On 05/27/2016 02:52 PM, Nick Dyer wrote: > On 27/05/2016 13:38, Hans Verkuil wrote: >> On 05/04/2016 07:07 PM, Nick Dyer wrote: >>> + <refname><constant>V4L2_PIX_FMT_YS16</constant></refname> >>> + <refpurpose>Grey-scale image</refpurpose> >>> + </refnamediv> >>> + <refsect1> >>> + <title>Description</title> >>> + >>> + <para>This is a signed grey-scale image with a depth of 16 bits per >>> +pixel. The most significant byte is stored at higher memory addresses >>> +(little-endian).</para> >> >> I'm not sure this should be described in terms of grey-scale, since negative >> values make no sense for that. How are these values supposed to be interpreted >> if you want to display them? -32768 == black and 32767 is white? > > We have written a utility to display this data and it is able to display > the values mapped to grayscale or color: > https://github.com/ndyer/heatmap/blob/master/src/display.c#L44 > > An example of the output is here: > https://www.youtube.com/watch?v=Uj4T6fUCySw > > The data is intrinsically signed because that's how the low level touch > controller treats it. I'm happy to change it to "Signed image" if you think > that would be better. A V4L2_PIX_FMT_ definition must specify the format unambiguously. So it is not enough to just say that the data is a signed 16 bit value, you need to document exactly how it should be interpreted. Looking at the code it seems that the signed values are within a certain range and are normalized to 0-max by this line: ssize_t gray = (data[i] - cfg->min) * max / (cfg->max - cfg->min); Are the min/max values defined by the hardware? Because in that case this pixel format has to be a hardware-specific define (e.g. V4L2_PIX_FMT_FOO_S16). Only if the min/max values are -32768 and 32767 can you really use YS16 (not sure yet about that name, but that's another issue). Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
