TIFF reader bug when reading 32 bit unsigned monochrome image

[BenBradnick]

I have had success using this library for signed data. However I have a problem with unsigned data. I am using version v3.0.0.0 of the library on Windows 10.

I used the TIFF writer to write a 256x256 image with 32 bits per sample and using the TinyTIFFWriter_UInt format. I set the values of the pixels to x + y*256 where x is the column number and y is the row number.

The written file looks correct and I can check the values with a quick Python script using PIL and numpy (note that PIL uses column-major ordering):

>>> from PIL import Image
>>> import numpy
>>> def check_pixels(array):
...   for y in range(arr.shape[0]):
...     for x in range(arr.shape[1]):
...       expected_value = x + y*arr.shape[1]
...       if expected_value != arr[y,x]:
...         print(f"[{x},{y}] expected: {expected_value}, got: {arr[y][x]}")
...
>>> check_pixels(arr)
>>> image = Image.open(filepath)
>>> arr = numpy.array(image)
>>> check_pixels(arr)
>>> arr.shape
(256, 256)

However when using the TIFF reader I get some peculiar data at specific repeating points in the image.

I read the image using the following code:

    // Open the file using the file reader
    TinyTIFFReaderFile *inputFile = TinyTIFFReader_open(fullFileName.c_str());
    EXPECT_NE(inputFile, nullptr);

    // Check the properties
    EXPECT_EQ(1, TinyTIFFReader_countFrames(inputFile));
    EXPECT_EQ(xSize, TinyTIFFReader_getWidth(inputFile));
    EXPECT_EQ(ySize, TinyTIFFReader_getHeight(inputFile));
    EXPECT_EQ(1, TinyTIFFReader_getSamplesPerPixel(inputFile));
    EXPECT_EQ(32, TinyTIFFReader_getBitsPerSample(inputFile, 0));

    // Read the data and check
    unsigned int *inputData = new unsigned int[xSize*ySize];
    unsigned int counter = 0;
    for (unsigned int y=0; y<ySize; y++)
    {
        for (unsigned int x=0; x<xSize; x++)
        {
            TinyTIFFReader_getSampleData(inputFile, inputData, x + y*xSize);
            if (TinyTIFFReader_wasError(inputFile)) 
            {
                printf("Error reading sample: %s\n", TinyTIFFReader_getLastError(inputFile));
                return;
            } 
            if ((x+y*xSize) != inputData[x+y*xSize])
            {
                printf(
                    "[%d][%d] does not match. Expected: %u, got: %u\n",
                    x, y, x+y*xSize, inputData[x+y*xSize]
                );
                counter++;
                if (counter > 10) return;
            }
            EXPECT_EQ(x+y*xSize, inputData[x+y*xSize]);
        }
    }

    // Close the file
    TinyTIFFReader_close(inputFile);

And I get strange values at these [x][y] coordinates:

[255][63] does not match. Expected: 16383, got: 4107264
[255][127] does not match. Expected: 32767, got: 8301568
[255][191] does not match. Expected: 49151, got: 12495872
[255][255] does not match. Expected: 65535, got: 16690176

I don't see anything obviously wrong with my logic, and it's just 4 values in the entire 256x256 image so I'm wondering if there is a bug in the library itself?