SelectPdfImageCodec function

SelectPdfImageCodec is a pure decision helper that compares the EncodedBytes estimates recorded on the candidate and returns which codec should store the image

Each allowed codec is first checked for eligibility: picJpeg requires no alpha, a non-bilevel image, 8 bits per component, 1, 3, or 4 components, and an unknown or greater-than-256 unique color count; picJpx requires a non-bilevel image with at least 8 bits per component and 1 to 4 components; picCcittGroup4 requires a bilevel image without alpha, 1 bit per component, and a single component; picFlate accepts at least 1 bit per component and at least 1 component

Among the eligible codecs the smallest positive EncodedBytes value wins, and the decision reports OriginalBytes, SelectedBytes, and SavedBytes

ReplaceOriginal is True only when the winner is not picKeepOriginal and SavedBytes reaches MinimumSavingBytes; otherwise the decision is reset to picKeepOriginal with zero saved bytes

• MinimumSavingBytes values below 1 are clamped to 1
• A candidate whose original size is zero or negative keeps the original immediately
• No pdfium.dll is needed, so the trade-off can be unit-tested with synthetic candidates