iphone camera iso value - ios

Question

I set the shutter speed, ISO and other camera parameters and capture an image using the code below. If I set the ISO to something like 119, it gets reported as 125 in the Exif info (it is always rounded to a standard value). How can I tell what the real ISO was? The maxISO gets reported as 734 but if I set it to 734 it is 800 in the Exif information. I had the same problem with the exposure time. If I set it to 800ms it shows up as 1s in the but the value calculated from the ShutterSpeedValue is correct.
- (void)setCameraSettings:(long)expTime1000thSec iso:(int)isoValue
{
if ( currentCaptureDevice ) {
[captureSession beginConfiguration];
NSError *error = nil;
if ([currentCaptureDevice lockForConfiguration:&error]) {
if ([currentCaptureDevice isExposureModeSupported:AVCaptureExposureModeLocked]) {
CMTime minTime, maxTime, exposureTime;
if ( isoValue < minISO ) {
isoValue = minISO;
} else if ( isoValue > maxISO ) {
isoValue = maxISO;
}
exposureTime = CMTimeMake(expTime1000thSec, EXP_TIME_UNIT); // in 1/EXP_TIME_UNIT of a second
minTime = currentCaptureDevice.activeFormat.minExposureDuration;
maxTime = currentCaptureDevice.activeFormat.maxExposureDuration;
if ( CMTimeCompare(exposureTime, minTime) < 0 ) {
exposureTime = minTime;
} else if ( CMTimeCompare(exposureTime, maxTime) > 0 ) {
exposureTime = maxTime;
}
NSLog(#"setting exp time to %lld/%d s (want %ld) iso=%d", exposureTime.value, exposureTime.timescale, expTime1000thSec, isoValue);
[currentCaptureDevice setExposureModeCustomWithDuration:exposureTime ISO:isoValue completionHandler:nil];
}
if (currentCaptureDevice.lowLightBoostSupported) {
currentCaptureDevice.automaticallyEnablesLowLightBoostWhenAvailable = NO;
NSLog(#"setting automaticallyEnablesLowLightBoostWhenAvailable = NO");
}
// lock the gains
if ([currentCaptureDevice isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeLocked]) {
currentCaptureDevice.whiteBalanceMode = AVCaptureWhiteBalanceModeLocked;
NSLog(#"setting AVCaptureWhiteBalanceModeLocked");
}
// set the gains
AVCaptureWhiteBalanceGains gains;
gains.redGain = 1.0;
gains.greenGain = 1.0;
gains.blueGain = 1.0;
AVCaptureWhiteBalanceGains normalizedGains = [self normalizedGains:gains];
[currentCaptureDevice setWhiteBalanceModeLockedWithDeviceWhiteBalanceGains:normalizedGains completionHandler:nil];
NSLog(#"setWhiteBalanceModeLockedWithDeviceWhiteBalanceGains g.red=%.2lf g.green=%.2lf g.blue=%.2lf",
normalizedGains.redGain, normalizedGains.greenGain, normalizedGains.blueGain);
[currentCaptureDevice unlockForConfiguration];
}
[captureSession commitConfiguration];
}
}
- (void)captureStillImage
{
NSLog(#"about to request a capture from: %#", [self stillImageOutput]);
if ( videoConnection ) {
waitingForCapture = true;
NSLog(#"requesting a capture from: %#", [self stillImageOutput]);
[[self stillImageOutput] captureStillImageAsynchronouslyFromConnection:videoConnection
completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error) {
if ( imageSampleBuffer ) {
CFDictionaryRef exifAttachments = CMGetAttachment(imageSampleBuffer, kCGImagePropertyExifDictionary, NULL);
if (exifAttachments) {
NSLog(#"attachements: %#", exifAttachments);
} else {
NSLog(#"no attachments");
}
NSLog(#"name: %#", [currentCaptureDevice localizedName]);
NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
UIImage *image = [[UIImage alloc] initWithData:imageData];
[self setStillImage:image];
NSDictionary *dict = (__bridge NSDictionary*)exifAttachments;
NSString *value = [dict objectForKey:#"PixelXDimension"];
[self setImageWidth:[NSNumber numberWithInt:[value intValue]]];
value = [dict objectForKey:#"PixelYDimension"];
[self setImageHeight:[NSNumber numberWithInt:[value intValue]]];
value = [dict objectForKey:#"BrightnessValue"];
[self setImageBrightnessValue:[NSNumber numberWithFloat:[value floatValue]]];
value = [dict objectForKey:#"ShutterSpeedValue"];
double val = [value doubleValue];
val = 1.0 / pow(2.0, val);
[self setImageExposureTime:[NSNumber numberWithDouble:val]];
value = [dict objectForKey:#"ApertureValue"];
[self setImageApertureValue:[NSNumber numberWithFloat:[value floatValue]]];
NSArray *values = [dict objectForKey:#"ISOSpeedRatings"];
[self setImageISOSpeedRatings:[NSNumber numberWithInt:[ [values objectAtIndex:0] intValue]]];
NSLog(#"r/g/b gains = %.2lf/%.2lf/%.2lf",
currentCaptureDevice.deviceWhiteBalanceGains.redGain,
currentCaptureDevice.deviceWhiteBalanceGains.greenGain,
currentCaptureDevice.deviceWhiteBalanceGains.blueGain);
[[NSNotificationCenter defaultCenter] postNotificationName:kImageCapturedSuccessfully object:nil];
} else {
NSLog(#"imageSampleBuffer = NULL");
}
waitingForCapture = false;
}];
} else {
NSLog(#"can't capture from: videoConnection");
}
}

Answer 1

I answered your other question, same thing, you are not setting the CustomSettings mode:
[device lockForConfiguration:nil];
if([device isExposureModeSupported:AVCaptureExposureModeCustom]){
[device setExposureMode:AVCaptureExposureModeCustom];
[device setExposureModeCustomWithDuration:exposureTime ISO:exposureISO completionHandler:^(CMTime syncTime) {}];
[device setExposureTargetBias:exposureBIAS completionHandler:^(CMTime syncTime) {}];
}
Regards.

Answer 2

I added:
[device setExposureMode:AVCaptureExposureModeCustom];
and changed my completionHandler from nil to:
completionHandler:^(CMTime syncTime) {}
and I still see the same results. It seems that ISO can only be set to the "standard" values and not to any value between minISO and maxISO.