Tuesday, November 1, 2005

Depth of color and his and her photo albums


By David Gewirtz

Connected Photographer regularly gets a ton of reader questions. We try to answer them, but with thousands of messages a day coming in, I'm sure we miss a bunch. I've had a long list of backlogged Letters to the Editor, so I decided I'd knock out two of them today. They may answer your questions as well.

His and her photo albums

Our first question is about managing a library of photos. Reader Chris Thomas, in South Australia writes:

My wife and I run separate catalogs in Photoshop Album 2. The photos are held in "Her Pictures" and mine in "His pictures" on XP. Sometimes photos go into the wrong folder and wrong catalog.
Is there a simple way to move photos from one catalog to the other?
Or, do you delete them from the "old" catalog, Move the photos in say "Her Pictures" to "His Pictures" and then import them into the other catalog?

I've never really liked Photoshop Album 2 (and most other photo album products) because they don't handle photo sharing and synchronizing well. For example, I've yet to find an album product that lets me load images off a Compact Flash card onto my laptop and organize them while on a shoot, and then take those organized, catalogued, and annotated images and incorporate them into my master album. I also have yet to find an album product that easily lives through a Windows upgrade and reinstall, keeping track of all the images correctly and easily.

Chris, photo album products are not optimized to work well with multiple catalogs. You might simply try making a single catalog, with different categories for your pictures and those of your wife.

Bit depth in JPEG images

Continuing our international theme, Andrew Daviel in Canada asks:

What is the bit depth (analog converter resolution) of a camera, and what happens to this bit depth when an image is converted to JPEG (or not) and then viewed on a computer monitor or printed?
I notice that when manipulating an image to brighten it, that bright areas start to saturate and the colours get corrupted, due to only having 256 brightness levels. I read somwhere that some cameras have a 12 or 14-bit A/D converter, but as far as I can see JPEG allows only 8-bit (or maybe 12-bit) depth. No idea what my camera has as native depth -- cheaper Kodak which converts to JPEG internally -- but I think I only see 8 bits in the output files.

Nice question. Let's see if I can get close to answering this correctly:

There are literally bajillions of colors out there. JPEG is a compression algorith, so its goal is to always use the least data necessary for presentation. But you are both right and wrong about the 8-bit depth of JPEG.

Typical JPEG images provide 24 bits per pixel, but that's 8-bits per channel (red, green, and blue). If you use a more modern version of Photoshop, you'll notice it will also let you work in 16-bits per channel, which gives you 48 bits per pixel.

Most likely, though, you'll need to save the image as a RAW image (which will be far bigger than your JPEG) and then work with that at the 16 bits per pixel bit depth.