Pixel dimensions and print dimensions

[JohnT]

Here's something I don't quite understand yet. When I need something printed by Mpix at a size of 5x7 for example, I send them an image that's 500px X 700px at 250ppi. However, if I use these numbers to print it myself using PS, the projected print size is tiny. I'm assuming their software converts the pixel dimensions into the appropriate print size. Can I get PS to do this, or do I want or need to?

[Steelsun]

It all depends on what you set you "Dots per inch" (dpi) or "pixels per inch" as.

At 250 ppi, which would get a 2" by almost 3" pic, which is small.

For a 5"x7" image at 250ppi, you ned to save your image at 1250 by 1750.

[JohnT]

Originally Posted by Steelsun

It all depends on what you set you "Dots per inch" (dpi) or "pixels per inch" as.

At 250 ppi, which would get a 2" by almost 3" pic, which is small.

For a 5"x7" image at 250ppi, you ned to save your image at 1250 by 1750.

Right. I'm just curious as to how Mpix can get a 5x7 from 500px X 700px, and if I can change something in PS to render the same--if I wanted.

[pippin]

because most of those printers don't actually print at 300 dpi - they're a lightjet system, usually running at around 100ppi.

At least thats what my frontier at work does.

[JohnT]

Originally Posted by pippin

because most of those printers don't actually print at 300 dpi - they're a lightjet system, usually running at around 100ppi.

At least thats what my frontier at work does.

Interesting. Thanks.

[rbalcom]

Originally Posted by JohnT

Here's something I don't quite understand yet. When I need something printed by Mpix at a size of 5x7 for example, I send them an image that's 500px X 700px at 250ppi. However, if I use these numbers to print it myself using PS, the projected print size is tiny. I'm assuming their software converts the pixel dimensions into the appropriate print size. Can I get PS to do this, or do I want or need to?

I'm not sure how you ended up with an image size of 500px x 700px at 250 ppi, but the image size command is how to do what you are asking. It is best to set the ppi to either 300 for HP printers or 240 for Epson printers. I have heard rumors at some of the seminars that Epson unofficially has said that you will get good prints at 150, but if you want to save some ink you just need to experiment with different settings and see how you like the print quality. With the ppi set, make sure that you have the resample image box checked and then enter the size of the print you want. PS will resize the image (px dimensions and file size) to give you the size print you want. As a general rule, use Bicubic smother to increase the size and Bicubic Sharpener to reduce the size. After doing that, when you print you will get the desired size print.

I hope that is what you were asking about.

Dick

[island bound]

Fuji frontiers are printing at 300dpi.
I'm with you - I don't know how they convert and 100dpi up.

[jeffkohn]

Originally Posted by JohnT

Here's something I don't quite understand yet. When I need something printed by Mpix at a size of 5x7 for example, I send them an image that's 500px X 700px at 250ppi. However, if I use these numbers to print it myself using PS, the projected print size is tiny. I'm assuming their software converts the pixel dimensions into the appropriate print size. Can I get PS to do this, or do I want or need to?

Most printers and RIPS will ignore the embedded PPI number in the file, it doesn't really mean much. Photoshop is one of the few exceptions, as it will determine print size based on the ppi rather than letting you specify. The PPI is just a piece of metadata in the file.

In the case of lab prints, if you order a 5x7" print, that's what the printer is going to print regardless of the PPI. If the resolution of your file doesn't match the native resolution of the printer, the file will be interpolated on the fly. So when you send a 500x700 file (which for a 5x7" print is only 100ppi), the Frontier is going to interpolate that up to 1500x2100 (assuming printer's native resolution is 300ppi which is true for most Frontiers).

The upshot of all this is that you're probably not getting the best prints you can by sending 100ppi files to the lab. You may think they look good, but if you did a side-by-side comparison against a print from a higher-resolution file I bet you would notice the difference. You don't necessarily have to interpolate up to 300ppi if the source image isn't high enough resolution for that natively, but I wouldn't recommend down-rezzing.

To crop in photoshop, set the crop dimensions to 5in x 7in and leave the resolution field blank. That way cropping won't resize the image. Then, just send the cropped image to the lab without interpolation and you should get good results (if printing really large there can be an advantage to up-rezzing, but that's probably another thread).

If you want to print at home without having to worry about the PPI field, then I would suggest checking out QImage as it make printing pretty easy.

[jeffkohn]

because most of those printers don't actually print at 300 dpi - they're a lightjet system, usually running at around 100ppi.

Sorry but that's just not true. They may be able to accept files at 100ppi and make prints, but that is not the native resolution they're "running at". They're probably running at 300ppi or 320ppi depending on if it's a Fuji or Noritsu (and there may even be a few models that run even higher). When you feed these printers a 100ppi file, they interpolate it.

[JohnT]

Thanks for all the info, folks. What caused me to ask the question in the first place is that the 4x6 prints that I'm getting from Mpix are not the quality that I'd like. They're "ok", but could be better I think. In fact, comparing them to some film 4x6 prints that I have, the digital ones are lacking. They look digital if that makes any sense. I ordered test prints three times, each batch having been processed and sharpened using different methods and settings, and they just don't look high quality. Larger prints that I've ordered in the past have looked great. It's just the smaller ones that are giving me fits. So I'm thinking about just printing the whole order myself.

[pippin]

don't resize them.

I never resize to certain sizes - I just crop and be done with it. Let the printer handle it.

[pippin]

Originally Posted by jeffkohn

Sorry but that's just not true. They may be able to accept files at 100ppi and make prints, but that is not the native resolution they're "running at". They're probably running at 300ppi or 320ppi depending on if it's a Fuji or Noritsu (and there may even be a few models that run even higher). When you feed these printers a 100ppi file, they interpolate it.

Jeff, I stand corrected.

[JohnT]

OK. I'm going to redo the whole order, based on what I've learned here, and resubmit it. The client has waited this long so another three or four days won't make any difference.

Thanks, everyone.

[andyz]

I've not sent a print order to a lab. But I would think they'd have a customer service rep or document that explains this, don't they?

The closest I've come is SonyImaging or something where I had some gifts made. During the upload process it would tell me if the picture was sufficient for what I wanted to do.

[barP]

smugmug (ez prints) works the same way. doesn't matter what dpi you save the file at, they ignore it. just send them all the data you can!

wp.