Love at second sight? Another look at Microsoft’s HD Photo format

Posted by Wolfgang Gruener

Chicago (IL) – About a month ago, we wrote about Microsoft’s newly proposed HD Photo image format as a replacement for the aging, but generally accepted JPEG. Our conclusion was that it is a moody format that can, but not necessarily produces smaller or higher quality files than JPEG. We talked with Microsoft about this and it turns out that, on a different angle, HD Photo in fact has advantages over the good old JPEG.

 


A closer look at Microsoft's HD Photo image format ...

 

There’s hardly any computer user out there who isn’t handling digital images on a daily basis. With a gazillion photos made with digital cameras every day digital images have transitioned from luxury to a commodity within a few years; saving and storing images has become a routine few of us are paying attention to.

This scenario alone questions the chances of success for a new image file format. Why would we transition to HD Photo, assumed that it is better than JPEG, if what we have today is good enough? Wasn’t that exactly the reason, why JPEG2000 never got a foot on the ground and doesn’t JPEG with a reasonable amount of compression enough quality for viewing your vacation pictures on the LCD or your family room TV?

The answers to those last two questions are obviously yes and Microsoft really wouldn’t disagree with that. The problem, however, is that what is good enough today may not be good enough anymore tomorrow. Why? HD Photo isn’t really just named HD Photo because “HD” is a buzz-word these days; it is in fact capable of displaying more image information than JPEG and, according to Microsoft, it can show more image information than the average LCD is able to display today.

 

The HD Photo window in Photoshop CS3 

 

So, understanding the advantage of HD Photo requires the user to look at the format from the right angle. From a consumer view, there are two main aspects.

First, handling high-quality, professional images is complicated today. Processing RAW formats isn’t what everyone wants to deal with, despite the fact that the differences between JPEG and RAW images can be stunning. Microsoft’s HD Photo tries to bridge the gap between JPEG and RAW and hands the consumer a bit more control over the image, if he chooses to fine-tune an image.

Second, HD Photo is really a format that may begin to show its potential when we all have a bit more HD everywhere. Today, the differences in image adjustments can often only be seen when an image is printed. Down the road, Microsoft hopes that better HD LCDs will bring out more image information and more vibrant colors in an HD Photo image than in an image that was saved as JPEG.
Perhaps most intriguing is the prospect of high-dynamic range (HDR) photography. What is a niche-application today (but can reveal stunning results) could move into the mainstream in the not too distant future: CCDs and CMOS sensors of digital cameras are capable of recording much more image information than is shown in a JPEG image today and, according to Microsoft, it is likely that we will be seeing cameras that directly create HDR images, without requiring the user to take a series of shots with different exposures and then merge them together into a single image. If HDR becomes a mainstream application, HP Photo’s adoption could accelerate dramatically: HD Photo supports 32-bit HDRs, JPEG does not.

File sizes and image quality revisited

As long as HD hasn’t penetrated more of our everyday lives, we will have to look at the traditional advantages of image formats: File sizes and image quality.

Over the past few days we have compared HD Photo with JPEG and TIFF file formats, with images originating in RAW format. We are limiting the illustrations in this article to just one image that provided about average results to allow a better and more obvious comparison. (Please click through our image gallery to see the images.)

 

This example uses a 5.2 megapixel image with a resolution of 2560 x 1920 pixels, which checked in at 14,429 KB in lossless TIFF format and 3025 KB in JPEG without compression.

Full JPEG compression resulted in a 185 KB image that revealed the famous JPEG artifacts immediately; however, the image was still presented in a somewhat acceptable quality. Full compression in HD Photo reduced the file size to only 45 KB, but the actual image quality was far away from what we would consider acceptable. Especially color distortions appear to be a problem for HD Photo at high compression rates. It certainly is always a matter of personal taste what is the minimum acceptable image quality, but our test image here arrived in a range what we perceived to be acceptable at a compression ratio of about 65% - and a file size of about 125 KB.

Even on a HD monitor, it was difficult to determine what exact HD Photo compression would reveal the same image quality as the 185 KB JPEG. From our subjective view, parity was reached at 61% compression and a file size of 145 KB, which would translate into a 22% file size advantage for HD Photo in this specific case.

However, this 22% advantage only applies when the image is viewed as a whole. Zoom in those details and you see that HD Photo creates substantially less artifacts than JPEG and is capable of creating smoother color transitions – at the expense of sharpness. We have seen file size advantages from only 5% to about 45% in our tests over the past few days. In that sense, we still believe that HD Photo is just as moody and unpredictable as any other current image format, such as JPEG or PNG.  

But HD Photo’s advantages aren’t really revealing themselves on the lower end of the spectrum. Move to HDR imagery and the format shows its strength. Photoshop users can save a 32-bit HDR image in six formats (Photoshop, Large Document Format, OpenEXR, Portable Bit Map, Radiance and TIFF.) In TIFF, our uncompressed 6 megapixel HDR image came in at 73,582 KB. The lossless HD Photo version, which showed no visible differences in quality, even in details and under 16x magnification, saved the image in about half the time and packed the data into only 24,487 KB.

These results clearly suggest that HD Photo’s time may not have come yet. As long as JPEG is simply good enough for the mainstream, there is little incentive to switch from JPEG to HD Photo. However, enthusiasts and professional users can already see what the future may bring and save a boatload of room by using the format. Even in times of Terabyte hard drives, image size matters, especially if we are talking about a difference between 75 MB and 25 MB.

We will be spending more time with the format and present updated test results as soon as they are available. We invite you to let us know about your findings as well: Send us an email through the contact form or simply add your comment at the bottom of this article. HD Photo is available as a free download for Adobe Photoshop CS2/CS3 from Microsoft’s website.