output resolution selection
PostPosted: Sun Oct 03, 2004 6:54 pm
by pmitterboeck
what's the reason for the way SilverFast is calculating the output resolution of an image? I don't understand the difference between selecting the resolution the image should have at the end (i.e. 450 dpi) setting the quality factor to 1 and the grid width to 450 lpi or - at the other hand - setting the quality factor to 1.5 and the grid to 300 lpi.
Thank you for explanations!!!!
PostPosted: Mon Oct 04, 2004 1:31 pm
by LSI_Noack
Dear pmitterboeck
seems to me that the is no difference in input, but in output resolution, i.e. you shall in case (a) receive an image with is set to 450 dpi and in (b) to 300 dpi.
lpi vs dpi; ie, offset printing vs digital
PostPosted: Mon Oct 04, 2004 2:48 pm
by Gregory C
if you are scanning and processing an image to be printed in an offset printer, you can have SF calculate the optimal output resolution for you.
1. enter the output height and width; ie, the dimentions of the image as they will appear in the printed article. you can ignore the original dimensions and the scale factor fields.
2. enter the offset printer's lines-per-inch. it could be anything from 85 to 175 or even higher depending on the quality of the magazine.
3. enter a Q Factor. apparently (and I'm no expert), 1 / pi is the optimum, or approximately 1.4. or if you want to keep things simple, specify 1.5.
SF will automatically calculate the optimum input resolution to produce an image just large enough to print beautifully at the size and screen you specified. if you scanned at a higher resolution, the scan would take longer to complete, the image screen would take much longer to output, and the final printed image would not look significantly better. if you scanned at a lower resolution, the final printed image quality may not be acceptable.
if you are scanning for web display or inkjet printers where you know the required output resolution (72 or 100 for web display, and approx 225 to 400 for inkjet printers), specify the output dimensions and the input resolution. ignore the screen, Q factor and scale fields.
I have argued that for modern day scanning where many of the output images are destined for digital media, the fields should be more pixel-centric and the input resolution and output resolution values should be both visible. maybe something in this respect will happen in a future update.
regards
Gregory