Resizing / Printing Images Question

TeamSpeed's example from Sam's Club is the perfect example of what happens in 99.99% of cases where you are making photo prints in a "lab" setting. You are interacting with the labs software on it's server, be that directly on the kiosk in the shop, or via the web. The system will generally ignore any value inserted in the DPI/PPI field of the Exif data, and simply look at the number of pixels provided, and the print size requested. Opening another can of worms that really should stay closed my understanding of most of these systems is that if there is no colour space specified it will assume sRGB, just as the web does. If there is a profile associated with the file then it will colour manage the image correctly.

Very occasionally you will find a lab that has an option which will require that you ensure that you correctly size the number of pixels to match the size of the print, and the PPI resolution that the printer works at. On top will be the requirement to sort out the correct colour profile to use. These labs are usually quite few and far between, and will make the requirements of this option very plain when using it. I actually use a lab that offers this service, they literally feed the file into the printer without even checking it first, but you do have to also accept that unless their is some obvious physical fault with the print, you bought it. I like this service since it is about as close as I can get to owning my own Fuji wet lab system. Oh and they say that you are very unlikely to not find a print made with sRGB instead of the actual paper profile unacceptable colour wise. Not saying that you couldn't see a difference between a pair of prints side by side though.

Alan

canongear wrote in post #18690193
Not to stir things up but, I was at the camera store this morning to pick up my pictures and had a chance to ask the person who is involved with their printing process if 72 px/in vs 300 px/in makes a difference and was told yes it does.
Pixels per inch was specified when I asked.

They said that because I was changing the file size with edits/cropping, 300 px/in should be used and not to use 72 px/in.
There might be other reasons as well but we didn't have a detailed conversation about it.

I told them that I used Lightrooom to make edits/crops to the pictures before exporting the images to the desktop and then eventually to a flash drive.

I take the flash drive to the camera store and download the images to one of the kiosk machines and then that information is sent to the in store printer.
Not sure what brand printer they currently use but at one time a few years ago I was told that it was a Epson brand and a state of the art one.

This store uses dry lab printing process.

I'm sure there will still be disagreements about this but, for myself, I'll stick with using 300px/in.
The pictures turned out nice.

Proof that the folks running the stuff do not always have any idea what they are talking about!

What makes any photo '300 dpi' is merely PixelCount / PrintInches = DPI

Provide a 2400 x 3000 pixel file, print to 8x10 and you end up with 300 pixels per inch
Provide a 2400 x 3000 pixel file, tell the printer to print to 4x6 and you end up with 600 pixels per inch
Provide a 2400 x 3000 pixel file, tell the printer to print to 16 x 24", and a lot of printing services will tell you 'You need to send me a 300 dpi file',

which really means 'You need to send me a file with 4800 x 7200 pixel file (to maintain print quality)'
and not 'a file with '300 embedded' in the EXIF (because I need that value in the EXIF)'

BigAl007 wrote in post #18690347
TeamSpeed's example from Sam's Club is the perfect example of what happens in 99.99% of cases where you are making photo prints in a "lab" setting. You are interacting with the labs software on it's server, be that directly on the kiosk in the shop, or via the web. The system will generally ignore any value inserted in the DPI/PPI field of the Exif data, and simply look at the number of pixels provided, and the print size requested. Opening another can of worms that really should stay closed my understanding of most of these systems is that if there is no colour space specified it will assume sRGB, just as the web does. If there is a profile associated with the file then it will colour manage the image correctly.

Very occasionally you will find a lab that has an option which will require that you ensure that you correctly size the number of pixels to match the size of the print, and the PPI resolution that the printer works at. On top will be the requirement to sort out the correct colour profile to use. These labs are usually quite few and far between, and will make the requirements of this option very plain when using it. I actually use a lab that offers this service, they literally feed the file into the printer without even checking it first, but you do have to also accept that unless their is some obvious physical fault with the print, you bought it. I like this service since it is about as close as I can get to owning my own Fuji wet lab system. Oh and they say that you are very unlikely to not find a print made with sRGB instead of the actual paper profile unacceptable colour wise. Not saying that you couldn't see a difference between a pair of prints side by side though.

Alan

I have never send files in. If I need something printed the I make sure PPI is at 300 (for my place as requested), export with LR and come down with the a stick. Interesting about most ignoring the PPI.

digital paradise wrote in post #18690206
Of course it does in printing. It is critical. It doesn't for images you post here, facebook, email, etc. Yes PPI is the correct term for how we print. DPI is for 4 colour offset printing.

How would you explain the fact that I have supplied a file with a predetermined number of pixels (e.g., 3888 x 2592 from a Canon 40D RAW file) processed thru LR,
with '300' embedded in the EXIF data of the JPG by LR, and then instructed Costco to print a 4x6" and a 5x7" and an 8x10" print,.. and that the three sizes resulted in different values (648, 518, 324 respectively) for Pixel per Inch -- which did NOT match the '300' within the EXIF data! -- and the conflict did not matter at all.

The issue is not that the automated service can’t print your image without the tag- the problem is their modification of your output to conform to their standard output requirements. This mostly has to do with their resizing prior to printing and the control you lose when sharpening for output.

They will print practically anything and everything with no care for PPI tags or embedded color profiles. The question is, is the result visually what you wanted? Ideally you would know their PPI requirement and resize and sharpen for output to the exact pixel dimension so that there will be no resizing done for printing to the desired print dimension. This way your output sharpening stays intact as you want it.

Kirk

Ding, ding ding.

We hav a winner!

Wilt wrote in post #18690389
How would you explain the fact that I have supplied a file with a predetermined number of pixels (e.g., 3888 x 2592 from a Canon 40D RAW file) processed thru LR,
with '300' embedded in the EXIF data of the JPG by LR, and then instructed Costco to print a 4x6" and a 5x7" and an 8x10" print,.. and that the three sizes resulted in different values (648, 518, 324 respectively) for Pixel per Inch -- which did NOT match the '300' within the EXIF data! -- and the conflict did not matter at all.

I can't because I rarely print and all I know is what I learned in classes about 8 years ago. You base your PPI on the printer that will be used.

kirkt wrote in post #18690242
Their server is calculating the implied PPI in your file and comparing it to their minimum PPI requirement. There is no need for a tag, you implied the PPI in your file when you gave them the file (in pixels on the long edge) and specified the size of the print (in inches on the long edge). Their PPI requirements are what trigger the warning you noted - you could avoid that warning by knowing their requirements (PPI) and making sure your file had the pixel count to satisfy it for the print size you were ordering.

kirk

I had hoped that was what I had stated prior to what you quoted? Sams Club minimum DPI is 175, but it isn't really advertised anywhere for the consumer, at least not easily accessible.

And this proves the point that the end consumer really doesn't need to know this setting, if the service provider is kind enough to program for that before they submit the files to the printers. Isn't technology here to make us more ignorant of details, facts, and calculations, and to keep things simple for the uneducated?

This thread could have been done about 3 - 4 replies in, with a simple "don't worry about the DPI value, just make sure your image pixel height and width satisfies the equation 'Desired Print Height x 300' x 'Desired Print Length x 300', so for a 4x6, 1200 x 1800 or better", since 300 is one of the most common DPI printing guidelines.

For the business owner that is very heavy into different print formats and quality needs and working with a quality print lab, then a more complicated answer might be warranted.

digital paradise wrote in post #18690415
I can't because I rarely print and all I know is what I learned in classes about 8 years ago. You base your PPI on the printer that will be used.

Those days have come and gone though. It was huge back in the day with inkjets really hit the market and each manufacturer was trying to one-up the other with DPI values. "Our printer is 600dpi... Well ours is 1200dpi... etc". Much like today's ISO levels on a camera, or resolution... Things have long since standardized a bit more, or the software has made life a bit easier for the consumer so they don't need to know all these terms and values.

thanks for the guideline.
hX300
wx300

TeamSpeed wrote in post #18690458
Those days have come and gone though. It was huge back in the day with inkjets really hit the market and each manufacturer was trying to one-up the other with DPI values. "Our printer is 600dpi... Well ours is 1200dpi... etc". Much like today's ISO levels on a camera, or resolution... Things have long since standardized a bit more, or the software has made life a bit easier for the consumer so they don't need to know all these terms and values.

Thanks for the info.