The ADV7625/ADV7626/ADV7627 offer a simple low cost on screen display for video overlay on HDMI. The hardware implementation uses Text boxes ( Tbox), filled boxes ( Fbox) and icon boxes (Ibox) to create basic text based OSD overlay. The hardware offers a 16×16 resolution for text characters with ability to scale from 1 to 15 using pixel repetition. The pixel repetition in most cases does not provide good quality text as a result. The Blimp OSD Designer software tool abstracts the drawing hardware components and optimizes their use by treating them all as graphic components that can display both images or text and can span across multiple 16×16 boundaries in the case of Tboxes to create larger high quality fonts. On larger resolutions like 1080p and 4k, a compromise will usually have to be made between limiting OSD content or using scaling to have more content but with lower resolution.
This application note details the capabilities of the ADV7625 OSD as implemented in Blimp. with these guidelines, user can plan the graphic and text layout of each pages for their OSD design. the best way to verify is by using Blimp to add graphics and text to a page and test it with the OSD hardware emulator which comes with Blimp.
ADV7625 - 3GHz HDMI 5:2 cross point Transceiver with On-Screen Display
ADV7626 - 3GHz HDMI 2:2 cross point Transceiver with On-Screen Display
Table 1: Tbox image size limits by number of colors ( with scaling = 1 )
# colors | Pixels span Tbox limit ( if some glyphs are identical)) | Pixel span Glyph limit ( can be more if some 16×16 blocks are re-used) |
---|---|---|
1 | 262144 ( 64 blocks of 256 x 16) | 65536 |
2 | 131072 ( 32 blocks of 256 x 16) | 32768 |
3 | 86016 ( 21 blocks of 256 x 16) | 21760 |
4 | 65536 ( 16 blocks of 256 x 16) | 16384 |
5 | 49152 ( 12 blocks of 256 x 16) | 13056 |
6 | 40960 ( 10 blocks of 256 x 16) | 10752 |
7 | 36864 ( 9 blocks of 256 x 16) | 9216 |
8 | 32768 ( 8 blocks of 256 x 16) | 8192 |
9 | 28672 ( 7 blocks of 256 x 16) | 7168 |
10 | 28672 ( 6 blocks of 256 x 16) | 6400 |
11 | 20480 ( 5 blocks of 256 x 16) | 5888 |
12 | 20480 ( 5 blocks of 256 x 16) | 5376 |
13 | 16384 ( 4 blocks of 256 x 16) | 4864 |
14 | 16384 ( 4 blocks of 256 x 16) | 4608 |
15 | 16384 ( 4 blocks of 256 x 16) | 4352 |
16 | 16384 ( 4 blocks of 256 x 16) | 4096 ( same as Ibox) |