Avid Resolutions Compared

Working on an Avid Media Composer Adrenaline at online resolutions most of the time, I have been curious about the various resolutions and compressions available to me. I have not been able to find any satisfactory comparisons focusing on the visual quality of the compression techniques.

So, I have conducted some research of my own, I think it provides a reasonable overview of the quality of the resolutions. This was all done with PAL footage, but I assume that roughly the same results will be had with NTSC.

Technique

I captured a small clip from a Digital Betacam tape at all the resolutions I wished to test, and then exported a representative still from Avid using an uncompressed TGA export setting.

Opening each file in Photoshop, I created a single file that contained each still on a layer on it’s own, and applied the ‘Difference‘ blending mode. Each layer was differenced against the 1:1 reference capture to issolate places where the recorded image varied. I then applied a adjustment layer than cropped the levels to between 0 and 32 (or 1/8 of the image’s total range) to highlight the variances.

To get some sort of accurate and consistant measure of the level of variance, I used Photoshop’s histogram tool to give me statistics on the resulting difference image (without the levels applied) - this gives us two useful measures, Standard Deviation telling us how far the lumanance levels in the diff vary, and the Mean, which demonstrates the average lumananance in the picture. As I figure it, the lower the number, the less the picture has varied from the 1:1 reference image.

	Frame Segment
2:1	3:1	10:1
MPEG50	MPEG40	MPEG30
	DV25 4:2:0

Results

(These Meridian bitrates are estimates)

Based on these results, I’d rate these compressions in the following order:

Notes

Obviously DV25 suffers in this case due to it’s 4:2:0 sampling method, although it does general produce what I think is a better picture than 10:1 in most cases. MPEG IMX is a 4:2:2 I-frame MPEG2 codec. I am not clear what sampling method is employed by the Meridian codec.

The footage I have used in this case represents what I feel is a reasonable representation of an average frame of video. It has a wide dynamic range, a good range of colours, skin tones and moderately complex fine detail in some areas of the picture. I suspect other images will yeild different results - complex tree patterns are a prime example.

The sample footage was shot on a Sony DVW-790P, onto Sony stock, played in a DVW500AP, captured via SDI into an Avid Media Composer Adrenaline.