Alley in Pisa, Italy

by Lars Kotthoff

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I am working with a product photographer who is having issues understanding dpi and resolution.

She is shooting products to go onto a website using a Canon 5D and an ortery box.

I have asked her to provide three images for inclusion on the site; one at 720 pixels wide, one at 360 wide and a thumbnail at 60x60.

The issue is that Lightroom, which she is using for post processing, is forcing her to choose a width and reducing the quality of the image too far.

We need to balance quality with image size. For the 720s, an image around 500k is fine and should have enough resolution to allow users to zoom in to see some detail.

What’s the best way for her to convert the jpegs to 720 wide and maintain enough resolution for zooming?

Here's the original image 3.5mb

Here's the result after exporting from Lightroom 71k

Here's the image used on the actual website It's the last of the thumbnails. Be sure to mouse over the image to see the magnifier.

The goal is for users to be able to read small numbers on the products while maintaining a reasonable file size (500k?).

enter image description here

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This question makes no sense to me. It sounds like you want the 720 pixel image to be larger than 720 pixels, which is by definition impossible. Or do you just mean that you would like less JPEG compression applied to the smaller image? –  mattdm Feb 4 '13 at 19:45
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Honestly, it sounds to me like you actually want an image that's significantly larger than 720px that's downloadable on demand (perhaps tiled) or downloaded by a bottom-of-the-page script (so it doesn't interfere with page rendering) for the zoom function. The other alternative is to use, say, a 1440px image and let the browser scale it down to 720px for display, but that will significantly affect download-and-render times for mobile users and anyone without "real" broadband (cable or DSL "lite" subscribers as well as anyone left on dialup). –  user2719 Feb 4 '13 at 20:29
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The title contradicts itself. If you scale down you will lose quality. That is what scale down means! –  dpollitt Feb 4 '13 at 20:34
    
I changed the title to better reflect the question, to provide the files and a link to the website with the images in use. –  rboarman Feb 4 '13 at 20:45
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@rboarman "without losing quality" and "while maintaining quality" mean the same thing -- your edit doesn't address dpollit's point at all. When you "scale down" an image, you necessarily reduce the number of pixels, and by definition a lower resolution image results. –  Caleb Feb 4 '13 at 21:04
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2 Answers 2

The web site appears to be the problem here. As far as I can tell, the web site, when you mouse over the "larger" (non-thumbnail) version of the image, it shows a pannable full-size image. The problem is that the full size image is NOT full size, it is the same "larger" version upscaled in the browser (or maybe via some processing at the server). It looks as though the larger version was nearest-neighbor upscaled by 4x, thus resulting in blocky pixellation.

That would not be Lightroom's problem, that is a problem with the web site. If you choose to export an image at 720px, Lightroom will export it at 720px. The PPI (pixels per inch) setting has no effect on an image displayed on a screen. It only has an impact if the image is printed. That said, I do not believe 720px is large enough. I believe the full size image is actually a full 4x larger than the "large" version. That would mean you need an image 1440 pixel wide, not 720 pixels wide.

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1  
It's using the 720px image resource, actually, but it's not displaying it at 720px. (The actual size is buried in pages of JS and CSS, and I'm not going spelunking for it, but it's closer to 1440 and may not even be an integral multiple. It also appears that something is deliberately overriding bicubic, since the -ms-interpolation bicubic value is invalidated in the CSS.) –  user2719 Feb 5 '13 at 9:37
    
Yeah, there is definitely something wrong with whatever styles are configuring the full-size popup version, and the image is definitely larger than 720px. –  jrista Feb 5 '13 at 21:27
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The export dialog is very powerful and she can enter your request exactly as stated.

You can specify a width and height or just one of the two and Lightroom will do the right thing. For a landscape orientation image, you can simply set the Long Edge to 720 pixels and export. As shown here:

enter image description here

Either make her repeat for 360 and 60 pixels are you scale the 720 one down for her. On several websites, I code the upload form to do the downscaling automatically, so only the highest resolution image needs to be provided.

As you also see in the screenshot, you can enforce more constraints such as JPEG quality and file-size if you like. Remember that scaling down is a loss of image quality. The actual DPI setting is immaterial for your use, she should simply ignore it.

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When she export at 720 wide, as above, the resulting jpeg is way too small and way too fuzzy. –  rboarman Feb 4 '13 at 19:47
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The only reason it would be too small is if she did not have 720 pixels to start with! Otherwise, they will be exactly 720 pixels wide. With a JPEG quality of 90, degradation is very low. Usually, 85 is good enough for me but some most websites use even lower quality. –  Itai Feb 4 '13 at 19:53
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I'll upload the two files so you can see. –  rboarman Feb 4 '13 at 20:24
    
I edited the question and provided before and after images. I also included a link to the website so you can see the image and the zoom functionality. –  rboarman Feb 4 '13 at 20:48
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@rboarman It looks like an issue with your zooming software since the image in the zoom-window is much more fuzzy than the scaled one. It may even be upscaled.... in which case things will always be fuzzy and you need a larger image than 720 pixels. –  Itai Feb 4 '13 at 20:55
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