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I have a problem with images that are too bright.

See image. On the right, nice well-toned miniDV image, on left a nasty, way 'over-exposed' PVR (a Mobibox clone from RC Tech) image. Both recorders were recording from the same feed via a video splitter. .

After reading this forum I'd hoped that getting a video splitter with adjustable outputs would help, but it doesn't; if you crank the output level down, a fraction of a second later both recorders will crank the level back up with their internal AGCs. Not a problem with the miniDV, but the PVR is clearly 'factory set' to too high a level. This becomes clearer when you attempt post-processing: there's just nothing there at the top end of the image, it's saturated.

Now I can accept that miniDV makes a better job of compressing & recording the image, but this is clearly a case of the PVR screwing things up before the compression/recording stage.

So, if I'm going to use the PVR at all:

- is there something apart from absolute signal level that might be adjusted to fool the RC Tech PVR into recording things darker?

- anyone fiddle about inside one of these? Any hacks one can apply to the internals of the PVR to correct this?

Or do I just have to warn folks about this particular recorder and move on?

(Kilrah - I had no reply from RC-Tech about this problem, which is not characteristic).

post-5-1181396427_thumb.jpg

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(oops, on closer examination, I see those aren't exactly the same frames! Here's the miniDV frame that matches the PVR one more closely)

post-5-1181396687_thumb.jpg

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It's indeed a known and unidentified problem... I usually advise to compensate for that when editing, apart from the really saturated zones you can get something decent.

The splitter apparently only has a pretty short adjustment range - too short for that. You can try adding a voltage divider in line with the video cable (500Ohm - 5k, use a 5k6 pot if you have one), that will lower the level enough to avoid saturating the image, which will then look a bit dynamically compressed but unlike saturated zones that can be totally corrected with a brightness/contrast filter when editing.

There's no hope in modifying the guts, at first that could have looked like a lack of 75Ohm termination, but it is here, so that's ruled out. My guess would be a software parameter that programs the video acquisition chip badly, and could explain why some brands under which these things are sold work, and some not. Apparently, of course there's no more way to get those that worked, discontinued. I wanted to try flashing the software from another brand to check, but never found one... :(

Regarding answer - there's no trace of an email from you in the inbox :unsure:

post-5-1181400019_thumb.jpg

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if a video feed is too bright it might be the reason it is not loaded with 75 Ohm,

try to add different resistors to the feed that is too bright, and see if this helps,

start with 100-82-75-50 one og them might help you

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PVR=pocket video recorder, little MP3 and video player/recorder that stores on flash memory

Thomas, as I said I checked for the 75Ohm termination and it is OK.

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(My apologies to Kilrah - I should have re-sent my email before coming to this board)

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Good news! Update - by use of a crowbar, things are looking better. The murky, blurrier image is from the MPEG4 recorder, the clearer one from miniDV, but note that the brightness is much closer now! Interesting that the MPEG4 still ignores those clouds top right, but at least this is now usable.

The 'crowbar' I used was a 100 ohm variable resistor on the video splitter output. Setting minimum level out (~0.5v into 75 ohms), I put this across a 100 ohm trimmer, and took the output from the wiper & earth. At about 40 ohms wiper-earth, the picture looks like this i.e. okay - so the AGC on the MPEG4 input isn't impossible to defeat!

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Oops. Pics attached this time...

post-5-1182619965_thumb.jpg

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i got that PVR/PMP too, and it's not as good as i thought,

mpeg4 compression is better than mpeg2 in low bitrates, but as you can see, final image don0t got enought quality to call it quality,

color is desaturated, and all image become blurry in definition.

if someone want it bcos it's very tiny and portable and just want record videos without having to carry "big" a big minidv or a laptop, then you buy it, but obviously is not the best option,

the real manufacture who do that pmp is axisoft, axisoft.com.

the problem i got in my PVR is that... : when i record videos from the video-out of my dvd, the image i see on PVR is the same is the same that i see when i play the recorded video in the pvr,

but when i record from the receiver of the microcamera i see in the screen a "

good image when recording, but when i play the recorded video it become very pixeled and contrasted,

i don't understand why when the source is the dvd, the recorded image quality is "good", but when i record from the microcam receiver it become very bad,

i can't understand the reason about that.

any idea? (is a cheap camera from ebay i bought time ago, im not doing FPV yet)

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Because aerial images we're used to take have a lot of movement compared to any other source, and that "strains" the codecs enough to reduce quality. I've been asked why my latest easyglider video was looking so good even when it is encoded at a low bitrate, the reason is the same, the images are especially calm.

Codecs are improved for typical video images where most of the scene is stationary or low movement and only the subject is moving more. In our applications all the image is constantly changing and that quickly outgrows the capabilities of those little hardware devices that have to process images in real-time as well as they can. That's why I record using DV, which has no time component in the compression (i.e each image is compressed on its own without considering previous/next ones like most other current codecs), so quality is independent on the content. Then, I leave the hard job of encoding the edited result properly to the PC, as unlike the DVR it can take its time to do that, and require 5 times the duration of the video to do it well if it needs it.

Edited by Kilrah

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but that's not the problem, i recorded videos from dvd's that got quikly images changes, and all fine when recording,

but when i record with the microcamera, seems like it's recording nice, but when i play the recorded video i see its pixeled and got low quality,

i dont do fpv yet so the image is almost static with the camera in my hand just recording a table... my room... there are not quikly movements,

that problem for me is incomprehensible

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It could be a bad video level on the RX or TX. Is the image brightness OK?

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yes image brightness is okey,

as usually you can see in the tft what you are recording, and when i record dvd, the image shown when recording is the same i see when i play the recorded file (well but with a little bit of lost for mpeg4 compression)

but when recording thru the video receiver, the preview image (while recording) is okey, but when i playu the file it become a little pixeled and without the same definition,

is like it record in "low quality" option,

but always is on "Best quality" option !

so i can't understand why the recorded video is so bad when using the camera...

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Interesting... What might be going on here is that the DVDs you are recording are, of course, MPEG2 encoded already - a lot of subtle degradation that passes unnoticed. Clever (if processor-intensive) codec that MPEG2 is, it's already simplified (and reduced the bandwidth requirements to render) the datastream, but in a way that the eye-brain system doesn't easily notice. The MPEG4 codec used by the MPEG4 encoder probably uses a lot of similar algorithms, and thus can easily encode and decode video that looks pretty similar - the original MPEG2 encoding having done the hard work.

The video camera output has had none of this (cpu-intensive) "pre-processing", the (cpu-light) MPEG4 codec has to do all the work, and makes a worse job of it.

MPEG2 remains (from a snob's perspective) pretty poor, mind - explosions or flames still pixelate, and I often notice what on the original, terrestrial broadcasts were full-screen pans (- common in FPV) are broken up into a series of short segments with jumps in between. Transcriptions of cartoons also suffer from this - but you only notice if you're familiar with the (uncompressed) cinema or VHS original.

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well what u xplain got sense,

but the problem seems more complex,

i will try to explain shortly:

when i bought the player i tried to record at best quality obviously from camera, and what i get was a poor quality record,

then i tried to record dvd at full quality mode too, and quality was very poor too, pixeled, and so on.

I then removed battery, format the memory, removed battery and reset all what i could,

then i tried to record from dvd and from camera and in both ways quality was good! quality was the expected one,

and now, don't know why, but i get good quality when recording from dvd, but bad quality when recording from camera,

how to explain that? no way... i can't.

something interesting too is that now,

recording 1 min from dvd, video file size is 7,2 mb, and quality is good as i said,

and 33 secondos from camera, video file becomes 11 mb ! and quality is pixeled and nasty, no quality at all, is as i had selected the "low quality recording mode"

incomprehensible at all, i will become sick, there must be some explanation, but i don't find it,

i write to the manufactured but they don't send me the new firmware,

sorry about by poor and broken english level,

Edited by wallaguest1

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Doofer i was playing a little with a photo editor,

if you edit the video recorded with a video editor, like vegas video 6.0, or any1 you want, you can improve quality a little bit, you see the difference?

testyo1.th.png

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Thanks Wallaguest1, that's quite impressive post-processing! No doubt we'll all have portable screens & recorders that can do this stuff in realtime in a few years.

I'd like a filter that can pull the LCD display out a bit better. Eagletree show on their website the 'Power Panel' being an LCD with black letters on light metal grey background, but when I queried the 'blue on yellow' display they sent me, they denied ever having 'black on light grey', and suggested the web page images were due to image processing. A bit naughty. Leaves me with characters that are hard enough to read live, let alone trying to decipher looking at recordings.

What you're describing sounds more like the PVR randomly selecting a quality setting, but if that's the case, why is the file size so huge? Very odd, as you say. It's certainly not behaving like mine, which as you can see from my images, is not as good as miniDV, but usable.

Have you tried another SD card, or just recording to the (256MB) internal memory? Perhaps these changes, which may affect the memory access speed, will help. I also recall dire warnings about 'only use a REALLY fast SD card' that came with a 2MB/s MPEG4 camcorder I tried.

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Can you post some example video with the problem?

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today i opened the camera and found a very tiny potentiometer in the camera, (for white balance) now image is much more clear, less noise, and with less interference's,

i tried to record my room and so on, and now image quality become better, not as bad as before, i can see colors and image is not blinking constandly with interferences, sun light help a lot in that shame quality CMOS cameras,

im not sure but i deduct that mpeg4 algoritm works much more badly when noise in image is present,

there was what seems to be a exxtremly little potenciommetter in the PCB of the transmitter, but was almost impossible to move it even with a knive, maybe i move it a little and that helped to improve image quailty too, im not sure... but now image seens more stable and clear,

i decided to mount the camera but when i mount it i see that image is not as clear as when i test it with the full camera dismounted, then i decied to remove the transmitter pcb and glue it in the back of the camera, why? to keep more space between camera and transmitter, and seems image is more clear. Im not sure if that's a subjective feeling but i think image is better when transmitter and camera are not compressed one against the other.

recording quality seems that as been improved too, now i don't see pixelation,

there are still some things i can't reponse, like why ffile size is much more bigger when recording from camera, but any way im much more happy,

i don't recomend to any one to open that cameras, the wires soldered inside are much more sensitive that you think and they broke very easy and are not easy to solder. ( i spend about 1 hour just with that work)

now my problem is how to hold the hot transmitter in the back of the camera... i think i will use thermo-retractable film, but im not sure if it's the best option,

i can't upload a video bcos i removed all the bad quality videos, now i just got a few videos of the test, but i can record one for you if you want,

did you notice that mobibox battery life is much more lower when recording videos?

i usually get more than 3 hours when just playing videos, but when recording just 1 hour (well a little more than that). Seems like if there was not enought power to record, but if you are recording, your player switch off bcos battery is empty, you can switch on the player, and you got enought battery to see maybe 50 min of video... but if you try to record you will get just a few minuts aprox...

sorry my english, i hope u understood all what i said,

that's the cmaera im using, is not a kx131 but i bought it very cheap time ago,

media1556977bi1.jpg

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Well, certainly, MPEG4 -AT-2MBps is going to struggle to encode a noisy picture. Since the PVR has an AGC (Automatic gain control), if the signal levels are low the picture will look noisier, like turning up the volume on a distant radio station.

Sounds like a 'you get what you pay for' scenario with the camera; I've found many of these camera/transmitter combinations that look cheap are really very poor (caveat emptor on eBay!). Spending the extra for something of quality (e.g. the TX40 from RC-Tech) has been definitely worth it in my experience.

The PVR battery life is about right, in my experience; with a 1GB SD card, you can fill it! The on-the-fly encoding is more processor intensive than the decoding, so it uses more power. Note this PVR has the option of recording with the screen switched off, which might help if you're using a bigger SD card.

The circuitry is trying to protect the battery (LiPo) from dropping under 2.5-3v per cell, as this will permanently damage it. Towards the end of their discharge curves most batteries' internal impedance rises. Thus a lower current draw will leave the cell voltage over this critical cut-off (50 mins playback), whereas a higher current draw (recording) will pull the cell voltage below it, and the thing turns itself off (actively) much sooner, to protect the battery.

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thnks for explanation,

you know if there is a way to modify the firmware in order to increase bitrate?

i usually don't record audio so maybe the power reserved to record audio, can be used to record video in a better quality,

i read that firmware can be updated thru SD Card, so maybe something can be done? or that's quite difficult and need lot of work?

Edited by wallaguest1

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