9/20/2023 0 Comments Darktable manualThe mapping process consists of two steps. ![]() The control sample can either be a critical part of your subject that needs to have constant brightness, or a non-moving and consistently-lit surface over your series of images. Spot exposure mapping allows you to define a target brightness, in terms of exposure, for a particular region of the image (the control sample), which you then match against the same target brightness in other images. Each image will still need some individual fine-tuning if you want a perfectly even look over the whole series, and this can be both time-consuming and frustrating. This can be the result of a cloud passing by the sun in natural light, surface reflections having less “shine” from a different angle, or simply due to unavoidable variability in the mechanical diaphragm aperture. Unfortunately, the light often changes slightly between shots, even within the same series captured in the same conditions. In this scenario, you typically develop a single reference image for the whole batch and then copy&paste the development stack to all of the other images in the batch. The spot mapping feature is designed to help with batch-editing a series of images in an efficient way. For example, you can use the relative black exposure slider on the scene tab of the filmic rgb module, or establish a deeper toe in the base curve module. Instead, use a tone mapping curve to add density to the blacks. This can cause problems with some modules later in the pixelpipe. Note: Do not use the black level correction to add more density in blacks as this can clip near-black colors out of gamut by generating negative RGB values. ![]() black level correction (manual and automatic modes) Adjust the black level point to unclip negative RGB values. target level (automatic mode) Define the target level for automatic exposure correction (EV) relative to the white point of the camera. A percentile of 50% denotes a position in the histogram where 50% of pixel values are above and 50% of pixel values are below that exposure. percentile (automatic mode) Define a location in the histogram to use for automatic exposure correction. Use the color picker to sample a portion of the image to be used for this calcuation. clipping threshold (manual mode) Define what percentage of bright values are to be clipped in the calculation of the exposure and black level correction. The color picker tool on the right sets the exposure such that the average of the selected region matches the target lightness defined in spot exposure mapping options. exposure (manual mode) Increase (move to the right) or decrease (move to the left) the exposure value (EV). compensate camera exposure (manual mode) Automatically remove the camera exposure bias (taken from the image’s Exif data). □module controls mode Choose the mode of operation (automatic/manual). A typical use case of automatic mode is deflickering of time-lapse photographs. This mode is particularly useful for automatically altering a large number of images to have the same exposure. Darktable automatically selects the exposure compensation that is required to shift the selected percentile to the selected target level (see definitions below). ![]() This module has two modes of operation: manual Set the exposure, black level and clipping threshold manually automatic (RAW images only) Use an analysis of the image’s histogram to automatically set the exposure. Increase or decrease the overall brightness of an image.
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