Which is sharper, theoretically - small image at 100% or large image re-sized in Photoshop?

Question

I take macro shots of watches and post them on the web (not intended for printing), typically 640x480px. I've been composing those shots in the 1504x1000px frame so that it shows the required size on-screen after cropping, i.e. it is not re-sized during processing. Although we know shooting at 3008x2000px gives greater resolution, the image has to be re-sized, for my purposes, during processing. So, while realizing that sharpness is subjective, which method should give better apparent sharpness?

Nikon D50 (APS-C, 7.8 um pixel pitch), Nikkor 60mm macro D model (usually set f/8), shooting between M = 1:1 and about 1:5.

Answer 1

Most cameras have an anti-aliasing filter that can both reduce observed detail and moire patterns, especially when the image is viewed at 100%.

The practice I follow is to do all my toning and cropping at the image's original size and then size the image down to the size I need it to be and then apply a sharpening tool to the image, like Photoshop's "Unsharp Mask" or "Smart Sharpen". This to me gives the best sharpness. When working in RAW I tend to re-size in 16-bit and sharpen in 8-bit.

Here are some pages on AA filters and using smaller images at 100% versus sizing down, with image examples:

http://www.maxmax.com/nikon_d200hr.htm

http://www.ophrysphotography.co.uk/pages/tutorialmegapixelsharpness.htm

Answer 2

I'm going to give you one more thing to think about if ultimate apparent sharpness is your goal: how well the actual details fit the pixel matrix you are using to represent them.

When you shoot at the finished size, you are stuck with the pixels the capture device gives you at that resolution. You can run sharpening and deconvolution algorithms on that data until the cows come home, but you can't change the starting data.

If you shoot at double the final resolution and do an overall sharpening first, you can change the crop before resizing. A one-pixel horizontal or vertical change in the position of the crop doesn't sound like much, but it can have a huge impact on how well the most important details (say, the maker's name or the numbers on the watch face) align with the final-sized image's pixels.

You can automate the process (crop then resize) in most image editors, giving you a one-click action to create four reduced-sized images that you can select from to create the final web image. It should be apparent that one of the images in the 4-image set is the best starting point for final output sharpening, depending on the specific detail you want to concentrate on most. It wouldn't make nearly as much of a difference with organic shapes, but it can have an enormous impact when you're dealing with fine, high-contrast artificial detail.

Answer 3

If you want the best results, you should simply shoot at full resolution in raw. Manipulate them until you're happy with the output, export to a certain size and have some sharpening applied after the resize. That's essentially how Lightroom works and I get very sharp results.

Not to mention that if you ever did want to print them out, you have nothing to print out with besides a low resolution image sharpened for the web. Unless you have deadlines or need to shoot out JPEGs quickly for use, you should pretty much always shoot at the maximum quality and resolution your camera can provide. Get the 'digital negatives' and you can do anything with them.