Downsizing hires digital photos

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drm
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Downsizing hires digital photos

Post by drm » January 28th, 2009, 10:17 am

So I've upgraded from a 3mp camera to a 10mp camera. That means that my photos are now considerably larger, and when I downsize them for websites, they need to be a much smaller percentage of the original than they used to be, like 10% instead of 30%.

The problem is that when I do that, the resultant photos show a lot more of that under-resolution problem where solid colors like the sky have lines across them where the shading changes slowly. It seems that I need to keep these new photos to 30% or original to avoid that problem, despite them being 3 times as large as the older ones were.

This doesn't make sense to me. It seems that if a 400 pixel-wide photo was good enough for the web before, it should be good enough now. Even if the the original is 3+ MB instead of 1MB.

Anybody else have this experience?

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RobFromRedland
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Re: Downsizing hires digital photos

Post by RobFromRedland » January 28th, 2009, 12:23 pm

What program are you doing to do the resizing? I've had good luck downsizing my 7MP photos for the web. I usually do 800x600 resolutions for the web or for email. I use the Irfanview program for most of my resizing
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Sore Feet
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Re: Downsizing hires digital photos

Post by Sore Feet » January 28th, 2009, 2:08 pm

drm wrote:So I've upgraded from a 3mp camera to a 10mp camera. That means that my photos are now considerably larger, and when I downsize them for websites, they need to be a much smaller percentage of the original than they used to be, like 10% instead of 30%.

The problem is that when I do that, the resultant photos show a lot more of that under-resolution problem where solid colors like the sky have lines across them where the shading changes slowly. It seems that I need to keep these new photos to 30% or original to avoid that problem, despite them being 3 times as large as the older ones were.

This doesn't make sense to me. It seems that if a 400 pixel-wide photo was good enough for the web before, it should be good enough now. Even if the the original is 3+ MB instead of 1MB.

Anybody else have this experience?
When you resize a picture to 400 pixels wide, it has to do a lot of averaging and interpolating of each pixel to achieve the final 400px image. A 3mp image would have appx 2048 pixels on the long edge of the image. Shrinking that down to 400pixels requires a reduction in size of 512%, so basically every 5.12 pixels will be averaged to a new pixel on the 400px wide version. A 10mp camera would have appx 3648 pixels on the long edge. Shrinking that down to 400px requires a reduction of 912%, so you're basically almost doubling the number of pixels that have to be averaged in order to get that single pixel in the 400px version of the image. So it has nothing to do with the width of the final image, it has to do with how much you're trying to cram into that space.

The other thing to keep in mind is resizing large images like this to sizes smaller than 640x480 will very often (almost always) result in distortion of the detail in the picture. Images 400px on the long edge really shouldn't be used for anything other than like a preview image, because you're sacrificing a huge amount of detail when you make them that small.

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sparklehorse
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Re: Downsizing hires digital photos

Post by sparklehorse » January 28th, 2009, 8:16 pm

I just rely on my image hosting site for resize purposes. With my camera (Nikon D80) I always shoot JPEG-Large-Normal, which produces 10mp images with reasonable filesizes, typically 2mb-4mb, yet excellent quality. I always just upload my full size images to my image hosting site, which happens to be Smugmug. Since the file sizes are reasonable the uploads don't take that long and since they don't limit your storage space at Smugmug I upload as many as I want. I might crop them first using Photoshop, or color correct, adjust levels, sharpen, etc, but I don't resize them before uploading. When I use the photos somewhere else on the web, such as the Ghost Ridge trip report I just did on this site, I let Smugmug do the resizing. I get a url link to the photo from it's Smugmug page and paste that url into my report text. Typically I'll just grab the "large" size link, which always ends with "-L.jpg". I don't like that size, so I replace the "-L.jpg" with "-700x469.jpg", which tells Smugmug to resize the image to my custom size of 700x469 pixels, a size I find seems to work well on most folks monitors. Smugmug's downsampling algorithm seems to work pretty well. I have no complaints about the sharpness or quality of the reduced images and haven't noticed any "banding" isssues, such as you had mentioned having trouble with in the sky area. I'm not familiar with other image hosting sites but I suspect you could likely do something similar with some of them, perhaps not the freebie ones.

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The C-Ws
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Re: Downsizing hires digital photos

Post by The C-Ws » January 30th, 2009, 4:45 pm

I have a 12MP Canon Xsi and I always use the highest resolution. I then make downsized copies for posting using a free program called Easy Thumbnails. I downsize my pics to 800px on the long dimension and that has worked fine for me so far for posting online.
Casey

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