eBirdseed.com Wild Bird Feeding Blog

Hi all,

First things first… Don’t forget our new contest is ongoing, but it ends precisely at 11:59 PM EST, June 30th, 2007.

Back to the usual stuff...

I spent considerable time worrying over the detail of this post... Part of me wanted to just pop this one out... But it just shouldn't work that way...

If you think back to the June 5, 2007 entry (Building a Post), Gerry basically had three questions:

• "I would like to know what setting do you take the photos at?"
• "Specifically, now that Digital Cameras can record at 10 megapixels and up, it makes for better photos... but not for the web since the web has an issue with the larger file sizes that result from higher megapixel settings."
• "I read a lot about "Optimizing" photos for web use. How does that work for this blog?"

I sort of stumbled around the first two questions and left the last for this post. (There's a very good reason for this... The real explanation for "optimizing" photos is fairly technical. If you're not "into" the technical, the rest of this post will probably bore you.) With that, here's the deal with photography (especially digital) and the Web...

As I see it, there are four definitions/considerations that get all jumbled. They are:

• Pixels/Pixels Per Inch (PPI): The word "pixels" stands for the phrase "picture elements". In fact, a pixel is more than just a finite element - it's more an equation than a fixed quantity. Probably the best way to look at pixels is to look at their source - typically a digital camera or a scanner. (For the sake of this post, I'll "focus" on cameras, and particularly the NovaBird.) When you take a picture with a camera, the analog image passes through the lens, through the image sensor, then is exposed to a CCD or CMOS matrix, which completes its journey from the real world of analog to the digital world of pixels. The size of the matrix determines the size of the shot in pixels. Depending on the number of bits used to describe the pixel further controls the size of the final image in the camera. In the case of the NovaBird, the raw image is 2,048 x 1,536 = apx. 3 million pixels (a.k.a. 3 megapixels).
  
  And if only the discussion were to end there, this issue just might appeal to common sense. But it doesn't end there. In fact, the confusion is just beginning.
  
  The number of computer bits (8 bits make up one byte) used to describe a pixel varies, but I'll use the 24 bit standard... That means that each pixel is described by 3 bytes, and that a 3 megapixel photo is in fact around 10 megabytes (MB) in size. (Ever wonder why bmp files are so big?) Unfortunately, 10 megabytes is big... Real big. (To put that in perspective, we use a 256 MB SD RAM card in the Nova', and if we tried to store 10 MB files, the camera would only hold about 25 pics.) Uh oh... So here's the deal... The camera automatically compresses the raw image into an efficient format (*.jpg) that will occupy only 0.5 MB - that way the SD card can hold around 500 images. (If you want to know more about data compression, just use the "comment" button below.) Can you see the water starting to muddy?
  
  Now we have a 0.5MB jpg file which holds 10MB of image information which is 2,048 pixels wide, and we want to cast it upon a monitor/video card/video driver that supports a max of 1,600 pixels side to side (PPI). Oh goody. Needless to say that programs like Microsoft Office Picture Manager play some cute mathematical games when it comes to making a single image "fit" the screens of a Mac, a PC, a laptop, all at the same time...
  
  Yes, the water gets muddier still. Onward.
  
  
• Human eye: So what is acceptable for decent graphic presentation on a computer (let alone Web optimization, as Gerry asked)? Well the average human eye can discern the slightest color change in roughly 300 PPI (or 1" of display showing a gradient of 300 slightly different pixels).
• Computer Monitor: This is where the fun goes goofy. For computer screens, the typical pixel sizes are apx. 0.4mm (0.016") square... The really bad news is that computer screens usually have a max resolution of 90 PPI. (Classically, Macs are 72, and PCs are 96 PPI). Doubt it? Check out the duplicate picture(s) below.
  
  The photo on the left was saved at a resolution of 72 "DPI" vs. the picture on the right that was saved at 250 "DPI". (See the next item for a rant on "DPI".) See any difference? Nope. They're pretty much identical. That's because today's PC monitors adjust everything to ~ 96 PPI.
• Printers (DPI): As if all this wasn't confusing enough, the measure of "Dots Per Inch" (DPI) gets thrown into the mix, and is confused with PPI. Let's get this clear... PPI is the land of cameras, scanners, and monitors. DPI resides in "Printer World". Contrary to what the kid down at the Big Box Appliance and Computer store tells you, PPI does not equal DPI. DPI is a measure of the number of dots of ink a printer can lay down to create a certain image resolution. And the higher the original PPI, the more the picture can be expanded and printed on a printer with a fixed DPI. (Ever wonder why some pictures can be blown up and printed while others just look like crud? Now you know.)

So Gerry (if you're still awake), the way that pictures are "optimized" for the Web is a process of taking the picture at a reasonable resolution (PPI), sizing and "enhancing" it to adjust the brightness, colors, sharpness, etc., to match the original subject, and then saving it at a resolution matching that of the destination monitor. Typically that would be 96 PPI.

Do I do that? Naw! I try to work at 250 PPI. Why? Because the image sizes that we work with are 300 - 400 pixels max on a side. The eBirdseed server can handle the load. True, they're higher resolution, and that won't be at all different on your screen right now... But just wait... HD monitors are coming, and when they arrive, this blog will be waiting with open arms. Also every picture in the New England Bird Picture Library is roughly 250 PPI, which means that folks can download those pictures (for free), and use them without fear of early "pixelization". How's that for a value-added blog?

I'll be leaning on the tripod over by the feeders,

CapeCodAlan

P.S. And just how good are pictures saved at such high resolutions? Take a look, but be patient.