So... I finally come to a decision to go with the OM-D... Is there any big hand users out there?

Started Mar 13, 2013 | Questions thread
Martin.au
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Re: Issue 2: How to fairly compare output image IQ of two similar DSCs
In reply to Jack Hogan, Mar 17, 2013

Jack Hogan wrote:

Mjankor wrote:

Jack Hogan wrote:

Mjankor wrote:

Quote from Jack Hogan:

"Camera manufacturers can define ISO (S) as they please thanks to a lax standard. Because of this fact it is not possible to measure the performance of camera A at a set in-camera ISO (let's call itSubjective S) and expect to meaningfully compare its results to those from Camera B at the same ISO setting."

Sure looks like you claiming that there is "Inconsistent in-camera ISO labelling by manufacturers."

Indeed. Does the rain fall down or up? Just look the next time you are out

Now give an example of one, because from what I've seen all cameras stick pretty close to the ISO 12232:2006 standard.

Which one? There are 5 ways that the standard allows manufacturers to define ISO. One of the five (enphasis added):

"The Recommended Exposure Index (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model’s Exposure Index choices arbitrarily. The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings."

Did I mention that most often than not they determine ISO on the basis of a fully rendered sRGB image, after camera and vendor specific subjective curves and profiles have been applied?

The sky is the limit.

As the purpose of a camera is to create photos and as a function of generating these photos is the application of curves and profiles, this seems entirely appropriate to consider.

Now, you may claim that how that ISO relates to DXO's ISO is arbitrary, as it is, but that's not a problem. Instead, as DXO have said:

"In fact, it is precisely the JPEG ISO value that all the manufacturers publish. They do so because JPEG (or any RGB) output is the visible output that photographers use. So when you select ISO 800 on your camera, you’ll have a JPEG ISO at 800, but the RAW ISO will be at (for instance) 550. The JPEG results are achieved by playing with the tone curve shape. This is absolutely legitimate: the ISO standard allows manufacturers to use this JPEG value. They are not cheating."

This manufacturers ISO is definitely not arbitrary, and cameras stick pretty closely to it.

I never said that it was illegittimate or that they were cheating. The conspiracy theory simply muddlles the subject and makes it harder to see that in-camera ISO labelling is inconsistent from camera to camera and from manufacturer to manufacturer. Which makes comparing apples-to-apples harder to do for people who do not know what they are doing.

Jack

I'm not going to go into the standard now. I don't have time to research it, and I think you're supposed to be the expert.

However, a result of the standard is that if you can test the manufacturers reported ISOs against the standard. and also against each other. (As DPReview does)

More importantly, what the standard means is that two cameras, with similar exposures, and the same camera ISO settings, should result in an equally bright jpeg (or raw through most raw converters).

While the process of getting to the final image can be arbitrary, the results are absolutely not arbitrary. Exposure + camera ISO = an equally bright final image.

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