More re Crops

More tests - Very interesting.

I have come to the conclusion that when the crop modes are activated all other pixels (Photo sites) outside the crop are turned Off ie they don't register on the sensor, here's why;

If you look at 1.7 the exposure is duller but more accurate to a 18% grey card and White Balance is correct.

In the 1.3 crop the exposure is lighter and WB is starting to tend toward Magenta both trying to compensate for the darker blue background of the desk.

With no crop their is much more blue desk in the Original Photo (before equalizing the crop) and we see the lightest exposure and most magenta.

I have to also expect that crop modes will decrease writes speeds and hence increase buffers in Hi Speed Shutters - more testing to come.

CONCLUSION; It is definitely worth cropping in Camera rather than Post - You are eliminating a lot of unwanted Light.

Original Shots

ozdean wrote:

More tests - Very interesting.

I have come to the conclusion that when the crop modes are activated all other pixels (Photo sites) outside the crop are turned Off ie they don't register on the sensor, here's why;

If you look at 1.7 the exposure is duller but more accurate to a 18% grey card and White Balance is correct.

In the 1.3 crop the exposure is lighter and WB is starting to tend toward Magenta both trying to compensate for the darker blue background of the desk.

With no crop their is much more blue desk in the Original Photo (before equalizing the crop) and we see the lightest exposure and most magenta.

I have to also expect that crop modes will decrease writes speeds and hence increase buffers in Hi Speed Shutters - more testing to come.

CONCLUSION; It is definitely worth cropping in Camera rather than Post - You are eliminating a lot of unwanted Light.

Original Shots

Interesting. About the buffer, no, it makes no difference. Full image, or either crop will fire off the same burst amount. They don't seem to process any faster either.

I wonder why the buffer and write speed don't Change? The file is smaller.

ozdean wrote:

I wonder why the buffer and write speed don't Change? The file is smaller.

Just a WAG, but maybe because it's a completely different bottleneck elsewhere in the system? Or maybe pixel mapping forces ones or zeros into those unused areas in order to meet some kind of CRC while it offloads the sensor and it strips them later as the file is written? I dunno, but you are right, it is odd that the designers would leave money on the table so to speak, if it was doable, you'd think they would have done it and bragged on it too.

Yes Eric I know nothing about programming but I'm sure the outside areas are turned off after this test - you'd think there would be a capacity advantage?

Hi KPM 2

That is a good idea to use a small light and just check the metering , this would confirm if the metering is confined to the crop area.

I have just done it and the metering really drops off in the outer area but still works. I guess it is still getting glow from the light in the cropped area.

If this series was taken with Automatic White Balance ON,  I'd have to wonder if the color of the table the manual rests on is contributing to differences.

Theoretically, the manual should be on an 18% gray table.

When I worked in a commercial photo lab, none of our printers could render accurate color balance if an object that required correct color balance was on a colored background.  We had 5 different types of color printers, and all failed that.

Might this explain color shift here ??

Yes it is and that proves that the area outside the OVF crop frame is discarded in determining WB & EXP - Camera was kept at the same height above the desk.

That's odd I thought the Crop function was sold on the faster fps and buffer increased?

Yes John - It would be good if it could but doesn't seem to.

That's so strange but in this crazy world 🌎  nothing is certain, apart from Pentax ergonomics which are yet to be surpassed. Keep up the good work Dean, you get some beautiful BIF always an ambassador for the Pentax brand 😀 👍

ozdean wrote:

I wonder why the buffer and write speed don't Change? The file is smaller.

Not having the camera I'm guessing.

You had a theory that what is read from the sensor in crop mode is different,

I believe this for the K1 because in crop mode the FPS goes up. This suggests to me that the time to reset the sensor for the next frame reduces. The mechanical parts will go at 7 fps but the read out from the chip will only go support 4 fps in full frame mode, but the will go faster in crop mode. Since the chip can be told to give a video res frame at more frequent intervals, there must be ways of asking it for different things.

I've also wondered about where in the pipeline the buffer is.
There is a pipeline of sensor (A-D converter) , Prime chip, memory card. There's no real lower limit for the speed of the memory card, so it has always seemed the sensible thing to have the buffer after the prime chip, and what we see in the specs backs this up. It looks like frames arrive in the buffer as fast as they are shot, so the prime can process something like 160MPixels / sec.

However I've wondered if there is a way of doing it the other way around. Slow the prime chip down (and generate less heat and use less power) to match the write speed of the memory card, and buffer the unprocessed frames, although frames in buffer doesn't change with different file options, the number of frames to stall the buffer does. (if the buffer is 10 frames, and you can write 1 in the time it takes to shoot 10 you stall at 11, but if you can write 5 in the time it takes to shoot 10,  you have 5 still in the buffer after 10, and you'll have shot 20 by the time the buffer is full).

If the crop happens in processing AND an "early" buffer is imposing a limit, that would explain it. It might be more simply explained by something in the firmware not raising a limit when the mode changes.

Thanks John.

Thanks James I appreciate your knowledge re the technical side of this.

To my simple (Mechanical) mind it seems the crop is done on the sensor and there should be less info to pass through the system.

I realize the frame rate can't change as that is mechanical but it would be nice if write speed could be enhanced?