Placing 300 dpi images at more than 100% 2

[mazzystar]

Hey All,

Two projects: same issue: slight differences.

First project is a 4 x 9 rack card that is going to be offset printed at a gang run print shop. Not highend printing to begin with however... The image on the front is a bit too low res for what I'd like to use it for. Question is, how much can I technically blow it up beyond 100% without it looking like total garbage. Right now it's at 130%. It's an image I purchased from Getty so it's not a snapshot quality image.


Second project is a booklet, 11 x 17 pages folded to 8.5 x 11. This is going to be digitally output on a Xerox Docutech machine but there may be other documents in the series using the same graphics that I will be having offset printed at a later date. I'd like to bump the size of the images up to 150% to accommodate my design. One image was taken by a digital camera, the other was a flatbed scan from a photo. Both are nice professional looking pics. Not crummy snapshots.

a) Will 150% be just too big to maintain quality on a digital machine and/or on an offset press and;

b) Is there a greater chance of the digital pic coming out looking worse than the flatbed scanned image.

Thanks in advance for any help you can give me!

 

[tperkins]

Firstly for a quality looking reproduction of a press, digital or offset, the image really needs to be 300 dpi at 100%. So if you have a picture that you want to enlarge 130% your image dpi needs to be 390dpi. And if you want to enlarge your picture 150% your image dpi needs to be 450dpi.

What are the images in question dpi?

Tony Perkins

 

[RyanPace]

You can get a lot of different answers here. It depends on the equipment specs you will be using. Most presses run anywhere from 133-175 line screen, equivalent to 266-350 dpi. We have had acceptable results on our presses running lower resolution. Usually below 250dpi you will start to notice pixels. It all depends on what is acceptable to you. As TPerkins said above it is all proportional. 300 dpi image placed at 200% is really a 150 dpi image. 300dpi place at 100 percent is standard.
Your Xerox job should be fine, but if you will be printing some of these pieces later you may want to plan ahead and get proper image sizes.

 

[mazzystar]

Tony and Ryan,

Thanks for your feedback. Ryan, as you say, there are many answers to this question. I just spoke to a designer who has been in the business for about a decade and he tells me that he wouldn't place an image that was less than 200 dpi.

After swapping pixels for increased image size, he says you can follow up with these steps in Photoshop to remove some of the graininess of the image.

- Convert the Image Mode from CMYK to Lab Colour

- In the Channels Palette add a slight Gaussian blur to Channel A and then do the same for Channel B.

- Convert the Image Mode back to CMYK.

 

[dabob]

just thought I would throw in my 2 cents worth . . .

the best rule of thumb for images and resolution that I have found and tested is that the effective image resolution needs to be 1.5 x the desired screen ruling . . . .

i.e. to print at 150 lpi the effective resolution required would be 225 dpi and for a 200 line screen it would be 300 dpi

also there is a plug in for photoshop that lets you up-rez photos with very good results (to a point) called genuine fractals from lizardtech software that I have used with surprising results the url is :

http://www.lizardtech.com/

good luck . . .