Flintstone
Well-known member
I'm a bit at a loss when I hear the term latitude. What is it exactly that is being to expressed, technically speaking?
What is latitude?
- Thread starter Flintstone
- Start date
Re: What is latitude?
its nearly interchangeable with "dynamic range" sometimes and is short for "exposure lattitude"
..basically "exposure latitude" is the range of exposure that the sensor can handle..
..and "dynamic range" desribes the resulting range of tones between black and white in the image.
the more exposure latitude the sensor has.. the more the dynamic range in its imagery. in other words if the CCD has a large amount of exposure latitude it can handle a greature exposure range and the image it produces will have an increased dynamic range from its brightest point(white) to its darkest point (black) because what might be blown out with less exposure latitude could be picked up within the exposure range in a wider latitude and show detail in the highlights. and what might be black with less latitude would be picked up within the range as well and show detail in the shadows. so the image overall would have an increased number of tones from white to black or a wider "dynamic range".
its nearly interchangeable with "dynamic range" sometimes and is short for "exposure lattitude"
..basically "exposure latitude" is the range of exposure that the sensor can handle..
..and "dynamic range" desribes the resulting range of tones between black and white in the image.
the more exposure latitude the sensor has.. the more the dynamic range in its imagery. in other words if the CCD has a large amount of exposure latitude it can handle a greature exposure range and the image it produces will have an increased dynamic range from its brightest point(white) to its darkest point (black) because what might be blown out with less exposure latitude could be picked up within the exposure range in a wider latitude and show detail in the highlights. and what might be black with less latitude would be picked up within the range as well and show detail in the shadows. so the image overall would have an increased number of tones from white to black or a wider "dynamic range".
Flintstone
Well-known member
Re: What is latitude?
So basically, greater latitude is achieved by a combination of, color depth (8-bit vs. 10-bit), DSP processing in bit-witdth (10, 12, or 14 bit), and probably color sambling (4:1:1 vs 4:2:2)? I suppose that the CCD sensors probably have physical limits in their rendering of the imagery, but would the CCD size and pixel density affect latitude, as well as the optics? I would assume that the DV codec also cuts down in the dynamic range because of it's high compression. When all considered, I'm surprised that there isn't as much color banding issues (except maybe in post when certain effects are applied). Am I missing anything else?
So basically, greater latitude is achieved by a combination of, color depth (8-bit vs. 10-bit), DSP processing in bit-witdth (10, 12, or 14 bit), and probably color sambling (4:1:1 vs 4:2:2)? I suppose that the CCD sensors probably have physical limits in their rendering of the imagery, but would the CCD size and pixel density affect latitude, as well as the optics? I would assume that the DV codec also cuts down in the dynamic range because of it's high compression. When all considered, I'm surprised that there isn't as much color banding issues (except maybe in post when certain effects are applied). Am I missing anything else?
Barry_Green
Moderator
Re: What is latitude?
CCD size (or, more appropriately, pixel size on the CCD) definitely affects it as well. Tinier pixels have less capacity to gather and hold a charge, larger pixels can store a wider charge, so the larger your pixels are, the more dynamic range they can resolve (all other things being equal).
CCD size (or, more appropriately, pixel size on the CCD) definitely affects it as well. Tinier pixels have less capacity to gather and hold a charge, larger pixels can store a wider charge, so the larger your pixels are, the more dynamic range they can resolve (all other things being equal).
Re: What is latitude?
Barry, are you sure it's that simple? 1/2.5'' digicams have better dynamic range than the dvx (though not by much) despite much smaller photosites. Also, 35mm film has way better dynamic range than does 16mm (though, oddly, I didn't notice that 70mm was that much better than 35, though the resolution was mind-boggling). What accounts for that if not something as simple as the sensor size?
Barry, are you sure it's that simple? 1/2.5'' digicams have better dynamic range than the dvx (though not by much) despite much smaller photosites. Also, 35mm film has way better dynamic range than does 16mm (though, oddly, I didn't notice that 70mm was that much better than 35, though the resolution was mind-boggling). What accounts for that if not something as simple as the sensor size?
Barry_Green
Moderator
Re: What is latitude?
Digicams use different technology from video sensors. You have to compare apples to apples. And a larger digicam sensor, of equal pixel density (meaning larger pixels) will deliver better latitude and sensitivity than the smaller sensor. But you can't directly compare video chips with still-camera chips.
As for film, it's exactly the same thing -- the larger the sensor, the larger the surface the light gets spread across, and the more sensitivity/latitude you get from it. Bigger sensors = better, but only as long as all other things stay equal; a 4x bigger sensor with 4x the pixel count will be higher resolution, but no better at dynamic range or sensitivity than the smaller sensor. A 4x bigger sensor with the same pixel count as the smaller sensor will have 4x bigger pixels, so for the same resolution you'll get much better latitude and sensitivity.
Digicams use different technology from video sensors. You have to compare apples to apples. And a larger digicam sensor, of equal pixel density (meaning larger pixels) will deliver better latitude and sensitivity than the smaller sensor. But you can't directly compare video chips with still-camera chips.
As for film, it's exactly the same thing -- the larger the sensor, the larger the surface the light gets spread across, and the more sensitivity/latitude you get from it. Bigger sensors = better, but only as long as all other things stay equal; a 4x bigger sensor with 4x the pixel count will be higher resolution, but no better at dynamic range or sensitivity than the smaller sensor. A 4x bigger sensor with the same pixel count as the smaller sensor will have 4x bigger pixels, so for the same resolution you'll get much better latitude and sensitivity.
J_Barnes
Veteran
Re: What is latitude?
Just to add another take:
I learned about latitude in shooting film, where more often it is described in T/F-stop ranges rather then by comparing sensiometric exposure curves.
After shooting a film test, I would know that a particular film is able to resolve detail to a specific stop range above and below my nominal exposure rating. For example, three stops below and two stops above indicate a latitude of 6 stops. Knowing that, I can meter a scene and know exactly what individual tones are going to fall into detail and what is going to be lost in the toe or blown out at the shoulder. Once I understood latitude in terms of actual T-Stop ranges, I found it much easier to be confident in the application of light within a given scene.
THe only reason why I post this is because electronic "dynamic range" is very conceptual, and it doesn't really give me any help in lighting a scene unless I know exactly where my correct exposure, highlight and shadow tones are falling in a scene and on the curve. Correct exposure is probably never at the mid-point of dynamic range, and in video you tend to have even less shoulder latitude then you do in film, so I personally need an incremental measurement to go by.
Working with stops as a signpost, you might get a better idea of how far up and down the dymanic range you can deviate from your correct exposure and still retain detail.
Just to add another take:
I learned about latitude in shooting film, where more often it is described in T/F-stop ranges rather then by comparing sensiometric exposure curves.
After shooting a film test, I would know that a particular film is able to resolve detail to a specific stop range above and below my nominal exposure rating. For example, three stops below and two stops above indicate a latitude of 6 stops. Knowing that, I can meter a scene and know exactly what individual tones are going to fall into detail and what is going to be lost in the toe or blown out at the shoulder. Once I understood latitude in terms of actual T-Stop ranges, I found it much easier to be confident in the application of light within a given scene.
THe only reason why I post this is because electronic "dynamic range" is very conceptual, and it doesn't really give me any help in lighting a scene unless I know exactly where my correct exposure, highlight and shadow tones are falling in a scene and on the curve. Correct exposure is probably never at the mid-point of dynamic range, and in video you tend to have even less shoulder latitude then you do in film, so I personally need an incremental measurement to go by.
Working with stops as a signpost, you might get a better idea of how far up and down the dymanic range you can deviate from your correct exposure and still retain detail.
Re: What is latitude?
I suppose shooting with master ped at 0, underexposing slightly, and using the zebra lines carefully is the best approach to keeping as much detail as possible, but I agree....most of my footage ends up over-exposed or under-exposed and my footage that comes out right often has unavoidable blown highlights. I think video's limited dynamic range is something you just have to deal with, especially with prosumer NTSC equiptment.
I suppose shooting with master ped at 0, underexposing slightly, and using the zebra lines carefully is the best approach to keeping as much detail as possible, but I agree....most of my footage ends up over-exposed or under-exposed and my footage that comes out right often has unavoidable blown highlights. I think video's limited dynamic range is something you just have to deal with, especially with prosumer NTSC equiptment.
