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Plustek OpticFilm 7200 Resolution Tests
Summary
Plustek quote 'Resolution: "hardware optical 7200 x 7200dpi" in the Plustek OpticFilm 7200 specification sheet. When measuring resolution using the USAF1951 T-20 test experimenters found varying results: FilmScanner.Info - 2900dpi; Plustek - 4096dpi; StiftungWarentest - 4100dpi.
USAF1951 Resolving Power Test
The
3-Bar Resolving Power Test Chart was devised in 1951. The resolving
power target consists of a series of 3 line horizontal & vertical bars.
Each of the 3 lines of a bar are separated by spaces of equal width. The
test consists of seven groups (-2, -1, 0, 1, 2, 3, 4) consisting of six elements
(1, 2, 3, 4, 5, 6) which are progressively smaller. If the scanner can still
resolve the three black lines in relation to the white background, then one
can find the associated resolution in Dots Per Inch.
Using some complicated maths gives a table showing pairs of lines per millimeter for each element of each group.
Given that we know the figure for pairs of lines per millimeter how can we convert into DPI (Dots by inch)? 1 inch = 25.4 mm so multiply the above table by 25,4. A further multiplication factor of x2 is necessary, since a pair of lines always by definition consists of two lines. With a conversion factor of 50,4 gives the following table:
It is often difficult to judge whether an element is still resolved or not. The resolution difference between two elements amounts to 12% so you can see that this level of error or more can occur based on the subjectivity of two differant testers.
Highly technical details of the USAF1951 test with more practical information at FilmScanners.info (English translation)
Test Results
Filmscanner.info Tests
Filmscanner.info found OpticFilm 7200 resolution was 2900dpi using the USAF1951 T-20 test (T-20 image test) - they could recognise only Element 6 of Group 5 (5.6). Filmscanner.info said "Bei der Analyse des USAF1951-Scans traute ich jedoch meinen Augen nicht, was ich da sah. Mit viel gutem Willen kann man noch das Element 5.6 erkennen, wobei man gestehen muss, dass sich bei diesem Element die schwarzen Balken vom Hintergrund nicht mehr eindeutig differenzieren lassen wie beim vorigen Element 5.5. Dem Element 5.6 entspricht jedoch gerademal eine Auflösung von 2900 dpi; das sind ja nicht einmal 50% der Nennauflösung." Full Build Quality section (German / English google translation)
Plustek Resolution comments
DataMind asked Plustek to comment on the FilmScanner.info results. Plustek replied saying "With regard to dpi issue, here is the explanation...the scanner has 2 3600-dpi CCDs in stack, hence technically declear 7200dpi. It is more like hardware interpolation. Please refer to attached PDF file, it is from StiftungWarentest, one of the most serious testing agencies in Germany. In the last page you can see the testing result of 7200, they say the result is 4100 dpi. The testing chart they use, is USAF 1951 T20 chart. We have one at hand and made tests, I would say the result reaches no less than 4000 dpi. Having said that, I will have to say that, the quality may be vary, however there won't be dramatically differences."
Plustek Tests
Erich Huang at Plustek tested OpticFilm 7200 using the USAF1951 T-20 test. Scanning at 7200dpi setting Plustek got a result of 4096dpi - Plustek T-20 Test Result psd file, jpg file. "As you can see, up to Element 3 of Group 6 can be recognized (6.3). In plain words, this is 80.63 line in pair/millimeter, which can be converted to 4096 dpi. That's why I claimed 4100 dpi. With regard to USAF 1951 chart info, please refer to... efg2.com and filmscanner.info Aufloesung."
StiftungWarentest Tests
With Plustek OpticFilm 7200 the German testing organisation StiftungWarentest found a 4100dpi resolution result using the USAF1951 T-20 test - see last paragraph on page 6. For an (rather poor) English google translation click here.
Results Compared
DataMind cropped the T-20 results to leave Groups 4, 5, 6 & 7 and magnified both results by 200% so that you can clearly see the heart of this matter.
With the FilmScanner.info Test - you can see the white gaps between the bars in 5.6 (green arrow) which corresponds to a 2900dpi resolution but not 6.1 (red arrow) .
With the Plustek Test - you can see the white gaps between the bars in 6.3 (green arrow) which corresponds to a 4096dpi resolution but not 6.4 (red arrow).
At 2900dpi the FilmScanner.Info resolution result is 30% lower than the 4100dpi Plustek & StiftungWarentest results.
NB. If the scanner had 7200dpi resolution - one would expect the result to be 7.2
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| FilmScanner.info Test: 5.6 = 2900dpi | Plustek Test: 6.3 = 4096dpi |
7200i SE tests by ColorFoto
Tested: 2800ppi May 2006 (full Article, jpg)
