[Scribus] Image resolution

[jon]

Am 01.05.2007 um 02:43 schrieb ols6000 at sbcglobal.net:

> At 05:25 PM 4/30/2007, you wrote:
>>> An example image is 6495 x 3952 pixels, 4800 dpi.
>>
>> That DPI is WAY higher than is practical. I would suggest scaling  
>> the images down quite a bit.
>
> Well, let's say I'm using a 1200 dpi printer. If the image is to be  
> printed at a size of 5" x 3", then I am printing 6000 x 3600  
> pixels. Seems about right to me.


If you are using a printer with standard raster output, the finest  
point size you can achieve with 1200 ppi
(full color resolution 16/16 point matrix, 256 raster dot sizes,  
about 0.4% - 100% (stepsize about 0.4%
- not all dot positions are possible for all screenangles)
is about 75 lpi (lines per inch <= 1200/16).

On Inkjet it's only "virtually" 75 lpi because Inkjets are scattering  
and use variant techniques to enhance the output.
Virtually most Inkjets are fine with about 200 to a max of 600 dpi  
for color output ?

A standard rule for preparing color image resolution for professional  
output is to use an ideal scale of 2 regarding the output raster  
resolution.
For 152 lpi => 304 dpi (amplitude or frequency modulated screening or  
not)
or if not available a scale of 1,414 (square root of 2) or 1
At least one have to make sure the downscaled dpi (if not 1:1) is an  
integer

Monochromatic images (only bitmap) can be prepared with 1/2 or full  
resolution of the image setter
Greyscale mono- or duochromatic images does not need different  
settings than full color images.
Sometimes, depending on the kind of image setter better results may  
be achieved with doubling the standard resolution (152 lpi => 608 dpi)

Through most of the tests we made with full color images using higher  
OR lower resolution than the double of the raster resolution results  
in visible degrading of results when printed.

???
I don't know how scribus scales images. But an image with 6495x3952 p  
and a resolution of 4800 dpi results in an image of approx. 1.4'' x  
0.8''.
To achieve a size of 5'' x 3'' you have to scale it approx. 300%. IF,  
what I don't know, scribus "really" scales the image, this might  
increase the memory consumption
by factor 9 up to 660 MB (((6495*3952*8)/8)*3)*9 per image
???
If the above does or does not apply,
I think you can scale your images down to at least 600 dpi. This  
might save you about 60 MB per image (5'' x 3''/600dpi=>15,4MB;   
1,4'' x 0,8''/4800dpi => 73,8MB).
May be not :), depends on the kind of output device and processing  
you use.
Jon