Brain teaser #2: Converting between gamma and ev

PE
Posted By
phoney.email
Oct 25, 2003
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490
Replies
4
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Closed
Does anybody happen to know the relationship between gamma and ev,
i.e. how does gamma map to ev, or vice versa?

In other words, how would one express gamma as ev values (or "verse vica")?

I’m looking for an answer along the lines of: "x.x gamma equals +/-y.y ev".

In case the relationship is not linear, then either a formula or a table of values between, say, -2 ev to +2 in .1 increments would do.

Thanks very much as always.

Don.

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M
mitch
Oct 28, 2003
"Don" wrote in message
Does anybody happen to know the relationship between gamma and ev,
i.e. how does gamma map to ev, or vice versa?

In other words, how would one express gamma as ev values (or "verse vica")?

I’m looking for an answer along the lines of: "x.x gamma equals +/-y.y ev".

In case the relationship is not linear, then either a formula or a table of values between, say, -2 ev to +2 in .1 increments would do.
Thanks very much as always.

Don.

I’m a bit of an interloper here, so please forgive me if I’m out of line with this.

This discussion might help you with EV.
http://medfmt.8k.com/mf/ev.html
and further http://en.wikipedia.org/wiki/User:Egil/Sandbox

I think asking the relationship of gamma to ev is like asking how far west is the north pole.
As I understand it gamma is dimensionless – a characteristic of a system processing pixels.
EV on the other hand is related to the an amount of light. The above links include discussion of the relationship to the illuminance of an image taking into account the film camera characteristics. For digicams, the storage characteristics would need to be considered as well as that of the sensor array.
PE
phoney.email
Oct 29, 2003
On Tue, 28 Oct 2003 22:50:02 +1000, "mitch"
wrote:

"Don" wrote in message
Does anybody happen to know the relationship between gamma and ev,
i.e. how does gamma map to ev, or vice versa?

In other words, how would one express gamma as ev values (or "verse vica")?

I’m looking for an answer along the lines of: "x.x gamma equals +/-y.y ev".

In case the relationship is not linear, then either a formula or a table of values between, say, -2 ev to +2 in .1 increments would do.
Thanks very much as always.

Don.

I’m a bit of an interloper here, so please forgive me if I’m out of line with this.

Oh no, not at all. On the contrary: Interlop away! ;o)
All help is most welcome.

This discussion might help you with EV.
http://medfmt.8k.com/mf/ev.html
and further http://en.wikipedia.org/wiki/User:Egil/Sandbox

I’m familiar with EV, it’s gamma I wasn’t quite clear on. However, I just got a very concise and clear explanation over in
comp.periphs.scanners.

I think asking the relationship of gamma to ev is like asking how far west is the north pole.
As I understand it gamma is dimensionless – a characteristic of a system processing pixels.
EV on the other hand is related to the an amount of light. The above links include discussion of the relationship to the illuminance of an image taking into account the film camera characteristics. For digicams, the storage characteristics would need to be considered as well as that of the sensor array.

Superficially, both Gamma and EV "make the picture brighter". Now, that’s a very tenuous connection, granted, and I was quite aware it may sound very silly, but I had a hidden agenda…

I was intending to use this to set analog gain of the scanner based on adjustments made to a test image in Photoshop. The idea was to convert image settings (after correction in PS) to analog gain (which = EV) and so make corrections at the earliest stage in the scanning process to avoid cumulative errors and before the image is downsampled and therefore downgraded (both in terms of bit depth and subsequent "soft" adjustments).

Anyway, it was just an idea. No harm in asking, as they say…

Don.
D
drjohnruss
Oct 30, 2003
"Don" wrote in message
Does anybody happen to know the relationship between gamma and ev,

check out the Reindeer Graphics Optipix plugins. the contrast adjustment functions are calibrated in both gamma, EV, and the photographer’s zone system. <http://ReindeerGraphics.com>
PE
phoney.email
Oct 30, 2003
On 30 Oct 2003 00:35:13 GMT, (DrJohnRuss) wrote:

"Don" wrote in message
Does anybody happen to know the relationship between gamma and ev,

check out the Reindeer Graphics Optipix plugins. the contrast adjustment functions are calibrated in both gamma, EV, and the photographer’s zone system. <http://ReindeerGraphics.com>

Thanks! Will do.

Don.

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