Low quality image when adding to iMovie

Question

I have 2 movies that I want to remove some parts, but when adding to iMovie, it changed some video adjustments to a worst quality image.
This 2 movies had already bad image quality from the source, because they have very darkness frames and were filmed in VHS.
But they were reasonable to see, from Apple TV.
Now in iMovie they became worst.
The source is H.264, AAC 1280x720 FPS 23,97
The source is H.264, AAC 1024x576 FPS 23,97
What can I do ?

Answer 1

Available ?
More or less.
And how can I send a sample ?
Depends on the size of the sample and what space is available to you on a server. You can usually send snippets as e-email attachments up to about 10 MBs. If you have a MobileMe account, server space provided by your ISP, or other server space provided by a third-party service, then you can upload larger samples for FTP or webpage use and simply post/send me the URL, reference movie, or QTL.
When the movie goes to iMovie, the brightness decreases and the contrasts became more darkness.
Have you tried playing with the built-in "Video Adjustments" at all? Not the easiest thing to use but you can make some adjustments using it. In such work, "Less is usually best." By this I mean you should apply as little adjustment as you can get away with using.
Normally I would start with a "Level" adjustment. While there is an "Auto" button you can press to get some idea as to what the application says you need for a particular frame or range of frames, this setting can vary drastically depending on the individual frame being tested. So it would usually be a good idea to expand your clip and "test" a number of frame ranges to see what is a "typical" setting for the clip. If the settings are fairly uniform, you can go with the suggested setting or something reasonably close to save "blowing out" highlights. On the other hand, if the settings vary drastically, you my either wish to select an "in-between" setting of your own manually, or split the clip into sub-segments which can then be adjusted individually. NOTE: the auto "Level" adjustment does not affect other settings -- only the clipping points and does not include controls for half or quarter tone adjustments. Still it is my preferred starting point for making adjustments.
You can also try adjust the "Exposure" setting. This will tend to allow you to adjust the "Brightness" and "Contrast" uniformly by centering your color channel histogram but can easily be overdriven. "Brightness" and "Contrast" can, of course, be adjusted individually if you prefer but you may find the "Exposure" control easier to handle where the content is more uniform with regard to shadows and highlights. Lastly, adjustment of any of the previously mentioned controls will usually have some effect on color saturation. While they do not change the actual setting, they do tend to desaturate color as the other controls "lighten" the cast of your frame images. So, don't be surprised if the results "wash out" somewhat and you may need to touch up the saturation. But, once again, go easy as the saturation doe not increase uniformly and tends to "blotch" highlights and/or create color shifts in these areas.
About the only controls left are the individual color channel levels. I don't normally recommend playing with these arbitrarily as they then to shift the color cast/white balance of your content. As to the White balance itself, the "eyedropper" had little or no effect on the content I tested so I assume the it either did not work as described or the sample white/grey points I used for sampling did not require adjustment. As to the Balance Wheel," it does work well but like the color channel adjustments may cause more harm than help most novice users.