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DPChallenge Forums >> Photography Discussion >> Help - setting 300 dpi to print
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 03/03/2012 02:50:28 PM · #1
First off, I am not new to setting the dpi size to get the best resolution. So this experience has me just about ready to pull my hair out from frustration.

Here is the scoop

WHCC printers are requesting that I send test files for 8x10 set at 300 dpi.

The first time I sent the file size at 2400 x 3000 pixels per square inch - that will give a 8x10 printed at 300 dpi.

Customer Service Rep came back that "These files received were around 118 for resolution."

Looking at image detail information it was 2400 x 3000 set at 72 dpi .

The Steps (I have Paintshop Pro X4 now)

I begin by opening a new file setting height at 3000, width at 2400 and resolution at 300 ppi

I Copy and paste my 3000 x 2400 picture into this file

Next Save As ---Jpg - under save options I select standard encoding, save EXIF data, compression 4, and embed ICC color profile.

File saved - no problem right?
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.
.
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Well I open the saved file again and look at Image Information Window:

under image information tab:
Dimensions 3000 x 2400 pixels
41.667 x 33.333 inches
pixels per square inch 72
Pixel depth 8 bits per channel

under the next tab EXIF info tab:
x resolution: 300 dpi
y resolution: 300 dpi
resolution unit : Inches


Question 1
If it is set up at 2400 x 3000 and the preferences are locked at 300 dpi, why is it showing conflicting info that it is at 72 dpi in the Image Information Window when the x & y resolution reads 300 in the EXIF tab?

Question 2
Why is WHCC telling me that the resolution is not 300 dpi and they are showing 118?
 03/03/2012 03:08:26 PM · #2
I'm not familiar with your software -- at this point I'd suggest just using something else to change the resolution ... IrfanView is free and will do the job. As long as the number of pixels remains the same, you should be OK -- the resolution just tells the printer how large and area (physically) those pixels should be spread out over.

I agree, what you describe sounds rather bizarre ...

Hmm... if you save the EXIF data the resolution will be set to whatever the camera uses -- 118 is (for some unknown reason) one used by some models.

Go to "Image Size" and change the resolution without resampling and you should be OK.

Message edited by author 2012-03-03 15:10:50.
 03/03/2012 06:33:07 PM · #3
What Paul said. I think the person receiving your images has a common misconception. Regardless of what DPI is embedded in the file, DPI is nothing more than an abstraction until a piece of paper comes along. Then the DPI is whatever you print it at, NOT what is listed in the file info.As you thought, what matters is what it is ultimately printed at.

However, changing the listed DPI and resaving the file that way should satisfy them.

Here's an explantion I gave to Roz a couple of years back if you can use further examples:

Originally posted by Yo_Spiff:

A subject I have become familiar with, both on and off the job! I spent 6 back and forth e-mails on this subject with a coworker the other day. It's still tough to explain, however. One day I will hit on the explanation that works first time for everyone. That means you are my latest guinea pig!

DPI is a measurement of the pixel (or dot) density of a printed page (or how finely it is being scanned). The actual size of an image is measured in pixels and for a given image, that pixel count remains the same regardless of the assumed page size and DPI setting.

DPI is only an abstraction and makes no difference until a piece of paper comes into the scene. (whther you are printing it or scanning it) Some software will make a default assumption of the DPI setting, and perhaps embed that assumed setting into the file, but it does not change the actual image, it only changes the default physical size at which it will print.

Here are a couple of identical images I have done. The ONLY difference is the DPI encoded in the file, otherwise they are the identical image

600 DPI:

184 DPI:

If you printed these at the DPI encoded in the files, the 184 DPI version would print physically larger, but with the pixels spread out over a wider area. The 600 DPI version would be physically smaller, but would still be composed of the same number of pixels, just packed tighter.

The printed document size is a function of both the size in pixels and the DPI it is being printed at. For example, lets use a 720 pixel challenge entry:

At 300 DPI it prints at 2.4 inches 720 pixels(dots) divided by 300dpi =2.3 inches

At 72 DPI it prints at 10 inches 720 pixels (dots) divided by 72dpi = 10 inches

Here is an article on the subject that I found a while back Maybe this can help clarify (or confuse) it some more.

As far as your workflow, PSD is better for files in work, because it preserves your layers and other Photoshop specific information about the image. TIFF is a more standardized format however, and is preferable as a format to save the final results. In 50 years someone may not be able to open a proprietary PSD file, but the more standardized TIFF will likely be readable. TIFF is usually the format recommended for digitally saving images for genealogy work. Both TIFF and PSD are formats that do NOT use lossy compression like JPEG, so you so not lose any image quality when saving. Any compression they may use is lossless.

 03/03/2012 09:08:01 PM · #4
The only thing I can think of is that the copy and paste action into your document is transferring over something that is confusing Paintshop Pro or possibly WHCC. My RAW files say they are shot at 300DPI even though I haven't specified that anywhere. It leads me to believe this setting may be nonsense until another program actually puts some meaning into it.

Does PSP have a crop feature that lets you crop at a certain dimension and DPI? Photoshop CS5 will change the print dimensions and set DPI while you crop. Either that or open the file directly into PSP and edit the image size there. Again, unchecking "resample" will only change the directions the file is sending to the printer (i.e. DPI).

On a side note, is PSP different in regards to compression? 4 seems pretty low for prints unless the numbers are different in PSP. Just curious.
 03/04/2012 09:21:50 PM · #5
Thank you Paul, Steve, and Aaron for your replies, helpful advice, and insights.

The solution ultimately came with a service update pack to fix bugs and such. My husband checked it yesterday afternoon but there was not one in the docket. He checked late morning today and downloaded it. I just had time this evening to test it out. It reads 300 dpi in BOTH tabs of the image info data.Yea, it works now!

So it was a bug in the software:-) Test prints sent.
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