Saturday 29 January 2011

Digital Photographic Practice Exercise 11 Raw




The top image of the pair is the Raw image and the lower the jpg image. Both are necessarily shown as jpg files. These images are used for the high dynamic range of the image.

The raw converter I use allows for both raw and jpg files to be 'converted'. The only differences are that with the raw file there is both camera calibration and lens correction available. They were both applied to the top image.

White balance was set using the white balance tool and the same area of the image used.

Exposure - As a first try 'Auto' exposure was tried but in both cases it produced an image that was too light and lacking in contrast. Adjustments were made using the sliders with readings: (the first figure was applied to the raw image the second to the jpg image)

Exposure -0.7/-1.35;  Recovery 53/30; Fill light 6/16; Brightness 36/36; Contrast Strong/Strong; Clarity 64/64; Vibrance 32/32.

Local adjustment use the Adjustment tool was applied to the bright face of the rotunda to darken it.

Both images were were reduced in size, mode was changed from 16 bits to 8 bits and sharpened using the same settings.

Examination of the images at 100% prior to reduction showed that the jpg had less dynamic range and the tonal range was limited as would be expected. There was no difference in White Balance.



Again the top image is the raw image and the lower one the jpg. These images are used for the 'Daylight' images.

I followed the same procedure as outline in the text following the first two images. The only two settings that were different between these two images were Recovery 14/30 and Fill Light 25/15. No local adjustments were deemed to be necessary.

Again the dynamic range is seen in the original enhanced images to be greater in the raw file. White balance there is no difference (the same point in the image chosen in both images for the White Balance tool). The most noticeable difference was in the colours in the sky that are richer in the raw image and have a greater tonal range.



Once more the top image is the raw file and the bottom image the jpg. These images are used for the 'artificial light'. I had assumed that the lighting, top left out of the picture, was tungsten but correction did not fully work.

In this case I kept all settings the same in an attempt to produce the 'same' image. Of course this was doomed to failure because the jpg had already been partly processed in the camera. Comparison showed that the dng image was a more faithful reproduction but that is not surprising because I had tried to recreate the image as I remembered it and of course our eyes quickly adjust to different temperatures of lighting.

General Comments - My Camera's handbook shows that a raw image  creates a 25megapixel file whilst a fine large jpg produces a 6 megapixel file indicating that there is a loss of approximately 75% of the information originally captured.  Presumably there must be a price to pay and whilst this may not be very important in some images it would be in others. Close examination reveals that the loss is found in the gradation of tones across the image where the jpg method combines near colours into an 'average' to allow for compression. Now it can be argued that the human eye may not be able to make the very fine distinctions that compression nullifies but I see this as a poor reason for dumping so much information.

As can be guessed I always shoot in raw as this gives me the best chance of capturing the image before me.







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