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Digital Images - EXIF data explained


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#1 CaveRat2

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Posted 16 July 2011 - 09:19 PM

EXIF file stands for Exchengable Image Format file. It is a series of data placed on a digital image by the camera when the image is made. An example of one such file follows with an explanation of a few key points;

JFIF_APP1 : Exif
Main Information
Make : Canon
Model : Canon PowerShot SX100 IS
Orientation : left-hand side
XResolution : 180/1
YResolution : 180/1
ResolutionUnit : Inch
DateTime : 2010:06:15 22:17:44
YCbCrPositioning : centered
ExifInfoOffset : 196
Sub Information
ExposureTime : 1/60Sec
FNumber : F4.3
ISOSpeedRatings : 250
ExifVersion : 0220
DateTimeOriginal : 2010:06:15 22:17:44
DateTimeDigitized : 2010:06:15 22:17:44
ComponentConfiguration : YCbCr
CompressedBitsPerPixel : 3/1 (bit/pixel)
ShutterSpeedValue : 1/60Sec
ApertureValue : F4.3
ExposureBiasValue : EV0.0
MaxApertureValue : F4.3
MeteringMode : Division
Flash : Fired
FocalLength : 60.00(mm)
MakerNote : Canon Format : 2408Bytes (Offset:690)
UserComment :
FlashPixVersion : 0100
ColorSpace : sRGB
ExifImageWidth : 3264
ExifImageHeight : 2448
ExifInteroperabilityOffset : 3362
FocalPlaneXResolution : 4110222/225
FocalPlaneYResolution : 3082666/169
FocalPlaneResolutionUnit : Meter
SensingMethod : OneChipColorArea sensor
FileSource : DSC
CustomRendered : Normal process
ExposureMode : Auto
WhiteBalance : Auto
DigitalZoomRatio : 3264/2592
SceneCaptureType : Standard
Vendor Original Information
MacroMode : Off
Self-timer : Off
Quality : Fine
FlashMode : Forced activation
Drive Mode : Single-frame
Focus Mode : Single
ImageSize : Large
Easy shooting mode : Manual
Digital Zoom : On
Contrast : Normal
Saturation : Normal
Sharpness : Normal
CCD Sensitivity : AUTO
MeteringMode : Evaluative
FocusType : Auto
AF point selected : Unknown (8197)
ExposureProgram : Aperture Priority
Focal length of lens : 6-60(mm)
Long Shutter Mode : Off
White Balance : Auto
Sequence number(Continuous mode) : 0
Flash bias : 0 EV
Image type : IMG:PowerShotSX100ISJPEG
Firmware version : FirmwareVersion1.00
Image Number : 1000730
Owner name :

I won't explain all of these,it would be too involved, but instead will mention a few important ones related to the picture this was taken from and what they tell me.


Make : Canon
Model : Canon PowerShot SX100 IS
This is the make and model of the camera that made the image, a Canon SX100

Orientation : left-hand side
XResolution : 180/1
YResolution : 180/1
ResolutionUnit : Inch
Resolution data for ths image Higher numbers equal more detail in the picture. Settings are controlled by the photographer and the resolution setting on the camera.

DateTime : 2010:06:15 22:17:44
Date and time the image was made. (Provided the date is set correctly by the user on the camera.)

ExposureTime : 1/60Sec
FNumber : F4.3
ISOSpeedRatings : 250
These are the important ones. They tell the shutter speed, aperature setting, and equivalent ISO setting used for this image. If it was an auto exposre then they will convey the setting selected by the camera to make the image.

CompressedBitsPerPixel : 3/1 (bit/pixel)
Amount of digital compression used on this image. Too high and the image quality may suffer.


Flash : Fired
Indicates flash was fired for this image.


ExposureMode : Auto
Indicates that this image was made in the auto mode rather than a manual setting.

MacroMode : Off
Self-timer : Off
Macro mode and self timer were not used in making this image. If they had been these would indicated as On

Quality : Fine
Tells me the quality setting used. For this camera "Fine" is the mid-level setting for resolution.

FlashMode : Forced activation
Flash was forced, that is even had there been sufficient light the flash would have fired regardless.

Drive Mode : Single-frame
Focus Mode : Single
ImageSize : Large
Easy shooting mode : Manual
Digital Zoom : On
Contrast : Normal
Saturation : Normal
Sharpness : Normal
CCD Sensitivity : AUTO
MeteringMode : Evaluative
FocusType : Auto
A series of settings most unique to this camera. Some are self explanatory, others would be explained better by the camera user's manual.

ExposureProgram : Aperture Priority
This image was made with aperture priority instead of shutter priority. Either will determine the overall exposure, one controlling the amount of light( aperture), the second by how long the light was present (shutter).

Focal length of lens : 6-60(mm)
Long Shutter Mode : Off

The exact terminology may vary between cameras, but this gives a basic look at the type of data the EXIF provides. One can see from this why such information is vital if one is to analyze a digital image.

#2 coredump

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Posted 19 July 2011 - 07:51 AM

Good information CaveRat.

There are many free programs available that will display the EXIF metadata for digital images. One that I like is "JPEGsnoop".

Not only will JPEGsnoop display EXIF metadata, JPEGsnoop contains a database that compares an image against a large number of compression signatures. JPEGsnoop reports what digital camera or software was likely used to generate the image, so it's helpful when trying to determine if an image has been "Photoshop-ed".

JPEGsnoop is also opensource if you want to dig into the code and see how things work.

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#3 CaveRat2

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Posted 19 July 2011 - 09:02 AM

Good information CaveRat.

There are many free programs available that will display the EXIF metadata for digital images. One that I like is "JPEGsnoop".

Not only will JPEGsnoop display EXIF metadata, JPEGsnoop contains a database that compares an image against a large number of compression signatures. JPEGsnoop reports what digital camera or software was likely used to generate the image, so it's helpful when trying to determine if an image has been "Photoshop-ed".

JPEGsnoop is also opensource if you want to dig into the code and see how things work.

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I used a simple EXIF viewer program, also free. I did download JPEGsnoop jusy now, it looks good and I will have to take some time to play around with it. The additional database does provide another way to examine pictures, and anything we can do to make spotting hoaxes easier certainly is good news.

#4 freyjasdottir

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Posted 19 July 2011 - 08:06 PM

I might download that as well, new laptop means I can visit here more and have more goodies to play with.
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#5 OMPRDave

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Posted 23 July 2011 - 12:47 AM

Pretty useless...ghost photos are, from what I've seen the last ten years, solved for the most part. Not hard to spot a fraud on the first look. I'm not out to expose anyone else's pics...I just don;t look at them more than once.
"There is a principle which is a bar against all information, which is proof against all arguments and which cannot fail to keep a man in everlasting ignorance - that principle is contempt prior to investigation." Herbert Spencer

#6 WeirdFresno

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Posted 24 July 2011 - 11:06 PM

It may be easy to spot a fraud, but being able to prove that is nice. I've received photos in the past that were obvious fakes (someone used the airbrush tool in Photoshop to populate the photo with orbs), but upon opening the EXIF data and seeing it was edited I asked for the original photo (I mentioned that it was edited in PS and said I assumed it was cropped or something) and never heard back from the person.

Plus it's nice to know when the flash fired. I've had some strange photos in the past and wasn't sure what caused it. There were reflective surfaces but I was sure the flash didn't go off. Checked the EXIF data and I was wrong. So the info can have it's uses outside of trying to verify if something has been altered or not.




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