|The video delay in the iScan Ultra should be either the same or one frame less. We capture the SiI504 output and then display it so we can have a programmable output frame rate. I don't know if the FPGA in the iScan Ultra does this or not.
The scaler FPGA in the iScan Ultra does not add an extra full frame of delay. It only delays the output video signal by the number of lines needed for aspect ratio conversion of letterbox 4:3 sources to 16:9 (which is on the order or 60 lines or so). It always adds this delay so that there are no disturbances in the output timing when the input aspect ratio is changed. Note that the video processing delay through the SiI504 is not always 67 ms and can vary between 3 field periods and 4 field periods. For processing of true interlaced video signals the delay is 3 field periods; for processing of progressive sources (3:2 and 2:2 PD) the delay can be 4 field periods.
|Differences between the Vision and iScan Ultra
- We cost about $300 less (MSRP).
- We have a very good scaler.
- We have more features.
- We use a better TV decoder (IMO).
- We oversample our output so even at 480p we look better (IMO).
- As reported by Allan Jayne, we have a very good chroma filter. I can't
say exactly how good the iScan Ultra is for this.
- The Ultra does have more inputs than the Vision (but less than the
VisionPro), and a DVI output. If you can live with 480p these might
be useful to you.
Here's a slightly different point of view on some of the points you make above (and a few others):
- I can find the iScan Ultra from a number of sources with a street price somewhat less than the Vision's MSRP. Are there any sources for the Vision that sell at less than MSRP?
- The Ultra only provides the modest amount of scaling needed to do aspect ratio conversion, so the Vision's scaler is unquestionably more capable.,
- The Vision has different features than the Ultra; it might be debatable whether or not there are 'more', but the Vision certainly appears to have a lot more adjustability than the Ultra. The Vision has a very configurable output section (scaler, frame rate conversion, test pattern generation, etc.), while the Ultra has more inputs, DVI output, switchable chroma filter, and separate controls for boosting/cutting fine detail and strong edges.
- The video decoder in the Ultra also oversamples at 2X (as you mentioned the Vision's does in a previous post), although it uses 9-bit ADCs while the Vision has 10-bit ADCs.
- The Ultra's output is also oversampled - 4X (108 MHz) for luma and 8X (also 108 MHz) for chroma. Also, the Ultra has 12-bit DACs while the Vision has 10-bit DACs.
- Can the Vision's chroma filter be turned off? If not, then it reduces vertical chroma resolution on sources without a CUE or ISP problem.
- The bandwidth of the Vision's passthrough input (300 MHz, I think) is much higher than the Ultra's. The Ultra is primarily a 480p device and the passthrough has a bandwidth of about 35 MHz, which is more than adequate for 480p (and arguably OK for 1080i or 720p).
- The output of the iScan Ultra is frame-locked to the input field rate (which can be both good and bad). Does the Vision offer this capability?
That being said, the Ultra is certainly limited in that it is only a deinterlacer, while the Vision is a scaler. If 480p is all you need then the Ultra may be fine; if you need higher resolution than 480p then the Vision will provide this while the Ultra can't.
One other observation here: the DVI output of the Ultra allows a digital data connection to a display device. If you have a display with a DVI input and a good internal scaler, then the Vision may not offer an advantage since the end quality could well be the same (assuming the display's scaler and the Vision's scaler are comparably in quality/performance). There may even be a performance advantage for the Ultra when used with fixed-pixel displays since there will be an extra set of conversions (digital-to-analog-to-digital) performed with the Vision since it doesn't have a digital output and the display would have to digitize the Vision's analog output.
Jim, I also have a few related questions about the Vision (Pro):
1) If frame rate conversion is set to 72 (48) Hz, does the Vision produce exactly 3 (2) output frames for each film frame of a 24 fps source? I.e., at 72 (48) Hz output is the Vision's output frame rate locked to the original source input frame rate?
2) The frame rate conversion of the Vision looks to be very flexible. Is there any mode where the output frame rate is locked 1:1 with the input field rate? If not, then the Vision must sometimes add/subtract a frame, causing jumps or stutters in smooth motion even though the output frame rate is programmed to be the 'same' as the input field rate. On the other hand, this will totally decouple the output timing from the input timing so you effectively have a full-frame TBC.
3) Is the chroma filtering you reference above always on? Is this implemented as part of the integral lowpass filtering performed in the vertical scaler, or is there a separate (hopefully, switchable) filter section for vertical chroma filtering?
4) Does the frame rate conversion in the Vision add only a single extra frame period delay, or does the delay vary depending on the frame-phase relationship between the input and output?
5) Is the frame rate conversion process double buffered, or can there be tearing in the output?
I also have a question for Allan:
If you display the 200 TVL resolution pattern from the AVIA disc, so you see:
- Noise in the image, displayed as a flickering in the black and white high resolution line patterns?
- Scaling artifacts (e.g., varying intensity) in the black and white line patterns?
- Moire-type patterns in the vertical resolution wedge (similar to what you see on the horizontal wedge when the signal is not scaled)?
- Dale Adams