tue, 2007-11-06 at 10:53 +0900, John Summerfield wrote: > > The more pixels does translate to better printed images, and my local > > camera vendor assured me 3.2 Mp is good to about A4. Which probably > > translates to marginal to the trained eye. > > I found my 4 meg camera to just about manage an A4 sized print, but only > for distance viewing, and only when the source photo was taken under > good conditions. Close up, you could see JPEG artifacts, and artifacts > from the camera and printer (I use the local photo mini lab for my > prints) that try to sharpen the picture more than it really is. > Unfortunately they nearly all try to crispen pictures, rather than print > pictures as they are, or use a camera which has better native resolution > (that's optical and electronic, in combination), in the first place. > > Nearly all electronic imaging relies on artificially peaking the > resolution. Turn off the detail enhancement, and you think "yuck, it's > very soft," like the old soft filters used on female movie stars, even > on $20,000 cameras. Conversely, for film, back when you could still get > your photos processed optically, and you had a decent camera, even a > moderately priced consumer camera, we had better looking prints (from > the decent labs). > > Granted that enlargements tend to be viewed at a distance, and that does > hide some defects, but some are not viewed that way. Such as family > photos sitting in a frame on the desk. They'll probably not be A4 > sized, but still can be big enough to expose some failings in the > system. Never mind someone who wants to be arty, and do big blowups > that will have people gazing intently at them. > > -- > (This computer runs FC7, my others run FC4, FC5 & FC6, in case that's > important to the thread.) > > Don't send private replies to my address, the mailbox is ignored. > I read messages from the public lists. > Jpeg is a horrible compression algorithm. I have no idea why it was chosen. It is lossy, has artifacts in the result, often smearing the image or showing a fingerprint like Moire pattern (most image processing software has an anti-moire filter specifically tailored for JPEG ) and other artifacts. There are better compression algorithms, but many if not all are proprietary. Somewhere in Europe about 2005, there was a new lossless algorithm similar to LZ in compression size or slightly better, and HP licensed it, but I don't know the name. LZ and GIF are also lossless, but GIF somehow lost the ability to do color from what I understand. The problems endemic with images deal with the representation, and the problem with something called tilt, which is an artifact of the digital image capture method from CCD's. CMOS devices don't exhibit this or at least don't have to because the underlying technology is different. CMOS is becoming the imaging technology of choice, but CCD's will be around for a while. The CCD's also suffer more from blooming, (for those of you with film experience, think of acetate contamination) where intense light will affect the surrounding pixels. CMOS doesn't experience this from the base technology although a poor screen which is the surface that covers the detectors may cause a similar effect from light diffusion. The number of megapixels to replicate 35mm film is dependent on several issues, from the size of the imager, to the depth of field of the lenses, and the formation of the screens, along with the design of the technology. However, for a normal 1/4 to 1/3 inch die, 15MP seems about right. For larger imagers, such as the focal plane imagers for 35mm cameras, somewhat more mp may be required. Cannon's current top model now offers the EOS-1Ds Mark III with 21Mp. For still more resolution, the high end manufacturers like Hasselblad offer large format digital SLR's with larger image sensors and >30Mp right now. Hasselblad's H3D II for example offers a sensor of 48x36 and 39Mp. which yields a 44 nanometer pixel size for capture, and the lenses are standard Hasselblad system lenses, so if you put on a telephoto with a 5 degree field of view (about 1000mm lens), you would get a pixel covering 641 nanodegrees, with a dynamic range of about 108db (film is typically only about 65db). The problem comes in storing and manipulating raw images of this size. However the recent introduction of 8-32Gbyte flash is going to make this technology more palatable. Add the ability to fully seal the camera, which will reduce dust and other problems with long term use, and the writing is on the wall about film. In addition, using encryption, and internet, a professional's images can be anywhere in the world in seconds. Even theaters are starting to join the digital revolution, with fully solid-state projectors. For some examples look up Texas Instruments DMD projectors and chips. There is also a single pixel camera using a dmd device to scan the focused image. For still or slow speed, this would permit really flat images with no pixel difference issues at all, very good for some kinds of scientific studies. Additionally there are highly optimized scientific sensors capable of looking from the very low infrared to the very high ultraviolet regions and beyond that are finding niches in microscopy, biology, satellite, astronomy and other fields of research. Some of these images cannot be captured with any existing film due to sensitivity issues, changes in required focus (look at your camera if you have an slr. See the red mark on the focus barrel? That is for infrared film.) and other issues (like getting the film back from space). Some other sensors offer amplification of the detected image, which is similar to low light image intensifiers with perhaps less capability, but fewer problems and greater reliability. Most of the complaints about digital images are actually a result of the post processing that most consumer cameras do on the image. However, if you have a camera that offers it, try capturing the raw image and bring it into a high quality bit of photo processing software, and check out that result. I think you will be surprised. A full sized 8.5x11 image at 3Mp would give you a pixel size of 7.72microns (7.72e-6 inches) in area. This translates to about 360 linear dpi. At 3' the average human eye can only see 3/1000" errors. at 12" that would be 1/1000" errors, and so this image would be on the edge of what you could see. To get this quality, you must use photo quality jets, ink, paper and your printer must be in tip top condition. I don't know the latest on Laser stuff, but you can look it up. Regards, Les H
