Pixel:
The basic unit of digital sampling. A dot.
Consists of either:
- bitmap: black or white 0 or 1 - "on" or "off"
- one channel : up to 256 levels of grey
- three channels :red, green, blue [fourth channel: masking, etc]
- four channels: defining colors for printing to paper.
ppi:
PIXELS PER INCH - where pixels actually get a real dimension.
Resolution
How many Pixels per inch there are - on a physical surface, not as abstract pixels in a file.....
Image Size
You mean in dimensions on a paper?
Right. That's it?
Sharpness:
Sharpness is a cheap trick to make up for the fact that all digital images are blurry. The photo processor does a number of tricks with the samples to make them define [yet smooth] edges and make surfaces smooth.
Applying Sharpness is only valid once you know the final output size and printing method. It is a way to decide what edges are and increase contrast in pixels adjacent to this edge. When printed, the edges will stand out instead of blurring back into the background.
Sharpening is a non-intuitive activity. This why I recommend an expensive tool called "Nik Sharpener Pro" [promotional consideration given] that will automatically sharpen an image for any given output situation. Once you have seen Nik operate however, you can apply similar effects with Photoshop's "Unsharp Mask" tool.
It is non-intuitive because when sharpening for paper, images look poor on screen - "videoed." When printed however, they look crisp.
The irony is that many ArchiCAD users think that they can compensate for blurriness by making more pixels. Once you've exceeded the limit of your printer - that's it. Edges need to be "sharpened," not pixels added.
Megabit of file:
This refers the the ultimate ability of the file to record color changes:
1 bit - B+W
8 bit -a file with 256 levels for each color - the traditional 16 million colors.
16bit - the next stage of subtlety with many more levels for each channels - able to represent a broader range of dark to light - common in professionnal photography. You'll see this more in coming years as displays get brighter [able to actually represent the increased subtlety] and in HDRI renderings.
Or did you mean Megabyte?:
MEGAPIXEL of camers:
How many pixels the camera makes. See:
www.dpreview.com for actual pixel sizes of images for any given camera.
dpi:
DOTS PER INCH: the number of color dots an inkjet printer can make from each color jet is 360. When you have four color jets, they individually put out 360 dots per inch. So that is always the absolute mechanical resolution of an inkjet printer.
But then "they" got clever. If you watch an inkjet printer work, you'll see how the colors are printed with many printhead passes where color squirts accumulate to form a vibrant image. The 360 dpi jets "dither" their two "picolitre" squirts of ink into a smooth image. This is how they can claim 2880 and other absurd "resolutions."
Abstract painters like Jackson Pollock used more paint than that. When drunk Jackson was splattering his paint [seed] on those canvasses, industry experts were calling them bassolitres.
The relationship of these things are simple mathematical expressions - it is confusing because the computer display is good at disguising how coarse an image is while paper does not lie. We are often disappointed by the printed result because it looked so good on the screen yet is only a thumbnail on the page.
Try exercises on grid paper if you can't easily visualize this....
Dwight Atkinson
