Why a GIMP Photo Blend Changes Between Linear and Perceptual Spaces
By ImgHeal · Updated
A repair's appearance can change even when its image layers and opacity values stay the same. GIMP offers choices about the space used in processing and compositing. Treat these as part of the document's editing setup, not as proof that the source photograph changed exposure.
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Record the current document setup
Keep a retained project copy and note the layer mode, opacity, image encoding, and any relevant blend-space controls available in your GIMP version. Select one smooth transition and one textured area for comparison. Do not change a color profile at the same time; profile interpretation and compositing calculations are different questions. A darker preview after changing a processing option does not automatically mean that the embedded profile is wrong or that the image needs a compensating brightness adjustment.
Make one controlled comparison
On the duplicate, change only the relevant documented compositing or encoding choice and compare the same regions. Linear-light and perceptually encoded calculations can combine values differently, particularly through soft transitions and blend modes. Inspect the complete stack, because a local patch may depend on several layers rather than one. Keep the option that supports the intended documented workflow, not simply the brightest preview. Avoid converting repeatedly between low-precision representations while experimenting; retain enough source information to revisit the decision.
Check the approved composite normally
After choosing the setup, reassess any tonal adjustments previously added to compensate for the other appearance. Compare the photograph with its untouched scan at matching scale and reopen a separate viewing export. Keep project settings in the edit record so another editor can understand the choice. The effect of a processing space is not an authenticity test for old paper tone or skin color. If the original color evidence is uncertain, describe that uncertainty even when one compositing option makes the image appear more natural.
Check the working document
- Profile interpretation and compositing were separated.
- Only one processing choice changed during the test.
- Compensating tonal edits were reassessed.
Sources and further reading
- GIMP: Image encodingDocuments processing precision, channel encoding, and conversion dithering.
Questions about this restoration task
Is Linear light always the most accurate-looking option?
No single visual preference establishes historical accuracy. Use the documented workflow and sufficient precision, then compare the resulting image with reliable source evidence.
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