Hi,
udi.kor@gmail.com (2006-03-19 at 2348.25 +0200):

what is the difference between resoloution and size? between a picture with height:100; width:100 and resolution:200 to height:100; width:100 and resolution:400 ? Udi

Resolution is a hint for the real world print size and size is the pixels you really have (assuming you are displaying width and height in pixel units). So both have the same number of pixels, but one is declared to be printed as 0.5 inch side square and the other as 0.25. Some people get really picky about the resolution being correct so they know the print size without doing maths, and others think that changing the number will do magic and give you a non pixelated print.

GSR

Hi,
anti@mad.hu (2006-03-19 at 2339.24 +0100):

Hi!

... and is there any difference in picture if I set:

100x100 in 400dpi or
200x200 in 100dpi

and make a print from it (in same size - 10cm x 10cm for example)?

Then it is not 400 or 100 DPI, but (rounding to 1 inch = 2.5 cm) a 4 inch print, so you have printed 100 pixels to 4 inches and 200 to 4 inches too, so that was 25 and 50 DPI. Maybe you are confused with the printer's DPI (300, 720, 1440...) but those are not pixels, but ink dots. The print system has to convert the file/screen pixels (think about them like squares or rectangles with different levels of intensity) to ink dots which are on or off (one level of intensity, so the printer creates patterns of dots to simulate the intensity levels when looked from "far away").

Thanks:
Anti

On Sun, 2006-03-19 at 23:10 +0100, GSR - FR wrote:

Hi,
udi.kor@gmail.com (2006-03-19 at 2348.25 +0200):

what is the difference between resoloution and size? between a picture with height:100; width:100 and resolution:200 to height:100; width:100 and resolution:400 ? Udi

Resolution is a hint for the real world print size and size is the pixels you really have (assuming you are displaying width and height in pixel units). So both have the same number of pixels, but one is declared to be printed as 0.5 inch side square and the other as 0.25. Some people get really picky about the resolution being correct so they know the print size without doing maths, and others think that changing the number will do magic and give you a non pixelated print.

GSR

GSR

GSR - FR wrote:

Hi,
anti@mad.hu (2006-03-19 at 2339.24 +0100):

Hi!

... and is there any difference in picture if I set:

100x100 in 400dpi or
200x200 in 100dpi

and make a print from it (in same size - 10cm x 10cm for example)?

Then it is not 400 or 100 DPI, but (rounding to 1 inch = 2.5 cm) a 4 inch print, so you have printed 100 pixels to 4 inches and 200 to 4 inches too, so that was 25 and 50 DPI. Maybe you are confused with the printer's DPI (300, 720, 1440...) but those are not pixels, but ink dots. The print system has to convert the file/screen pixels (think about them like squares or rectangles with different levels of intensity) to ink dots which are on or off (one level of intensity, so the printer creates patterns of dots to simulate the intensity levels when looked from "far away").

I have been trying to understand this better myself. I couldn't find any good
help on it. My goal was to determine the maximum size image in pixels that would
print exactly on a letter-size paper with no scaling. I built a resolution test image
and found that the highest resolution that I could see a 1 pixel line on my printer
was about 150 pixel/inch. This is on windows xp. I see that in at least some file
formats, the resolution setting is saved in the metadata as dpi. But when I print the
image using different applications, I get different results. The apps seem to use or
package the data differently for the driver. For example, one app has options in
the print dialog for "fit pixels" "fit resolution" and "fit to page". I haven't figured out
yet exactly what this does (other than fit to page obviously scales the data up or down
as required.

My printer also has a poster mode (2x2, 3x3,4x4). As best I can determine all this does is first scale the image to a single page in the app and then the printer just zooms it (I don't know if it does any sort ot interpolation but I doubt it).

scott s. .

On Monday, March 20, 2006 12:02 PM [GMT+1=CET], scott s. wrote:

[..]

I have been trying to understand this better myself. I couldn't find any good help on it.

Although it focuses on scanning, this has an explantion of pixels, dpi, images, printing, etc.:
http://www.scantips.com/basics01.html