Printing large images

[rob_garsson]

<p>I know this has been asked here before I'm just trying to wrap my head around it. I'm adjusting images shot on a canon 40d (10mp) to make 20x30 prints. Currently my images are sized at 8.64x12.96 @ 300dpi. Obviously I'm not going to get a true 300 dpi print from this. My question is when I adjust my image size in Photoshop I can leave the "resample image" box checked or unchecked - checked, it will proportionately increase my pixel size when I increase the dimensions and leave my image at 300 dpi; unchecked, it will leave the pixel size intact and when I increase the dimensions lower my DPI. Will either one of these make a difference in the quality of my print or will it be exactly the same?<br>

Also, I've heard of software that exists for this type of thing, getting files ready to be made into big prints. Any recommendations on these?<br>

Thanks.</p>

[jim_momary]

<p>That image size/dpi thing is raising its hackles again ...<br>

As a starter, bkg. info -<br>

<a href="../beginner-photography-questions-forum/00YlaA">http://www.photo.net/beginner-photography-questions-forum/00YlaA</a><br>

Best explantion I've seen in a while.<br>

Jim</p>

[Greg M]

<p>Are you doing the printing yourself, or are you having a lab do it? If you are having it done at a lab, have you asked them if their equipment re-samples files for larger prints? If you have not asked, I would as they may undo whatever it is that you do.</p>

<p>The website that hosts my images (Smugmug) does resample automatically for large prints and they suggest simply uploading the unaltered original JPEG and letting them handle it from there. They use two different professional labs that do this type stuff for a living so that's exactly what I do and I recently received a beautiful 30x40 print on metallic paper from a 12 MP camera.</p>

[ellis_vener_photography]

<p>Much depends on the printing process.<br>

 

<p>If you are working with a pro level Epson, Canon or HP inkjet printer you can make pretty good quality prints by feeding the printer a file with a <strong><em>document resolution</em></strong> as low as 180<strong>ppi</strong>. And the printer will do a good job of interpolating it up to its <strong><em>native printing resolution</em></strong> of 360<strong>dpi</strong>. A large print does not need to be at quite the same resolution as a small print because you will stand further away from it to see the whole thing. If you print the same image at the same size, one at 180 dpi and one at 360 (300 in the case of Canon) dpi - you might very well see a difference. </p>

<p>And that is before you do any interpolation (enlargement).</p>

<p>How to get there in Photoshop </p>

<ol>

<li>If you are working with Photoshop open the file at its full resolution - based on your numbers that is 2596 x 3888 pixels.</li>

<li>Starting at Image in the menu bar, go Image > Image Size and uncheck the Resample Image option. In the Document Size pane notice that you have now tied Width, Height and Resolution together but have not changed the Pixel Dimensions. </li>

<li>Type in 20 (or 30) into which ever is the long side of your image, height or width. Notice that the other two variables change. If the width is now 30 inches, height will now be 20 inches and Resolution will be 129.6 pixels/inch</li>

<li>At this point you can either click the "OK" button or turn the Resample Image option back on. If you do the latter you can now interpolate the data to the resolution you desire.</li>

</ol>

<p>Interpolation:</p>

<p>When you turn the Resample Image option back on notice that in the Document Size pane that Resolution is no longer linked to Width and Height, that the pixel dimensions are now active again and that the drop down menu for types of interpolation (Nearest Neighbor, Bilinear, Bicubic, Bicubic Smoother and Bicubic Sharper) are now available. Depending on the subject content one of the three Bicubic options will work best. Many people feel that Bicubic Sharper works best whether you are interpolating to a larger or smaller size But I really think you have to look at image content to see what works best. </p>

<p>Change Resolution to 180 pixels/inch. Now the Pixel Dimensions have changed (should now read 3600 x 5400 instead of 2596 x 3888) but that in the document pane only the resolution has changed. Now click the "OK" button.</p>

<p>To use a plug-in like Genuine Fractals or not?</p>

<p>It depends on the image and you. People I look up to for their knowledge of Photoshop, specifically Mac Holbert and John Paul Caponigro (web search them if interested) believe that Photoshop works fine until you get up to 500% of the original image size and after that it is best to use Genuine Fractals. If you think Photoshop itself isn't doing a good enough job it is worthwhile to try GF.</p>

<p>What about if you are not using an Epson, Canon or HP printer?</p>

<p>It is very likely that whichever printer your lab service or service bureau is using has its own internal interpolation scheme that will automatically do whatever math gymnastics needs to be done. All you can do in this case is send them the best quality file you are capable of making. </p>

 

</p>

<p> </p>

[rob_garsson]

<p>Thanks for the responses thus far, especially the lengthy one from Ellis, I feel I've gained some knowledge reading through here.</p>

<p>One of the reasons I have to resize my images myself is because I print at Costco, and if you don't size your image proportionately to the size you are printing they will automatically enlarge and crop it for you to fit the full image on the print.</p>

<p>Anyways I got about a dozen 20x30 prints done - from my 10MP 40d this comes to roughly 130 dpi - and I have to say I was incredibly impressed with the results, a lot better than I expected. The images printed there from my 4x5 scans came out with noticeably more detail, but I'm still quite happy with the 40d prints.</p>

<p> </p>