Signature's color is incorrect in Android

[dule-vikki]

Hello,

Currently, I am using react-native-pdf@6.7.7 lib in my application
In v6.7.7, lib has installed dependencies like that:

implementation 'com.github.zacharee:AndroidPdfViewer:4.0.1'
implementation 'io.legere:pdfiumandroid:1.0.32'
implementation 'com.google.code.gson:gson:2.13.1'

So far, everything is work find. Only I have an issue with signature color in my pdf file that is the color is blue Instead of red.
Could you help me check this? Thanks.

Expectation (red):

Current (blue):

[johngray1965]

PdfiumAndroidKt provides an android wrapper of Pdfium. We entertain bugs related to the wrapper, and PRs for the wrapper. I don't believe this is either. That's a slightly old version PdfiumAndroidKt (1.0.33 is current). If I had to guess, I'd say the issue in probably the react-native-pdf. We have nothing to do with that project.

[YOEL311]

Hey @johngray1965

After investigating these issues and wonday/react-native-pdf#975, I believe I've identified the root cause of the color transformation problem, where red becomes blue and blue becomes yellowish.

Technical Analysis

The color shifting appears to be caused by incorrect color channel ordering between page and annotation rendering. The observed pattern:

1. Red appearing as Blue: RGB(255,0,0) → BGR(0,0,255)
2. Blue appearing as Yellow-Red: RGB(0,0,255) → BGR(255,0,0)

This consistent swap pattern strongly indicates a byte-order issue where RGB values are being interpreted as BGR or vice versa.

Suspect Code

In commit 22df6de, the rendering code uses:

FPDF_BITMAP pdfBitmap = FPDFBitmap_CreateEx(
    ...,
    FPDFBitmap_BGRA,              // Using BGRA format
    ...
);

int flags = FPDF_REVERSE_BYTE_ORDER;  // With byte order reversal
if(renderAnnot) {
    flags |= FPDF_ANNOT;
}

[johngray1965]

FPDFBitmap_BGRA is the format PDFium wants, and int flags = FPDF_REVERSE_BYTE_ORDER should handle it coming as in opposite direction. What created the PDF? Lots of things are using this don't see this issue.

// More DIB formats
// Unknown or unsupported format.
#define FPDFBitmap_Unknown 0
// Gray scale bitmap, one byte per pixel.
#define FPDFBitmap_Gray 1
// 3 bytes per pixel, byte order: blue, green, red.
#define FPDFBitmap_BGR 2
// 4 bytes per pixel, byte order: blue, green, red, unused.
#define FPDFBitmap_BGRx 3
// 4 bytes per pixel, byte order: blue, green, red, alpha.
#define FPDFBitmap_BGRA 4

That's from a header from pdfium code. That's the order it needs to be sent. If you have a PDF that renders correctly elsewhere, but not with this library, please attach one, then I can look into it. But I don't believe its the code you're referencing. If that was wrong, everything would have the color shifted. Lots of things in PDFs are not what you'd otherwise expect. For instance, coordinate 0,0 is at the bottom left.

[johngray1965]

BTW, it's possible that the problem is either is how you are calling it, how the PDF was constructed or in PDFium. This project is just a wrapper of PDFium, we don't maintain PDFium. If it's in the wrapper, I'll try to fix it. But the footprint in the wrapper is very small.

[YOEL311]

@johngray1965
Thank you for your attention to this issue. I wanted to mention that the color inversion problem specifically occurs with annotations.

[johngray1965]

If you can send a file to test with that has the annotations, I can take a look when I get some free time.

[YOEL311]

Hey @johngray1965,

I tried adding an annotation on a regular PDF, and I couldn’t reproduce the issue.
However, when I use a specific document that contains some personal information, the color inversion does occur.

Thanks again for your help and for looking into this!

@faridyusman, if you’re also experiencing this issue, could you please attach a sample PDF where it happens for you?
Having another example helps narrow down whether the problem is related to specific PDF metadata or structure.