EXIF MetaData

[hanji]

Hello All

I wanted to create a new thread about EXIF MetaData. I think this could be really useful information to help analyze photographs (digital only). During an investigation or if a unusual anomoly is caught during a photo shoot for instance, it's extremely easy to not be aware of how the picture was actually taken. You might not know with 100% certainty what setting it was at. You might know the circumstances of when the image was taken, but physical factors of the camera itself are lost.

EXIF stands for Exchangeable Image File. This is the native format that most digital camera actually uses to store the image. It will then convert the image (or compress it) to be a JPEG image. JPEG is a compression mode. This how you end up with a .JPG or .JPEG file in the end. Some cameras will use a non-compressed format which is .TIFF. When a camera takes a picture it will create a small header file attached to the image itself. This is called the EXIF MetaData. This information contains various bits of information about the moment the image was taken from the camera's point of view. It will store date/time, various settings, exposure, etc with each file. Each make/model of digital camera will have different values and may include or exclude certain pieces of information, but the basics should be available for all digital cameras.

To view EXIF data, the simplest method is to view the Property of the image. Going to Windows Explorer, browse to where the image is. Right click on the image and select properties. From there, click the 'Summary' tab. The information presented will be the basic set EXIF MetaData.



Based off of this earlier thread, I wanted to get a rough definition for some of the terms. Some of these could be wrong, but I did consult with a two photographers:

Artist
It is possible to embed watermark information containing Artist and Copyright information
Copyright
It is possible to embed watermark information containing Artist and Copyright information
Make OLYMPUS OPTICAL CO.,LTD
Make of the camera
Model X-2,C-50Z
Model of the camera
X resolution 144
Horizontal resolution. This is saying that it's 144dpi resolution
Y resolution 144
Vertical resolution. This is saying that it's 144dpi resolution
Software Adobe Photoshop 7.0
This indicates that it was edited with Photoshop 7.0 at some time
Datetime 2007:04:20 19:21:55
This indicates the date/time of the image BUT Photoshop has a nasty habit of overwriting the timestamp
YCbCr positioning co-sited
Unknown
Exposure time 4 s
This is the shutter speed. The shutter on the camera was left open for four seconds. The slower the shutter, the more light that is let in. To avoid blurring go with a fast shutter speed 1/250, 1/500, 1/1000 of a second. Anything shutter speed longer than 1/60 or 1/30 or a second tends to start blurring. Things like body movement show up in the picure (soft focus)
F-number 2.8
I'm guessing this is the f-stop. Looks like an f-stop value. Besides the shutter, this is the other way to control exposure on the camera. This is a way of measuring the size of the aperature opening on a lens. The higher the number, say f-16, the less light you are letting into the camera through the lens. The lower the number the more light you are letting in. If you want good depth of field, i.e. more things in focus in the picture, foreground, background etc, you accomplish this by "stopping down the lens", closing the aperature down. An f-stop reading of 16 gives you good depth of field, whereas 2.8 would give you shallow depth of field. This means subject matter is in focus, but background is out of focus etc. Sometime you hear the term fast lens, this means it can usually go down to a f-stop of 1.0. This lets in more light and gives giving one a really shallow depth of field.
ISO speed ratings 80
This is your film exposure rating. Normal everday film that you would use out in daylight is around 80-100. 400 is for less light. Super fast film (for lowlight shooting is around 3200. The lower the iso rating, the less grainy the film will be. The higher, the more grain you get.
Date/time original 0000:00:00 00:00:00
Depending on the camera model, this will be updated
Date/time digitized 0000:00:00 00:00:00
Depending on the camera model, this will be updated
Component config YCbCr
Unknown
Exposure bias value 0
Exposure compensation. This is a way of adjusting for flaws inherent in the light meter of your camera. If you are shooting a lot of white objects in the sun, the light meter is going to read a lot more light coming off the object than is really being reflected. You would set your exposure bias (exposure compensation) to a negative number (measured in +/- EV), to make up for this extra light and to ensure that you get a proper meter reading. Black object would require you to go the opposite and set your EV to a positive number to compensate. A quick example is a normal White dude puts off about one stop less light than a meter reads. The meter gives you a false high reading and your picture is one stop too dark. So if I meter off my hand and the light meter tells me that a good exposure would be shutterspeed 1/125 and f-stop 4.0, i'm going to want to adjust one stop. I can do that by letting in less light by switching the shutterspeed to 1/250 and leaving the f-stop at 4.0, or I could leave the shutterspeed the same and and open up the aperture to 2.8. Probably best to just compensate for this manually.
Max. aperture value 3
Max aperture refers to how far the lens opens up (low end of the aperture settings, 2.8, 2.0 etc). Above we get an f-number of 2.8 which lets in more light than 3. So I'm a bit confused as to why the max reading value is 3 and not 2.8
Metering mode Pattern
Metering mode Pattern not sure what exactly the metering mode pattern is, but traditional light meters and cameras have a few different ways they can figure out the right exposure for a picture. A spot meter usually only reads light from a small circular area in the middle of the lens. Good for finding the exposure of specific objects in the frame, i.e a face. The draw back is the picture will only be properly exposed for what you metered off of (the background might lose all detail because it is too dark, but the face will look properly exposed). Other kinds of meter settings try to take the foreground and background into account sort of averaging out the exposure so everything in the frame is somewhat well exposed.
Light source Unknown
Not sure what value could be provided here.
Flash Yes
If flash was on or off for the shot
Focal length 7.8 mm
I think the distance between the glass elements in the lens when focuses on a subject, but not 100% sure.

Any information we can gather about a photo can include valuable data to help anaylze the particular settings to capture that shot. Also the ability to compare separate photographs, or separate cameras during the same location or timeline. Another aspect is to possibly detect fraudulant or altered evidence. This cannot be solely used to to verify validity since EXIF MetaData can be altered as well, but could be used as part of the analysis process.

hanji

[monte_9501]

That is way cool I had no idea that was on there, Not to late to teach an old dog new tricks

[Smokey]

You are correct in your info. The cool thing is that if your camera has the date saved you will not get overwrite from Photoshop. All 3 date/time stamps are saved from the date and time of photo. If you don't have date/time or have not set it, you will get the stamp of when the image was loaded on the computer.

[pythons69]

my windows vista options are a little different but its all still there but anyway I never knew that info was attatched to a pic like that what other computer magic are you gonna teach us?

[Kris]

Yeah I got Vista aswell and it's a tad diff. but all still there.

[hanji]

pythons69 Wrote:my windows vista options are a little different but its all still there but anyway I never knew that info was attatched to a pic like that what other computer magic are you gonna teach us?

Doh! I need to get a Vista machine set up for testing. I always forget that. Glad you got it to work. Like I said this is the 'lite' version of EXIF.. you can extract even more with a programming scripting language.. but that's just more nerd talk.. so don't get me started... heh!

Thanks!
hanji

[pythons69]

even fixing trucks these days requires nerd talk everything on a semi is computer controlled now..... even the lights and radio

[Smokey]

I used Adobe Photoshop.