Monday, February 18, 2008

So How Many Pixels Does It Take To Make A Face?

Maybe more, maybe less than you think - it all depends on the size of the face in the image. In my early digital days (like 6 years ago) of digital photography, I was shooting with a Fuji S-1. It was the hot camera on the market roaring on the the new digital scene with 3000 pixels! It was hyped as a 6 meg camera, but opening the file in Photoshop yielded a 2040px x 1353px image dimension. Nevertheless, DPreview said, "Look out boys, Fuji Film are in town and they mean business." You can read the August 2000 review right here.

I remember shooting my first wedding with it in December 2000 - I was scared to death - ahh, where's my film, but all went really well and I was a digital convert. I imerged myself into learning the ins-and-outs of the camera , did some "portfolio" shooting with it and carried an album with me to the 2001 Photo-East show. A friend of mine was a upper level manager at Fuji and heard I had a wedding album of all Fuji digital images with me. He had - get this - the president of Fuji USA come by (I was working another both at the show) to take a peek at the album. I was floored by his remark. He said quietly to our small group, "Wow! These images look better than our film images." Heck, I thought so to. I was a nice compliment and I was on "Cloud 9."

Fast forward a few more months - I was a really happy camper with my new camera and was loving the digital experience. I wanted to get some more samples made up for the studio and since I was beta testing the now defunct ProShots software at the time. This allowed me to work with a lot of labs across the country and have access to their backroom digital gurus. I remember sending some images in for printing, some of which were large wedding party groups where the actual individual subject's head size was quite small. I get a call from the lab and the technician saying he might have some trouble printing the group photos. I was shocked - what do you mean trouble printing the group images. His words still ring in my mind. He said, "yea, trouble - you only have 20 pixels from "ear to ear" on each individual. Now it made sense - it wasn't like film made up of a lot of tiny silver halide specs - it was the fixed amount of "photo receptors" from left to right on that chip that defined the resolution of the image. The reality was - big heads, no problem, small heads, big problem.

If you have a photograph of a large wedding party, say made at a park, the head sizes of the wedding party members can be quite small. But how small is too small in our current digital age? I always thought it was such a "hoot" in the early days, because every time I visited the trade show booths of the digital camera manufacturers, they only showed large head sized images of their "people" pictures - NEVER anything like a wedding party image. Well, when you drag all those pixels across one large face - no problem. It's the 20+ members of a wedding party standing shoulder to shoulder across the frame that really reduces the number of pixels available per head, and that's where the camera's resolution is an issue and needs to be considered when selecting a camera for wedding photography.

So how many pixels does it take to make a face? I'm going to let you decide. Take a look at a recent wedding party group shot I made last year. I was shooting with a Canon 5D - 12.7 mega-pixels with the image size measuring 4368px x 2912px. Pretty darn good - a far cry from the old days (isn't kind of funny that the old days weren't all that long ago.) I know what you are thinking - man, Ziser, you don't even have them "shoulder to shoulder." Well, I did have 12.7 mega-pixels to play with though. Anyway, here is the deal - how many pixels at full res are defining the head of the fourth groomsman on the right? How about 77px from ear to ear - not many - but still enough for the image to look just fine. Now let's rewind back to 2001 when I was shooting wedding with the Fuji S-1 - 2000 pixels total in the horizontal direction. It's no wonder the lab tech was so concerned - 20 pixels was not enough to define the face clearly. So let's take a look at how many pixels it takes to define a face and you be the judge.

Look at the first image below. I took the wedding party photo, reduced the resolution in 1000 pixel increments, did a screen capture to preserve the pixel structure of the image so you could really see the difference. As I changed the resolution from 4368px -> 3000px -> 2000px -> 1000px, look how the pixel count changes on the groomsman. Total pixels describing his face range from 77px -> 53px -> 35px -> 17px.
Next, I took the images into Photoshop to smooth up so can get a true idea of just how they would print. I know the heads with the resolution from 3000 -> 2000 -> 1000 all look soft, but remember, I have the head size enlarged substantially. The groom's head would be substantially smaller in an 8x10 print. So that said, when would the image effectively start falling apart? Well, I printed a copy of the wedding photo shown at the 4 different resolutions from 4368px down to 1000px across and assessed the final printed image. Somewhat to my surprise, the images down to 2000px across looked fine - even under close inspection. Even the 1000px image looked OK at the normal viewing distance of 12 - 20 inches. Closer inspection showed it was quite blurry though. That explains the comments from the lab tech 6 years ago - I had quite small head sizes in the image in question. I learned from that experience to pose my groups a bit tighter - so I could get closer and get bigger heads in the image and to alleviate the "low pixel count" head problem.

As cameras continue to improve their resolution, the problem starts to go away. My gosh, some of the high end backs for the Hasselblad come in at 39 Mega-pixels, with 7300 pixels making up the horizontal dimension - that's means that the head of my groom taken on the Hasselblad H3D back would measure about 128 pixels from "ear to ear". But do I want to spend $25,000 for the camera - ah, no! How about the new Canon 1Ds Mark III at 22 mega-pixels and $8000. Pixel count for my groom's head would measure about 99 pixels from ear to ear. Now is that worth the added $4500 over the Canon 5D - a solid maybe.

Folks, the point of the matter is that we need the right equipment for the job. And, if the job requires us photographing lots of people in a group where the head sizes are going to be quite small, we need the mega-pixels to pull if off. For weddings, based on my subjective experience, I think 8 - 10 mega-pixel camera is about the sweet spot for the wedding shooter - the price vs. pixel count is just about right. As long as we can define a person's face with a minimum of 50 pixels across, an 8x10 image will look just fine in the album. Of course, the more pixels , the better. Try to enlarge that images to a wall portrait and things start "going south" again. In my practical studio experience, I have found that I can enlarge my wedding party groups up to about 20 inches for inclusion into the album as a two page panorama image when shot on the Canon 5D.

I was closely inspecting an 24x30 inch portrait image right now in my studio shot with the Nikon D1x - a slightly more than 5 mega-pixel camera. The head size is quite a bit larger than the wedding party images so I got away with a larger size print, but I have to say, that this was the upper limit with the Nikon D1x. My early Fuji S-1 was good to barely 24x20 inch size, depending on the head size once again. I've made 40 inch family portrait (larger head size) prints with my Canon 5D that look fantastic. My current Canon 40D's do a great job on most subject matter up to 36 inches.

So there you have it - an objective discussion on resolution and head size and what to expect subjectively. Hope it was helpful.


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  3. Brilliant. Im a CCTV installer and I have become fastinated with resolution and pixel count. I was trying to find some comparrison for pixels that make up a face and found yours. great to read your article too, VERY interesting and I like how time you've put into testing it all our for yourself. top marks. regards. Daniel