TTG Plus > FAQs > This is FAQ 14
On P4 of the Trust Test
“One scene”
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1401. What’s the point of P4?
P4 ensures that all TTG-qualified photos depict only one scene even when there is change in the scene or change in the lighting during exposure.
P4 actually does four things
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1402. So changes in the scene or lighting are the issue for P4?
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1403. And the four requirements in the last paragraph of P4 are there to prevent “disqualifying visual effects”?
Yes. Without all four of those requirements, it would be easy to make photographs that fail to meet A, B, C, or D in #1401.
More on #1403
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1404. Does P4 always disqualify smartphone “group” (or “couple”) photos that pull the best expressions or poses from different exposures into one picture?
Yes, such pictures are always disqualified from TTG, because the result depicts as simultaneous a combination of visual elements (that is, a scene) that did not occur simultaneously in real life.
In other words, the picture does not show a specific appearance that occurred during exposure (“satode”)—
—and thus it is always disqualified both by P4 and by P7.
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1405. Is using Auto exposure settings the best way to meet P4?
Yes; most photographers will not have trouble meeting P4 when they use automatic settings and semiautomatic settings (i.e., aperture- or shutter-priority) on their smartphones and cameras in normal light.
But there are exceptions in difficult lighting conditions
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1406. So manually choosing exposure settings is more likely to cause issues with P4?
Yes — but in practice, most photographers who are advanced enough to manually select their exposure settings will usually understand the four requirements in the last paragraph of P4 and can knowledgeably consider their options.
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1407. If TTG photos can only depict “one scene,” why does TTG allow at all for combining multiple exposures?
Because many millions of non-deceptive photos are made every day on smartphones that instantly combine multiple exposures to improve picture quality.
More
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1408. Does the “ghost objects” prohibition of P4 disqualify what is traditionally considered a “double exposure” of the kind made in the 19th and 20th centuries?
Yes it does (assuming the reference is to having semi-transparent scenes overlap in the same photograph).
More
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1409. Why doesn’t motion blur disqualify photos from TTG?
Because genuine motion blur is very familiar to the public and is not considered deceptive.
More
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1410. What about the use of flash during a single exposure, which often illuminates the scene for only a fraction of the total exposure?
Normal use of a single flash is usually not a disqualifier from TTG; see the guide to flash photography.
See also the “P4” tab on “How undoctored photographs work”
The numbering of the FAQ questions will not change — any new questions are added at the bottom and given new numbers — so users can safely make a link to any specific question.