How do you do screenshot comparisons?

[krackato]

I was using PowerDVD 4. I used to pause the movie and then hit the next button. At the next chapter, it would remain paused and I could take a screenshot. I would do this with movies when I was using Instant Copy or DVD95copy or DVDshrink or whatever and compare the compressed screenshot to the original screenshot.

However, I've noticed that since upgrading to PowerDVD 5, when I hit pause, then the next button, it simply starts playing the next chapter. Which got me wondering, how do you guys do your screenshot comparisons?

Also, I've got some screenshots comparisons for Old School and Femme Fatale between the Original, Instant Copy and DVDshrink if anyone is interested in hosting them.

[SirCentipede]

I used to do it with WinDVD, but nowadays i use virtualdub. For comparing transcoders see this thread:

http://forum.doom9.org/showthread.php?threadid=58808

[JFerguson]

krackato,

I use your same method with PowerDVD 4. I have not played with v5 yet, that's interesting.

I actually recorded a little macro using Windows 3.1 RECORDER.EXE (it still runs somewhat on all the new versions of Windows) that clicks the chapter advance button, then clicks the snapshot button.

Yeah, I'm lazy; but I'm not avid mouse user.

I have tried the VirtualDub method that SirCentipede refers to (originally documented my quantum, I believe). I suppose it has its place, but in testing, PowerDVD 4 produced the same samples and resulting analysis as did VirtualDub.

That is, I took snapshots from PowerDVD for a DVD Shrink transcoding (at low 10% compression). Most of them were bitwise identical to the original. I loaded the same frames in VirtualDub, did a PASTE from source video, did a COPY in Paint Shop Pro v6, and saved as bitmap. They too were bitwise identical to the original, and therefore bitwise identical to the ones taken from PowerDVD.

At lower compression, upon examination, I see the same video anomalies from PowerDVD snapshots as I do with comparisons in VirtualDub.

So, I prefer to use PowerDVD, since with my macro, I can produce 30 samples in about 15 seconds. Then I load them into ACDSee Classic, do a slideshow, Zoom in lock, set the slideshow timer to infinity, then page up/down between the snapshots. Very effective. With VirtualDub, the Alt-Tab transition between instances is just too noisy. ACDSee classic will only zoom lock the upper left corner of the frame which is alright for most cases. If I need better control over the zoom portion, I'll load them into Paint Shop Pro 6, zoom to wherever, and control-tab between snapshots.

I have been doing some comparisons as you have. The results are interesting. In a lot of cases, DVD Shrink beats InstantCopy at low compression. But the tides turn, as you start hitting 20% and beyond. I will post some samples soon.

In the meantime, I don't have the link with me now, but look for a recent post by me. It has some links to some snapshots that I hosted on a free image host provider. You'll have to save your snapshots as JPEGs, but those will work fine...

[krackato]

Well, I was hoping to install PowerDVD 4 and 5 on the same computer, but it seems the installer will only let me have one installed at one time. I've gone back to PowerDVD 4 since I rarely watch movies on my computer anyway and the screenshot thing was a big deal for me, but does anyone have any idea how I could run both on the same system.

Very cool idea about the Macro, JFerguson. I might have to look into making one myself.