Data Views of Shooting Habits

I try to ensure there is as much metadata available as possible for the main images on my website; to see it, click the (info) icon in the 'lightbox' view (available when viewing a gallery of images, e.g. Gants Hill in Project 269).

Obviously the exposure control settings (aperture, shutter speed and ISO sensitivity) are important to understand how an image was made; but, I decided, so are the optical properties (subject distance, focal length and depth-of-field).

In theory all this information is available in the image EXIF data, but over the years with various changes in workflows, the fulfillment is patchy. I've done sme cleaning up so that most 'gallery' images have good data (incidental images within articles generally don't).

However I found that only about a third of my images were managing to report subject (or approximate focus) distance. It turned out that by digging deeper (into the XMP metadata, not justt he EXIF) I was able to extract subject distance for around two thirds of my images. So I did a bunch of extra coding to extract subject distance.

While I was about it I thought "why not export all the metadata for all images as CSV?" - so I did that.

This allowed me to create two charts representing the history of my shooting behaviour:

Exposure Control: aperture, shutter speed and ISO settings used for around 1,200 images
Image Control: subject distance, focal length and depth-of-field for around 750 images

In both cases the images spanned around 15 years of shooting and so give a broad view of my shooting habits; presenting a part of my personal 'visual signature'

Chart 1: Exposure Control

Bubble chart showing ISO for aperture and shutter speed of 1,200 images

It's clear I favour f/8, shooting mostly between f/4 and f/11.

It's also clear that I have a strong affinity with ISO:400, which drives my average shutter speed quite low. This reflects a lot of my recent work being shot on a tripod in the studio. I can see the ISO does rise around the slower shutter speeds - and I expect that was from shooting in dimly lit performance venues.

Chart 2: Image Control

Bubble chart showing depth-of-field for subject distance and focal length of 750 images

It's clear that I'm mostly working with pretty limited depth-of-field, in fact I'm suprised by how little varition there is. I think this comes from the fact that most of my photography is about 'details' (reasons for seeing) than about 'vistas' or 'scenes'.

In Summary

I think these charts are a joy, beautiful to look at, and I really only made them because I could. However, they do give me a new (if somewhat minor) way of looking at my approach to my work - and I think anything that does that, is to be welcomed.

In case it is useful, here's the PHP script I wrote to extract metadata from a JPG:

Metadata Extraction

PHP Script

function metaEval ($s,$precision=0) {
    $eparts = explode('/',$s);
    if (count($eparts)<2) return $s;
    if (!is_numeric($eparts[0])) return $s;
    if (!is_numeric($eparts[1])) return $s;
    $numerator = intval($eparts[0]);
    $denominator = intval($eparts[1]);
    if ($denominator===0) return $s;
    $v = (float) $numerator / (float) $denominator;
    return round($v,$precision);
} // metaEval

function metaNormalise ($s) {
    $eparts = explode('/',$s);
    if (count($eparts)<2) return $s;
    if (!is_numeric($eparts[0])) return $s;
    if (!is_numeric($eparts[1])) return $s;
    $numerator = intval($eparts[0]);
    if ($numerator===1) return $s;
    $denominator = intval($eparts[1]);
    if ($denominator===0) return $s;
    $v = (float) $denominator / (float) $numerator;
    return '1/'.intval(round($v));
} // metaNormalise

class rawTag {
    public function resolve ($exif) {
        if (!is_array($exif)) return '';
        if (!array_key_exists($this->section,$exif)) return '';
        if (!array_key_exists($this->name,$exif[$this->section])) return '';
        $value = $exif[$this->section][$this->name];
        if ($this->evaluate!==false) $value = metaEval($value,$this->evaluate);
        if ($this->normalise) $value = metaNormalise($value);
        return $value;
    } // resolve

    private $section = '';
    private $name = '';
    private $evaluate = false;
    private $normalise = false;
    
    function __construct($s,$name,$e,$n) {
        $this->section = $s;
        $this->name = $name;
        $this->evaluate = $e;
        $this->normalise = $n;
    } // __construct
} // rawTag

class derivedTag {
    public $rawTags = array ();
    public $asData = '';
    
    public function resolve($exif) {
        if ($this->numericData) {
            $this->asData = 0;
        }
        else {
            $this->asData = '""';
        }
        if (count($this->rawTags)<1) return '';
        foreach ($this->rawTags as $rawTag) {
            $value = $rawTag->resolve($exif);
            if ($value==='') continue;
            if ($this->exclusions) {
                if (str_starts_with($value,'4294967295')) continue;
                if (str_starts_with($value,'4294967296')) continue;
                if (str_starts_with($value,'2147483647')) continue;
            }

            $data = $value;
            if ($this->prefix!=='')
                if (str_starts_with($data,$this->prefix)) 
                    $data = substr($data,strlen($this->prefix));
            if ($this->suffix!=='')
                if (str_ends_with($value,$this->suffix)) 
                    $data = substr($data,0,strlen($data)-strlen($this->suffix));
            if ($this->numericData) {
                $data = metaEval($data,10);
            }
            else {
                $data = '"'.$data.'"';
            }
            $this->asData = $data;
            
            if ($this->thousands) $value = number_format($value);
            if ($this->prefix!=='')
                if (!str_starts_with($value,$this->prefix)) 
                    $value = $this->prefix.$value;
            if ($this->suffix!=='')
                if (!str_ends_with($value,$this->suffix)) 
                    $value = $value.$this->suffix;
            return $value;
        }
        return '';
    } // resolve
    
    private $numericData = false;
    private $prefix = '';
    private $suffix = '';
    private $exclusions = false;
    private $thousands = false;
    
    function __construct ($n,$p,$s,$e,$t) {
        $this->numericData = $n;
        $this->prefix = $p;
        $this->suffix = $s;
        $this->exclusions = $e;
        $this->thousands = $t;
    } // __construct
} // derivedTag

// Can't extract height and width as it is either Sensor Dimensions,
// without regard for crop OR it is the resized-for-web Dimensions
// none of the values tell me the original processed image dimensions...

function resolveMeta ($filename,$tags) {
    $resolved = array ();

    $ext = pathinfo($filename,PATHINFO_EXTENSION);
    if  ($ext!=='jpg') return $resolved;
    
    $exif = exif_read_data($filename,null,true,false);
    if ($exif===false) return $resolved;
    
    $resolved['Name'] = pathinfo($filename,PATHINFO_FILENAME);
    
    $resolved['csv'] = $resolved['Name'];
    foreach ($tags as $key => $tag) {
        $v = $tag->resolve($exif);
        $resolved['csv'] .= ','.$tag->asData;
        if ($v!=='') $resolved[$key] = $v;
    }
    
    if (!array_key_exists('Distance',$resolved)) {
        try {
            $value = '';
            $find = 'aux:ApproximateFocusDistance';
            $fLen = strlen ($find);
            $content = file_get_contents($filename);

            $pos = strpos($content,$find);
            if ($pos!==false) {
                $distance_start = $pos+$fLen+1;
                $xmp_data = substr($content, $distance_start);

                if (str_starts_with($xmp_data,'"')) {
                    $vparts = explode('"',$xmp_data,3);
                    if (count($vparts)>1) $value = $vparts[1];
                }
                else {
                    $vparts = explode('<',$xmp_data,3);
                    $value = $vparts[0];
                }

                if (($value!=='') && 
                    !str_starts_with($value,'4294967295') &&
                    !str_starts_with($value,'4294967296') &&
                    !str_starts_with($value,'2147483647')) {

                    $value = sprintf('%0.2f',metaEval($value,2)).'m';
                    $resolved['Distance'] = $value;
                }
            }
        }
        catch (Exception $e) {
        }
    }
    
    $resolved['html'] = '<div>';
    if (count($resolved)>2) {
        if (array_key_exists('Model',$resolved)) {
            $resolved['html'] .= '<p>'.$resolved['Model'].'</p>';
        }
        
        $e = '';
        if (array_key_exists('ShutterSpeed',$resolved)) 
            $e .= $resolved['ShutterSpeed'].' ';
        if (array_key_exists('Aperture',$resolved)) 
            $e .= $resolved['Aperture'].' ';
        if (array_key_exists('ISO',$resolved)) 
            $e .= $resolved['ISO'];
        $e = preg_replace('/\s+/', ' ', $e);
        $e = trim($e);
        if ($e!=='') 
            $resolved['html'] .= '<p>'.$e.'</p>';
        
        $l = '';
        if (array_key_exists('FocalLength',$resolved)) 
            $l .= $resolved['FocalLength'].' ';
        if (array_key_exists('Distance',$resolved)) 
            $l .= '@'.$resolved['Distance'].' ';
        if (array_key_exists('Lens',$resolved)) 
            $l .= ' ('.$resolved['Lens'].')';
        $l = preg_replace('/\s+/', ' ', $l);
        $l = trim($l);
        if ($l!=='') 
            $resolved['html'] .= '<p>'.$l.'</p>';

        if (array_key_exists('Date',$resolved)) {
            $resolved['html'] .= '<p>'.$resolved['Date'].'</p>';
        }
    }
    else {
        $resolved['html'] .= '<p>No Metadata</p>';
    }
    $resolved['html'] .= '</div>';

    return $resolved;
    
} // resolveMeta

function getMeta ($filename) {
    $tags = [];
    
    $tags['Aperture']     = new derivedTag(true, 'f/',  '',  false,false);
    $tags['Distance']     = new derivedTag(true, '',    'm', true, false);
    $tags['Model']        = new derivedTag(false,'',    '',  false,false);
    $tags['Date']         = new derivedTag(false,'',    '',  false,false);
    $tags['Lens']         = new derivedTag(false,'',    '',  false,false);
    $tags['ShutterSpeed'] = new derivedTag(true, '',    's', false,false);
    $tags['ISO']          = new derivedTag(true, 'ISO:','',  false,true);
    $tags['FocalLength']  = new derivedTag(true, '',    'mm',false,false);
    
    $tags['Aperture']->rawTags[] = 
        new rawTag('COMPUTED','ApertureFNumber',false,false);
    $tags['Aperture']->rawTags[] = 
        new rawTag('EXIF','FNumber',            false,false);

    $tags['Distance']->rawTags[] = 
        new rawTag('COMPUTED','FocusDistance',  false,false);
    $tags['Distance']->rawTags[] = 
        new rawTag('EXIF','SubjectDistance',    2,    false);
        
    $tags['Model']->rawTags[] = 
        new rawTag('IFD0','Model',              false,false);

    $tags['Date']->rawTags[] = 
        new rawTag('EXIF','DateTimeOriginal',   false,false);
    $tags['Date']->rawTags[] = 
        new rawTag('IFD0','DateTime',           false,false);

    $tags['Lens']->rawTags[] = 
        new rawTag('EXIF','UndefinedTag:0xA434',false,false);
    $tags['Lens']->rawTags[] = 
        new rawTag('IFD0','UndefinedTag:0xA434',false,false);

    $tags['ShutterSpeed']->rawTags[] = 
        new rawTag('EXIF','ExposureTime',       false, true);

    $tags['ISO']->rawTags[] = 
        new rawTag('EXIF','ISOSpeedRatings',    false,false);

    $tags['FocalLength']->rawTags[] = 
        new rawTag('EXIF','FocalLength',        0,    false);
    
    return resolveMeta($filename,$tags)['html'];

} // getMeta

Data Views of Shooting Habits | Photography | Ant Smith

Chart 1: Exposure Control

Chart 2: Image Control

In Summary

Metadata Extraction

PHP Script