#Fastrawviewer contrast edges how to#
#Fastrawviewer contrast edges code#
#Fastrawviewer contrast edges series#

Standard processing – regular unpacking of RAW data.Since we have already discussed cRAW/ARW2 format, it is easier to understand the other options under Sony ARW2 Data processing: Naturally with such a crude step posterization becomes plainly visible. In our example, after performing decompression through the tone curve the step of 16 becomes 32, that is ≈14-30% of the values characteristic to the background. The delta values during the decompression are multiplied by this step and further decompressed through the curve which you can dump using RawDigger. Dividing 2048 by 128, we have the step of 16. In other words, for a data span of 1178 the nearest larger number that is an exact power of 2 is 2048 = 2 11.

#Fastrawviewer contrast edges code#

In order to code values up to 1178 in 7 bits we need to set the step to 16: 2 ceiling(log 2 (1178/128)) = 16. The minimum value is 296 (compression applied to 80)ĭata span = (max – min) = (1474 – 296) = 1178.The maximum value is 1474 (compression applied to 4080).The sky around the trail is a smooth featureless background, and the pixel values close to the trail range from 80 to 200.Īpplying compression tone curve to this data:.The star trail proper has pixel values that reach as high as 4080.Inspecting the green channel, we can see that the RAW values in the proximity of the track (black level is subtracted) are: During the raw conversion, first, the delta encoding is reversed, next, the linearization tone curve (contained in the metadata of Sony ARW2 files) is applied to decompress the data, and finally the black level (also taken from metadata) is subtracted from the result.Īfter black level subtraction Sony cRAW linearization tone curve is effectively this:.In other words, if the chunk of 32 pixels spans across an area that contains a large variation in brightness, the data in the block is not exact, but is only an approximation.

For a larger span, the scheme does introduce the rounding error, which may lead to posterization. For a data span of less than or equal to 128, the factor is 1, and no rounding error is introduced while reversing the delta encoding. The larger the data span in a 16-pixel block is, the larger the step is, which is multiplied by the delta value to restore the pixel value, and consequently the larger the data step is. Thus the raw data compressed per cRAW scheme effectively uses 1 byte per pixel but the total ARW2 file size is slightly larger as it contains not only cRAW data, but also metadata and JPEG preview. Here, Max is the maximum pixel value in the block, Min is the minimum value in the block, Offsets are the positions of pixels with Max and Min values relative to the block startĭelta = (PixelValue – Min) / Step (see more on this below) The artifacts in the form of a horizontal color fringe on both sides of one of the star trails are very visible even if all of the sliders are set to zero, except the exposure slider: Koski who now gave us his permission to link to the original raw file _DSC0035-startrails.ARW Lets have a look at the example provided by Matti Koski, it is the same example that was published by Lloyd Chambers in his blog. All that is necessary for the artifacts to threaten the quality of the final image is a combination of high local contrast and a flat featureless background. With some unlucky stars in alignment, the artifacts can become plainly visible, even without much image processing. In the vast majority of cases, the compression artifacts are imperceptible unless the heavy-handed contrast boost is introduced. We will be discussing the technical details of this compression in the second part of this article.

#Fastrawviewer contrast edges how to#

The first part of this article is showing how to detect artifacts caused by this compression.

#Fastrawviewer contrast edges series#

Lossy compression of raw data is currently the only option available in Sony cameras of series NEX, SLT, RX, ILCE, ILCA, and the recent DSLR-A.