A question about DPI and printing.

[MightyLeeMoon]

Okay, let's say I take a picture with great exposure and pull it into Photoshop and do a little bit of editing. After a few minutes I feel this thing is ready for print.

The current size straight from the D50 is 3008x2000 pixels. Or 10.027 x 6.667 inches with a dpi of 300.

When it comes to resizing or adjusting for clear printing on an 8x10 glossy, what needs to be taken into consideration?

What about 23x35?

Are there dpi recommendations for this? I'm doing a bit of Googling on the topic and am doing some experimentation, but am looking to the experienced folks on this board to help me with some direction and the results you have found from your own hands on know-how.

 

[Digital Matt]

Most digital printing today will be at 300 dpi. Ask the intended printer to be sure, but probably 300 dpi. For an 8x10, you'll have to crop. If you use photoshop, use the crop too, and set the dimensions to 8x10 @ 300 dpi and crop away. Same for 23x35.

 

[fotogenik]

here is the problem I have been running into. And I have yet to figure out hte solution.

I take my full rez image 3008x2000 pixels at 300dpi and crop them to 8x10 at 300dpi. I do the editing I want to do such as levels, saturation and other things, and save the tif file. then I go in to save for the web to a lower resolution (typically 72dpi). When I adjust the dpi the pixels change, so I go back up to change the pixels to where I want them and lose the print size I want.

What am I doing wrong?

Cheers,

 

[markc]

Do a search here for "the myth of DPI". Dots per inch and pixels per inch are completely different things. When all you want to do is change the dimensions of the image, make sure you aren't resampling. When it comes to the web, ignore DPI. It has no meaning. Just pick some good dimensions that you think will work, like 900x600 pixels.

And yeah, when you size for the web, you lose pixels. You can't get them back for printing later. You need to go back to a larger one you saved earlier.

 

[markc]

Setting the DPI on the crop tool can be dangerous, because it will do a resample. If you have a larger image, you will lose data. For most people you will sample up, but that often just increases file size. Basic interpolation doesn't give you any extra data.

 

[ksmattfish]

What am I doing wrong?

Set your resolution, then click off the "resample image" box, and change the dpi to what you want. Of course, once you have the resolution set it really doesn't matter what dpi you choose for the web. My web friendly size is 500 pixels across, but this forum and others doesn't care if that's set to 72 dpi or 300 dpi, it still just displays it at 500 pixels by whatever.

 

[markc]

Personally, I wouldn't mess with the DPI setting. You can't set all three options at the same time: dimensions in pixels, dimensions in inches, and dpi. You change one, and at least one of the others has to change. If you size for the web, both dpi and inches doesn't matter, only pixels. That's how it's shown. Just choose your pixel x pixel size and ignore the rest. If you are printing, leave the pixel size alone and change the inches dimensions. The DPI will then also change. If you set it to 8x10 or whatever and see that you have 158dpi, then you know that you probably won't get the greatest print from it. Extrapolating extra pixels to get 300dpi won't be helping much. If you see you have 287dpi, then you've probably got a decent print. Those numbers are just examples. I'd say anything less than 150 dpi isn't worth the bother, 150-225 might work for some people or some images, 225-300 dpi will probably work for most people, and 300+dpi is great and what you want to shoot for. It all depends on the image and how it's displayed, and for who. Print a few at various sizes and note the dpi. This will tell you what you can get away with for your own work.

 

[Digital Matt]

Setting the DPI on the crop tool can be dangerous, because it will do a resample. If you have a larger image, you will lose data. For most people you will sample up, but that often just increases file size. Basic interpolation doesn't give you any extra data.

If you want an 8x10" print, you need 2400x3000 pixels at 300 DPI, whether you resize the image to 2400 x 3600, and then use the marquee tool and "crop" it, or you use the crop tool from the get go. They both do the same thing, and there's no way around it. You have to resample the image to get the required dimensions to print.

 

[markc]

I guess my point was that 300 dpi is a suggestion, not that you should resize your image to match 300 dpi. From what I've seen, there's nothing magical about the number. If your source image is lower than that, you might have some issues with quality. Resizing the image isn't going to add that quality. If you have a 1200x1500 image and then size it to 2400x3000, it's still going to look like a 1200x1500 image, but take up more room. Sure, stepped interpolation can help, but it's still interpolation, not real data.

Basically, leave pixles and dpi alone. Resize with inches and resample off. If the dpi shows less than 300 dpi, decide if you can live with reduced quality or pick a smaller size.

 

[Digital Matt]

I've never been to a printer that let me print at any DPI I choose. Most commercial digital photo printers print at 300 DPI, and will print your file at 300 DPI, regardless of what your file say, so you should have it setup to print the size you want at 300.

 

[markc]

I haven't used any commercial printers myself, but that just seems odd to me. I know most of them recommend 300 dpi, but looking at the Mpix site, they have a lot of size options; I don't see anywhere that says you have to size it with 300 dpi. If you let them scan it, it states that the image will be 1228 x 1818. If they force 300dpi, then you could only print 4x6 from their scans, but they say you can print up to 8x10.

This is from the EZPrint FAQ:

"We should also mention that a 600 x 400 image has just enough resolution to print a 4" x 6" photo. You will notice that the ez prints application will warn you if you try to send an image that does not have enough resolution, still you will be able to bypass the warning and upload such an image, but the result will be a poor quality print in most of the cases."

So they are recommending at least 100dpi(!) and will let you do less.

From Photoworks:

"To help prevent quality problems, we display a "Print Quality" indication next to the print size of each of the print sizes that are available when you place your order. Each print size will have either "Good" or "Poor" listed next to it, which is determined by the resolution of your digital image. If you see "Poor" listed next to the print size you want to order, you might want to consider ordering a smaller print size that says "Good" next to it. However, if the resolution of your image is very low, you may see "Poor" listed next to all of the available print sizes."

I understand where the idea came from. A lot of local labs tell people that the images have to be at 300dpi, but I think it's to prevent people from being disapointed and wanting a redo or money back. They didn't consider that people would just resize and still get a lousy print.