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Resampling to make your images bigger
Some thoughts on when and how to resize images
Never be afraid to go back and re-evaluate your workflow.
There is nothing wrong with changing a technique you have done for a while when something better comes along.
Keith looks at how changes in software can alter the way you work.
When to resample/resize
Just after first I wrote this article, Photoshop CS2 was formally announced, with new versions of Adobe Camera Raw and a much improved file browser.
When I wrote the article 'Why use RAW camera files', the upsizing option in Adobe Camera Raw (ACR) was an excellent place to increase the size (number of pixels) in the file you created.
That was before the advent of the two new methods of resampling images that appeared in Photoshop CS.
Actually ACR still is excellent for this, but it depends on what you are going to do with the images produced...
The two new methods Bicubic Smoother and Bicubic Sharper are designed to minimise the amounts of sharpening artefacts (smoother) or loss of detail (sharper). You use Smoother when upsampling (bigger images) and Sharper for downsampling (smaller images). Remember that this applies where you are changing the actual number of pixels in the image (resampling). If you just change the resolution (say from 360 dpi to 240 dpi) you will get a different size print, but no change in the actual image data. One of the nice things is that once you get to a certain image quality, you can print large prints at a lower resolution anyway, since big prints tend to be viewed from a greater distance.
I always use Bicubic Sharper when creating web images, and often apply some extra Unsharp Masking (USM), particularly for thumbnails (see the photos for the web article for more info). Note that you may want to use one of the other methods (such as nearest neighbor) for graphical images where you want to retain sharp edge transitions.
The upsampling in ACR can produce more artefacts when used, as opposed to Bicubic Smoother. The example below is from a Canon 1Ds raw file.
The Black Canyon of the Gunnison in Colorado.
This is the original image that I used for a black and white print
Resampled to 4088x6144 in Adobe Camera Raw
Viewed at 300% magnification
Resampled to 4088x6144 in Photoshop CS using Bicubic Smoother
Viewed at 300% magnification
Ok, that looks pretty clear, don't use ACR for resampling. But, hold on a minute, what about in the real world where people do not look at prints with pixels the size of match heads?
Before I would print any picture I would sharpen it anyway (I prefer to do this last since the amount of sharpening varies with print size) so any small amount of artefacts may well be lost in the printing process. What might look clear cut from the examples above is not necessarily the way to go.
At the moment (early 2005)...
If I'm supplying 300dpi TIFFs for a client from a shoot and they want pics at one of the sizes below, then I'll use ACR (I have several automated workflows that work very well)
If I'm going to be producing prints at a variety of sizes for sale and exhibition, I'll use Bicubic Smoother to get a bigger file size.
I'll also do this if I've used DxO for my raw conversion. I'll also put a lot more work into the images getting them just right for what I want.
The tricky one comes when I need to produce a very large print from an image I originally upsampled with ACR -- depending on the amount of work involved I may go back to the original raw file and re-convert it. Now -that- is one of the real advantages of shooting in raw format.
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As I write this, Photoshop CS2 is about to come out -- maybe there will be improved functionality in ACR, I don't know. But it never pays to become too attached to one element of your workflow :-)
Oct 2005 - I've written an article about the technical image processing and resizing issues that I came across when producing 29 prints (up to 78"x43") for a large exhibition of my work. One more reason I'm glad I have the original RAW files to go back to if need be.
2009 Improved RAW converters have improved the quality of my images, but I still use combinations of ACR, DxO 5 and Nik Sharpener 3 for a lot of work, although I prefer to do the resampling after RAW conversion.
The views in this article represent those of Keith Cooper.
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