Printing preparation in photoshop question? Profile assignments, CMYK, dpi .. what?!

[superasian]

Not sure if this is the right forum for this question, but as the title states, I need some help with prepping for printing!

I was editing a dozen or so photos to put up on the web, and after editing in Lightroom I imported to Photoshop to finish editing. However, I saved them all as .png.. my mistake. Now I want to prep those same photos for printing but I just want to make sure that any changes that I've made won't adversely affect the photo in print (i.e noise, color loss, what have you). In other words, I wanted to know if editing the .png file would give me the same results if I were editing a .psd file. I have all the Lightroom edits still I think if worse comes to worse.

Things that I've changed:
- RGB to CMYK
- ~240 dpi to 300 dpi
- profile REassignment/REconversion* from sRGB to Adobe RGB

*they were all originally Adobe RGB but I converted to sRGB to 'web enhance' them, hence the 're' ; also, regarding the 'assign profile vs. convert to profile' topic, i keep finding different advice online .. what do you guys advise?

If it matters where I'm getting my photos printed, I don't have a photo printer of my own so I'll probably be using Wallgreens' .. unless you guys have better suggestions?

Thanks a bunch!!

 

[Garbz]

- Unless you're prepping an image for a commercial printing press you have no reason to use CMYK. Quite the opposite most places will actually specify that they need a file in a RGB colour space.
- The ppi (PIXELS per inch) has no bearing when sending prints to many companies since they will ask you to specify the print size and resize the image accordingly. At some high end places they may ask you to preset your image so you know how big you want it so when their printing software opens it the image dimensions are already correct.
- Most places like Wallgreens won't accept AdobeRGB. But even if they did at this point you're not gaining anything. Moving from a large colour space to a small one eliminate the original data. You have nothing to gain in converting to AdobeRGB at this point, only something to lose as 8bits are usually not enough to store the entire AdobeRGB gamut without banding. Fortunately you likely lost nothing. You have very little to gain with large colour spaces in normal images anyway. Sunsets and artificial light sources perform better but the large majority of images will remain completely unaffected.

As for saving in PNG, you haven't lost anything as long as it was a 24bit PNG. The file format is lossless. It would have flattered your layers but you won't have any image quality issues as a result of this. PNG uses lossless compression.

 

[KmH]

You might find some of the info in this small group of tutorials helpful - Tutorials on Color Management & Printing

Yes, it matters where you get your photos printed. Walgreens is ok if you don't have high expectations for print quality. 8x10 and smaller prints can be made at your local Walgreens. Prints bigger than 8x10 get made at a central Walgreens printing facility. Walgreens uses the cheapest materials and shipping methods available.

Some better online consumer print labs are Mpix.com, WHCC.com. BayPhoto.com, NationsPhotoLab.com.